High molecular weight hyaluronic acid increases the differentiation potential of the murine chondrocytic ATDC5 cell line

Osteoarthritis (OA) is a group of common, chronic, and painful inflammatory joint diseases. One important finding in OA patients is a remarkable decrease in the molecular weight of hyaluronic acid (HA) in the synovial fluid of affected joints. Therapeutic HA is available to patients in most parts of the world as a viscosupplementation product for the treatment of OA. Previous clinical reports show that high molecular weight HA (HMWHA) more effectively relieves pain than low molecular weight HA (LMWHA). However, the mechanism behind this finding remains unclear. In this study, we investigated whether a LMWHA (Low‐0.9 MDa) and two types of HMWHA (High‐1.9 MDa and 6 MDa) differentially affected chondroregulatory action. We tested this using ATDC5 cell, a murine chondrocytic cell line widely used in culture systems to study chondrogenic differentiation. We found that HMWHA, especially hylan G‐F 20 (High‐6 MDa), significantly induced aggrecan and proteoglycan accumulation, nodule formation, and mRNA expression of chondrogenic differentiation markers in a time‐ and dose‐dependent manner. In addition, we showed that HMWHA prevented TNF‐α induced inhibition of chondrogenic differentiation, with no effect on cell proliferation or viability. These results reveal that HMWHA significantly promotes chondrogenic differentiation of ATDC5 cells in vitro, and suggest that HMWHA plays a significant chondroregulatory role in vivo. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:1619–1627, 2014.     

Crystallization and preliminary X‐ray diffraction analysis of eukaryotic α2‐macroglobulin family members modified by methylamine,proteases and glycosidases

α₂‐Macroglobulin (α₂M) has many functions in vertebrate physiology. To understand the basis of such functions, high‐resolution structural models of its conformations and complexes with interacting partners are required. In an attempt to grow crystals that diffract to high or medium resolution, we isolated native human α₂M (hα₂M) and its counterpart from chicken egg white (ovostatin) from natural sources. We developed specific purification protocols, and modified the purified proteins either by deglycosylation or by conversion to their induced forms. Native proteins yielded macroscopically disordered crystals or crystals only diffracting to very low resolution (>20 Å), respectively. Optimization of native hα₂M crystals by varying chemical conditions was unsuccessful, while dehydration of native ovostatin crystals improved diffraction only slightly (10 Å). Moreover, treatment with several glycosidases hindered crystallization. Both proteins formed spherulites that were unsuitable for X‐ray analysis, owing to a reduction of protein stability or an increase in sample heterogeneity. In contrast, transforming the native proteins to their induced forms by reaction either with methylamine or with peptidases (thermolysin and chymotrypsin) rendered well‐shaped crystals routinely diffracting below 7 Å in a reproducible manner.     

Ultra-high-resolution paleoenvironmental records via direct laser-based analysis of lipid biomarkers in sediment core samples

Marine microorganisms adapt to their habitat by structural modification of their membrane lipids. This concept is the basis of numerous molecular proxies used for paleoenvironmental reconstruction. Archaeal tetraether lipids from ubiquitous marine planktonic archaea are particularly abundant, well preserved in the sedimentary record and used in several molecular proxies. We here introduce the direct, extraction-free analysis of these compounds in intact sediment core sections using laser desorption ionization (LDI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). LDI FTICR-MS can detect the target lipids in single submillimeter-sized spots on sediment sections, equivalent to a sample mass in the nanogram range, and could thus pave the way for biomarker-based reconstruction of past environments and ecosystems at subannual to decadal resolution. We demonstrate that ratios of selected archaeal tetraethers acquired by LDI FTICR-MS are highly correlated with values obtained by conventional liquid chromatography/MS protocols. The ratio of the major archaeal lipids, caldarchaeol and crenarchaeol, analyzed in a 6.2-cm intact section of Mediterranean sapropel S1 at 250-µm resolution (∼4-y temporal resolution), provides an unprecedented view of the fine-scale patchiness of sedimentary biomarker distributions and the processes involved in proxy signal formation. Temporal variations of this lipid ratio indicate a strong influence of the ∼200-y de Vries solar cycle on reconstructed sea surface temperatures with possible amplitudes of several degrees, and suggest signal amplification by a complex interplay of ecological and environmental factors. Laser-based biomarker analysis of geological samples has the potential to revolutionize molecular stratigraphic studies of paleoenvironments.Microbial lipids in aquatic sediments reflect phylogeny, environmental conditions, and biogeochemistry of the water column in which they were produced. After sedimentation and because of the persistence of lipid structures in the sedimentary record, the information archived in these lipids remains available on geological time scales. Retrieval of this information from sediments and rocks has increasingly contributed to our understanding of past environments, microbial communities, and biogeochemical processes (e.g., refs. 1–5). Merged with the concept of molecular stratigraphy (2, 6), i.e., the analysis of selected biomarkers in solvent extracts of sediment samples in a stratigraphic framework, unique information can be gleaned regarding the temporal changes of past ecological and environmental conditions in aquatic systems. Because of analytical requirements, the temporal resolution is typically limited by centimeter-scale-sized samples, which, dependent on the depositional setting, tend to integrate time periods of decades to millennia, even in high-sedimentation settings such as the Santa Barbara Basin (e.g., refs. 4, 7, 8). In consequence, our knowledge of the temporal changes of the environmental and ecological history recorded by lipid biomarkers is rather coarse and based on long-term averages of their distributions in the sedimentary record.In this study we seek to extend this approach to ultra-high-resolution molecular stratigraphy. We focused on archaeal glycerol dialkyl glycerol tetraethers (GDGTs), which are produced by planktonic archaeal communities and are ubiquitous and persistent components in marine sediments (e.g., refs. 9, 10) with widely recognized potential for paleoenvironmental studies. The number of cycloalkyl rings in GDGTs (Fig. S1) appears highly sensitive to ecological and environmental factors such as phylogeny (ref. 5 and references therein), temperature (ref. 11 and references therein), or pH (12, 13). This sensitivity of GDGT composition to environmental and ecological factors has driven the development of multiple molecular proxies. Adaptation to temperature has been demonstrated in thermophilic cultures of archaea (e.g., ref. 14) and serves as concept for the reconstruction of paleo sea surface temperatures (SST) in sediments using the TEX₈₆ (tetraether index of 86 carbon atoms) (3), which is based on fossil lipids of planktonic archaea. This proxy has been used to characterize oscillations of SST in different geological episodes (e.g., refs. 8, 15, 16). Complications could arise from additional GDGT sources, e.g., allochthonous inputs of GDGT-bearing soils, lateral transport, in situ production, and/or recycling by sedimentary archaea (cf. refs. 5, 17). Relative GDGT distributions required for proxy calculations are obtained by HPLC atmospheric pressure chemical ionization mass spectrometry (HPLC/APCI-MS) of solvent extracts from gram-sized sediment samples (18, 19).To enhance temporal resolution of GDGT-based proxies, we explored the utility of laser desorption ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry (LDI FTICR-MS). In LDI, the impact of a pulsed laser beam on the sample leads to desorption, vaporization and ionization of the analytes, forming a cloud of charged molecules. An additional matrix is frequently applied to facilitate the generation of ions (matrix assisted laser desorption ionization [MALDI]). A complete understanding of underlying ionization mechanisms has not been achieved yet (20). LDI or MALDI are best known in the field of proteins or peptides and have also been successfully used in lipid research (21). The fact that LDI analysis can generate ions directly from the sample placed on a sample holder without time-consuming wet-chemical pretreatment while producing mass spectra from submillimeter-sized spots (as small as 10 µm) makes this technique particularly attractive for molecular stratigraphy. LDI may allow direct analysis of nanogram-sized samples on the surface of cut, intact sediment cores at ultra-high spatial resolution, equivalent to temporal resolution on the order of months to decades.We aimed to develop a technique that takes advantage of both the exquisite sensitivity and unequivocal molecular information of ultra-high-resolution mass spectrometry by FTICR-MS and the high spatial resolution of LDI within an intact and unaltered sedimentological context. The key steps of validation and implementation included (Fig. S2) (i) the detection of archaeal GDGTs, (ii) verification of results obtained by LDI FTICR-MS by parallel analysis using established HPLC/APCI-MS methods, and (iii) the examination of the first continuous high-resolution GDGT profile from a sediment core section of the eastern Mediterranean sapropel S1, which was deposited under anoxic conditions during the Holocene climatic optimum (HCO; refs. 22, 23). The data thus may provide an unprecedented view of the dynamic variations of both SST and ecological and environmental factors during sapropel formation.     

Acoustic excitations and elastic heterogeneities in disordered solids

In the recent years, much attention has been devoted to the inhomogeneous nature of the mechanical response at the nanoscale in disordered solids. Clearly, the elastic heterogeneities that have been characterized in this context are expected to strongly affect the nature of the sound waves which, in contrast to the case of perfect crystals, cannot be completely rationalized in terms of phonons. Building on previous work on a toy model showing an amorphization transition, we investigate the relationship between sound waves and elastic heterogeneities in a unified framework by continuously interpolating from the perfect crystal, through increasingly defective phases, to fully developed glasses. We provide strong evidence of a direct correlation between sound wave features and the extent of the heterogeneous mechanical response at the nanoscale.In crystals, molecules thermally oscillate around the periodic lattice sites and vibrational excitations are well understood in terms of quantized plane waves, the phonons (1). The vibrational density of states (vDOS) in the low-frequency regime is well described by the Debye model, where the vibrational modes are the acoustic phonons. In contrast, disordered solids, including structural glasses and disordered crystals, exhibit specific vibrational properties compared with the corresponding pure crystalline phases. It is not possible here to give a fair review of the extensive theoretical and experimental work generated by these issues; we therefore mention below a few facts that we consider the most relevant in the present context. The origin of the vDOS modes in excess over the Debye prediction around ω ∼1 THz, the so-called Boson peak (BP), is still debated (see, among many others, refs. 2 and 3). At the BP frequency, Ω^BP, localized modes have also been observed (4). Acoustic plane waves, which are exact normal modes in crystals, can still propagate in disordered solids. Indeed, at low frequencies, Ω, and long wavelengths, Λ, acoustic sound waves do not interact with disorder and can propagate conforming to the expected macroscopic limit. However, as Ω is increased beyond the Ioffe–Regel (IR) limit, Ω^IR, acoustic excitations interact with the disorder and are significantly scattered (5–7). Interestingly, this strong scattering regime occurs around the BP position, Ω^IR ∼ Ω^BP (8, 9). The exact origin of this phenomenon and its connection to the BP remain elusive.A possible rationalization of the above issues is based on the existence of elastic heterogeneities (10), which can originate from structural disorder, as in structural glasses (2), or disordered interparticle potentials, even in lattice structures such as disordered colloidal crystals (11). In the heterogeneous-elasticity theory of refs. 7 and 12 this amounts to consider spatial statistical fluctuations of the shear modulus. Within the framework of jamming approaches and using effective medium theories, elastic heterogeneities are related to the proximity of local elastic instabilities (13). Recent simulation work (14–16) has clearly demonstrated their existence in disordered solids. This is at variance with the case of simple crystals, which are characterized by a fully affine response and homogeneous moduli distributions (17). More specifically, in the large length scale limit, macroscopic moduli are observed. In contrast, as the length scale is reduced, moduli heterogeneities are detected, at a typical length scale ξ ≃ 10−15σ (15), where σ is the typical atomic diameter. Breakdown of both continuum mechanics (18) and Debye approximation (5, 6) has been demonstrated at the same mesoscopic length-scale ξ, where they are still valid for crystals. Remarkably, the wave frequency corresponding to the wavelength Λ ∼ ξ is very close to Ω^IR ∼ Ω^BP (19). Altogether these results indicate that a close connection must exist between elastic heterogeneities and acoustic excitations. In this paper we precisely address this point.In ref. 20 we considered a numerical model featuring an amorphization transition (21). We showed how to systematically deform the local moduli distributions, evaluated by coarse-graining the system in small domains of linear length scale w. We characterized the degree of elastic heterogeneity in terms of SD of those distributions and studied the effect on normal modes (eigenvalues of the Hessian matrix) and thermal conductivity. Building on that work, we are now in the position to investigate the relation between elastic heterogeneities and acoustic excitations, unifying in a single framework ordered and disordered solid states and considering quantities directly probed by experiments. By interpolating in a controlled way from perfect crystals, through increasingly defective phases, to fully developed amorphous structures, we (i) calculate the dynamical structure factors, extracting the relevant spectroscopic parameters; (ii) characterize the wave vector dependence of sound velocity and broadening of the acoustic excitations and clarify their nature in terms of the IR limit; and (iii) provide, for the first time to our knowledge, direct evidence of the correlation of the excitations lifetimes and Ω^IR with the magnitude of the elastic heterogeneities.     

Effects of differential habitat warming on complex communities

Food webs unfold across a mosaic of micro and macro habitats, with each habitat coupled by mobile consumers that behave in response to local environmental conditions. Despite this fundamental characteristic of nature, research on how climate change will affect whole ecosystems has overlooked (i) that climate warming will generally affect habitats differently and (ii) that mobile consumers may respond to this differential change in a manner that may fundamentally alter the energy pathways that sustain ecosystems. This reasoning suggests a powerful, but largely unexplored, avenue for studying the impacts of climate change on ecosystem functioning. Here, we use lake ecosystems to show that predictable behavioral adjustments to local temperature differentials govern a fundamental structural shift across 54 food webs. Data show that the trophic pathways from basal resources to a cold-adapted predator shift toward greater reliance on a cold-water refuge habitat, and food chain length increases, as air temperatures rise. Notably, cold-adapted predator behavior may substantially drive this decoupling effect across the climatic range in our study independent of warmer-adapted species responses (for example, changes in near-shore species abundance and predator absence). Such modifications reflect a flexible food web architecture that requires more attention from climate change research. The trophic pathway restructuring documented here is expected to alter biomass accumulation, through the regulation of energy fluxes to predators, and thus potentially threatens ecosystem sustainability in times of rapid environmental change.Natural systems are inherently complex entities, wherein organisms act as agents of material and biomass transport (1) weaving food webs through a mosaic thermal environment. Direct temperature effects on trophic interactions arise through thermal regulation of an organism’s physiology and behavior (2–5). For ecotherms (that is, organisms whose body temperature is aligned with ambient temperature), several biological rates show unimodal responses to temperature (2, 3, 6), and correspondingly, studies have shown that consumption rates initially rise with warming to a peak rate and then fall rapidly approaching a critical temperature (6). Understanding the ways that these organism responses alter food webs, and how these food web responses affect ecosystem function, are key requirements to predicting climate change impacts on ecosystems (7–11).A simple way to think about temperature’s effects on any single trophic interaction is through the general linear consumption function:Consumption(per?capita) = a?t_s?R, [1]where a is the attack rate, t_s is the time searching, and R is the resource biomass density. The direct effects of temperature on an organism’s ability to encounter and capture resources in a given habitat may largely depend on a, and t_s (with potential indirect effects relative to the consumer through temperature influences on R). The argument for the temperature dependence of attack rate (a) is relatively straightforward. Temperature mediates foraging velocity (3), and considering all else equal, velocity determines encounter rates and prey capture success. The influence of temperature on time searching is a little more complex, but the general expectation is that its influence will be shaped by the requirement that the organism allocate its feeding time in different patches or habitats to increase its fitness (5). Such thermal limitation of search time would lead to reductions of interaction strength in warming habitats—in effect, temperature would mediate prey availability (e.g., when temperature exceeds physiological limits). What remains to complete the consumption equation above is the effect of temperature on R, both the direct effects (for example, the impact of warming on R’s productivity) and indirect effects (for example, impact of warming on the number and consumption capabilities of consumers competing for R) (12, 13). Note that the numerical response (i.e., biomass accumulation) of the consumer may depend on additional vital rates (e.g., conversion efficiency). The conversion of prey biomass to predator biomass (often denoted e) may not change with temperature (2, 3), although recent research suggests that e may be temperature dependent if consumers switch among resources with different elemental composition to balance changing metabolic and somatic demands (14). Nevertheless, we focus on consumption (a, t_s, R) as a means to build an argument for temperature’s influence on trophic structure.Here, we extend the logic that underlies this simple representation of temperature-dependent consumption to develop hypotheses that link temperature differentials, through direct and indirect means, to spatial food web structure. Spatially simple laboratory studies of food webs suggest that larger-bodied, higher trophic level organisms are likely to have high extinction risk with ambient warming (15). In natural systems, these higher-order predators provide a spatially unifying component to food webs: their high mobility enables them to forage among different habitats, coupling food chains with unique basal resource groups (16–18). This coupling structure can be an important part of sustaining higher-order consumers with consequences for food chain length, trophic control, and ecosystem stability (16, 19–21). For example, theory argues that reduced access to a novel resource compartment may decrease a consumer’s biomass (19, 20), thereby increasing the chance of local extinction from a random event. When accessibility is limited, reduced coupling may alter food chain length if habitats contain prey that differ in trophic position (22) or if higher level prey increase, with reduced trophic control, and consequently predators become less omnivorous (19, 21). Given that temperature change can drive asymmetric responses in species that differ in thermal tolerance, the influence of spatially structuring elements on the response of a food web to warming will depend not only on the direct responses of consumers to temperature (2, 3, 5) but also those responses of other interacting community members (i.e., resources and competing predators) (12, 13, 23). We test notions of the structuring effects of differential temperature on spatially coupled food webs (thermal-accessibility hypothesis), using boreal lakes as a natural study system (Fig. 1). To make this test, we assembled one of the largest comparative food web datasets on record: 54 ecosystems, characterized using >3,000 isotope (N and C) samples.Open in a separate windowFig. 1.Simple schematic showing expected effects of differential warming on habitat coupling (horizontal axis) and habitat use (vertical axis) by lake trout in cold (Upper) and warm (Lower) lakes. A thermal accessibility argument predicts that lake trout couple into the thermally exposed near-shore resource channel less and should use (proportionally) that habitat less under warmer conditions (indicated by lake trout position). The arrow direction and thickness indicate coupling direction and strength. The letters in the upper diagram identify trophic groups used in both cold (Upper) and warm (Lower) lake depictions: lake trout (a), pelagic forage fish (b), pelagic invertebrates (c), pelagic phytoplankton (d), littoral fish (e), littoral invertebrates (f), and benthic algae (g). To the right in the diagram, we show thermal profile data contrasting temperature at depth from Victoria Lake [cold; summer air temperature, 15.5 °C; latitude (lat), 49.62306; longitude (long), −91.54889] and Charleston Lake (warm; summer air temperature, 19.7 °C; lat, 44.53611; long, −76.01194) taken at the time of sampling. Temperature is visually highlighted with darker blue (cold) and darker red (warm) hues. These lakes experience temperatures near the cold and warm endpoints for our dataset and are of the same order of magnitude in size, and both had thermal profiles recorded to 30 m.Freshwater lakes are particularly sensitive to climate change as lake habitats are structured by climate-driven water temperature and many biota are vulnerable to ambient temperature change (24). A key habitat feature of boreal lakes is thermal stratification, an effect of antagonistic physical forces of mixing by wind energy and resistance to mixing by solar heating that separates cold, more dense water (hypolimnion) from warmer, less dense surface water (epilimnion) (25). The stratification process creates a potential for temperature differentials between deeper offshore and shallower near-shore subhabitats within a lake, as temperatures remain relatively constant in deep habitats, whereas shallower near-shore temperatures are strongly influenced by air temperatures (26). Monitoring in the boreal region (27, 28) has shown that rising air temperature warms surface waters, accelerates the stratification process, and extends the duration of stratification; thus, air temperature is a primary determinant of lake thermal heterogeneity.Most aquatic organisms (e.g., invertebrates, amphibians, fish) are ectotherms; therefore, the demands of the thermal environment arguably form the most influential set of abiotic factors aquatic organisms must satisfy (29, 30) (including increased oxygen requirements in warmer water). Thermal differentiation in lakes typically corresponds with the species differences that characterize offshore and near-shore habitats. Conveniently, biomass flow from these habitats through a food web can be traced using stable carbon and nitrogen isotope ratios due to isotope differences at the base of the food web between phytoplankton (offshore) and benthic algae (near-shore) (18, 22, 31, 32).We focus our study on the trophic pathways that flow from basal resources to lake trout (Salvelinus namaycush), a vulnerable, cold-adapted (10–12 °C preference) apex predator (33) estimated to reside in 66,500 Canadian lakes (34) (Fig. 1). Previous studies show that lake trout play a keystone structural role in integrating resource pools in offshore and near-shore habitats (18, 21, 22, 31). In what follows, we test the direct and indirect effects of differential warming on this natural system (lake trout food web) across a summer mean temperature gradient ranging 15–20 °C. At the warmer end of this range, surface water temperatures will often exceed the physiological tolerance of lake trout and should restrict accessibility into the near-shore habitat (Fig. 1, Lower). Given this thermal mechanism, we predict that lake trout in warmer climates may change their habitat use to deeper waters and this spatial behavior may shift the degree that near-shore resource pools are coupled by this predator relative to cooler climates (Fig. 1). We further consider whether spatial responses are associated with a shift in the length of the apex predator’s food chain. This thermal-accessibility–mediated restructuring of fundamental food web structure is considered along with complementary notions of warm-tolerant competitor effects and relative prey abundance changes with climate.     

Autism spectrum disorder severity reflects the average contribution of de novo and familial influences

Autism spectrum disorders (ASDs) are a highly heterogeneous group of conditions—phenotypically and genetically—although the link between phenotypic variation and differences in genetic architecture is unclear. This study aimed to determine whether differences in cognitive impairment and symptom severity reflect variation in the degree to which ASD cases reflect de novo or familial influences. Using data from more than 2,000 simplex cases of ASD, we examined the relationship between intelligence quotient (IQ), behavior and language assessments, and rate of de novo loss of function (LOF) mutations and family history of broadly defined psychiatric disease (depressive disorders, bipolar disorder, and schizophrenia; history of psychiatric hospitalization). Proband IQ was negatively associated with de novo LOF rate (P = 0.03) and positively associated with family history of psychiatric disease (P = 0.003). Female cases had a higher frequency of sporadic genetic events across the severity distribution (P = 0.01). High rates of LOF mutation and low frequencies of family history of psychiatric illness were seen in individuals who were unable to complete a traditional IQ test, a group with the greatest degree of language and behavioral impairment. These analyses provide strong evidence that familial risk for neuropsychiatric disease becomes more relevant to ASD etiology as cases become higher functioning. The findings of this study reinforce that there are many routes to the diagnostic category of autism and could lead to genetic studies with more specific insights into individual cases.The set of conditions diagnosed as autism spectrum disorders (ASDs) vary enormously in their presentation (1). The most severely impaired individuals—often those with intellectual disabilities, limited speech, and severe behavioral problems—can require lifelong care. At the other end of the functional spectrum, people diagnosed with ASDs can be verbally fluent and academically gifted and can achieve independence in adulthood (2, 3). The broad range of cognitive and behavioral profiles seen in diagnosed ASDs has been long viewed as a challenge by the research community (4). Although it is well established that (i) the cognitive/behavioral profile of people diagnosed with ASDs varies widely and (ii) the set of genetic factors related to ASDs varies widely (5, 6), the degree to which phenotype can be used to predict patterns in disease architecture remains unclear.Recent insights into the genetic influences on ASDs offer an opportunity to investigate this question through the lens of de novo vs. familial effects. On average, ASDs run in families. The siblings of children with ASDs are 10–20 times more likely to receive a diagnosis of ASD themselves (7, 8); the parents of children with ASDs are more likely to manifest autistic features, as well as a variety of other neuropsychiatric conditions, such as schizophrenia and bipolar disorder (9, 10). These epidemiologic observations are consistent with analyses suggesting that ASDs are influenced by thousands of common genetic variants transmitted between generations. It has been estimated that common, genotyped SNPs account for 20–60% of variation in ASD risk, although the effect of any individual SNP is likely very small (11–13). Many of these influences are shared with other psychiatric disorders (12, 14), which at least in part explains the familial clustering of different types of behavior problems.However, statistics about ASD heritability reflect an average. For example, there are likely many affected families for whom sibling recurrence risk is less than 10–20%. The strongest evidence toward this claim comes from studies of rare, severely deleterious genetic events that are associated with ASDs (15–20). Events of this type, for example copy number variants and loss of function (LOF) mutations, are often de novo (not seen in an affected individual’s parents). Although cases of ASDs involving a de novo mutation could reflect a concert of spontaneous and inherited genetic events, de novo events of large effect may reduce the likelihood of seeing psychiatric problems in an affected individual’s family members.     

Charge transport and rectification in molecular junctions formed with carbon-based electrodes

Molecular junctions formed using the scanning-tunneling-microscope–based break-junction technique (STM-BJ) have provided unique insight into charge transport at the nanoscale. In most prior work, the same metal, typically Au, Pt, or Ag, is used for both tip and substrate. For such noble metal electrodes, the density of electronic states is approximately constant within a narrow energy window relevant to charge transport. Here, we form molecular junctions using the STM-BJ technique, with an Au metal tip and a microfabricated graphite substrate, and measure the conductance of a series of graphite/amine-terminated oligophenyl/Au molecular junctions. The remarkable mechanical strength of graphite and the single-crystal properties of our substrates allow measurements over few thousand junctions without any change in the surface properties. We show that conductance decays exponentially with molecular backbone length with a decay constant that is essentially the same as that for measurements with two Au electrodes. More importantly, despite the inherent symmetry of the oligophenylamines, we observe rectification in these junctions. State-of-art ab initio conductance calculations are in good agreement with experiment, and explain the rectification. We show that the highly energy-dependent graphite density of states contributes variations in transmission that, when coupled with an asymmetric voltage drop across the junction, leads to the observed rectification. Together, our measurements and calculations show how functionality may emerge from hybrid molecular-scale devices purposefully designed with different electrodes beyond the so-called “wide band limit,” opening up the possibility of assembling molecular junctions with dissimilar electrodes using layered 2D materials.Recent interest in understanding charge transport in molecular-scale devices and at metal/organic interfaces has led to innovations in both experimental and theoretical techniques designed to probe such devices (1, 2). Molecular junctions in a metal–molecule–metal motif using a variety of metals including Au, Ag, Pt, Al, and Cu have been studied extensively (3–7), contributing significantly to our understanding of the fundamental principles required to realize molecular-scale electronic components such as rectifiers or switches (8–14). However, the nanogap electrodes using such metals are mechanically unstable due to the high atomic mobility of metal atoms (15–18) and all except for Au oxidize easily under ambient conditions (6). Furthermore, the electrode density of states near the Fermi energy is typically nearly energy independent. This results in molecular junctions formed with metals having rather smooth and featureless transmission probabilities around the Fermi energy, limiting their applications. Carbon-based electrodes such as graphite have remarkable mechanical strength as well as a nonconstant highly dispersive density of states near its Fermi energy (19). In addition, molecules can be bonded covalently to carbon-based materials and can also bind through a van der Waals-based π–π stacking interaction (20). However, to date, such materials have not been used to create molecular junctions using the scanning-tunneling-microscope–based break-junction technique (STM-BJ). All-carbon electrodes have been used in the past, including carbon nanotubes and graphene (21–23); however, such devices are not easy to fabricate and characterize electronically with a statistically significant method. Moreover, there have been no computational studies on such junctions aimed at understanding the relation between charge transport and electrode properties.Here, we measure the conductance of a series of graphite/amine-terminated oligophenyl/Au molecular junctions using the STM-BJ technique (4). We show that the conductance of this series decays exponentially with molecular backbone length with a decay constant that is essentially the same as that for measurements with Au electrodes. We show further that these molecular junctions rectify (14, 24), due to an asymmetry in the coupling of the molecule with the Au and graphite electrodes. The nature and magnitude of the rectification is directly connected to the nonconstant density of states of graphite near the Fermi level. The trends from self-energy–corrected density functional theory calculations are in agreement with our experimental results; specifically, we find that junction conductance decreases as the junction is elongated, as the angle between the molecule and the graphite substrate increases. These measurements and calculations together demonstrate new classes of molecular junctions with dissimilar electrodes using layered 2D electrodes.     

Diagnosing skin rejection in vascularized composite allotransplantation: advances and challenges

Refinements in microsurgical techniques coupled with advances in immunosuppressive and immunomodulatory protocols have enabled broader clinical application of vascularized composite allotransplantation (VCA) with encouraging immunological, functional, and esthetic results. However, skin rejection remains a significant obstacle and a serious complication for VCA recipients. Clinical and histopathological features of rejection in VCA have been described in a number of studies, which led to the development of an international consensus on the classification guidelines of rejection in the context of VCA. Nevertheless, currently available diagnostic modalities still have several limitations and shortcomings that can pose a significant diagnostic challenge, particularly when signs of rejection are found to be equivocal. In this review, we provide a critical analysis of these advances and challenges in diagnosing skin rejection. Specifically, we highlight the gaps in understanding of rejection mechanisms, the shortfalls in correlating cellular, molecular, and clinicopathologic markers with rejection grades, deficiencies in defining chronic rejection, and antibody‐mediated rejection after VCA, as well as providing an outlook on novel concepts, such as the utilization of advanced computational analyses and cross‐disciplinary diagnostic approaches.     

低分子肝素治疗糖尿病肾病的疗效观察

目的 :探讨低分子肝素 (LMWH)治疗糖尿病肾病的疗效。方法 :随机将 2 3例糖尿病肾病患者分为二组 ,对照组 12例 ,给予降糖以及洛丁新和肠溶阿斯匹林口服治疗。观察组 11例则在此基础上加用低分子肝素。结果 :治疗 6周后观测二组尿蛋白、血浆蛋白、肌酐清除率、血脂、纤维蛋白原及浮肿程度均较治疗前改善 ,而治疗组明显优于对照组 (P <0 .0 1及P <0 .0 5 ) ,凝血指标无明显差异。结论 :LMWH可明显改善糖尿病肾病的蛋白尿和浮肿 ,而无明显出血等副作用。     

硫氧还蛋白基因TXN单核苷酸多态性与中国汉族人群肺癌易感性研究

目的 探讨硫氧还蛋白基因TXN的单核苷酸多态性与肺癌易感性间的关系.方法 采集经病理组织学确诊的肺癌患者292例,相同地区、性别、年龄频数匹配的体检健康对照307例,针对筛选出的TXN基因9个单核苷酸多态性(SNP)位点进行基因型检测,通过统计分析研究基因频率与肺癌风险的关系,并探讨吸烟在其中的影响.结果 3个TXN基...