Impact of age and body size on inter-individual variation in measures of lipid metabolism: influence of gender and apolipoprotein E genotype

This study was undertaken in 1695 adult subjects (870 women and 825 men) in order to further document the complexity of the influence of the apolipoprotein (apo) E genotypes on the mean levels and intragenotypic variability of seven measures of lipid metabolism. In addition, the statistical relationships between variability in these traits and variation in age, body mass index (BMI) and waist-to-hip ratio (WHR) were assessed. The contribution of variation in age and body size to inter-individual variation was found to be dependent on context, defined by gender and apo E genotype. Our findings are consistent with the reality that it is neither genes nor environments, but their interactions that are responsible for the variation in risk of cardiovascular disease.     

Exploring Variations in Individuals’ Relationships to Sexual Fantasies: A Latent Class Analysis

Sexual fantasies represent a vast and highly personal dimension of human sexuality that remains understudied empirically. This article used a person-oriented approach to examine the reactions of arousal and discomfort that individuals experienced in response to four proposed fantasy scenarios depicting themes of romance, power dynamics (i.e., submission and domination), pain (i.e., sadism and masochism), and sexual violence. Using an online sample of 566 adult participants (250 men and 291 women) from the general population of Canada and the U.S., four classes were identified based on reactions of arousal and discomfort toward the proposed scenarios: Indifferent (relatively low arousal and discomfort to all scenarios, 37%), Romantic (high arousal solely for the romance scenario, high discomfort toward other scenarios, 22%), Enthusiastic (high arousal and low discomfort in response to all scenarios, 26%), and Dissonant (relatively high arousal and discomfort toward all scenarios, 15%). These classes were then compared to examine differences in terms of the following psychosexual characteristics: gender, experiences of childhood sexual abuse, sexual compulsion, and romantic attachment. Findings illustrated distinct patterns of reactions toward fantasies and confirmed the presence of links between reactions toward sexual fantasies, psychosexual characteristics, and traumatic life experiences. This suggests that the relationship between individuals and their sexual fantasies may be indicative of their overall relationship with sexuality.

     

Treatment of palmoplantar psoriasis with infliximab: a randomized,double‐blind placebo‐controlled study

Background Palmoplantar psoriasis is a difficult to treat variant of plaque psoriasis. Objective To study the safety and efficacy of infliximab in non‐pustular palmoplantar psoriasis. Methods Patients with non‐pustular palmoplantar psoriasis affecting at least 10% of their palms and soles and with a modified palmoplantar psoriasis area and severity index (m‐PPPASI) of at least eight were recruited. Patients were randomized (1:1) to receive infliximab 5 mg/kg or placebo at weeks 0, 2 and 6. Patients initially randomized to placebo received infliximab at weeks 14, 16 and 20 whereas patients randomized to infliximab received additional infliximab infusions every 8 weeks until week 22. Results Twenty four (24) patients were randomized in this study. At week 14, 33.3% and 66.7% of patients treated with infliximab achieved m‐PPPASI 75 and m‐PPPASI 50 respectively compared to 8.3% for both m‐PPPASI 75 (P = 0.317) and m‐PPPASI 50 (P = 0.009) for patients randomized to placebo. A reduction of 50.3% in the mean surface area of palms and soles affected with psoriasis was seen at week 14 in patients randomized to infliximab as compared to an increase of 14.9% in patients randomized to placebo (P = 0.009). Conclusions This pilot study did not reach its primary endpoint of m‐PPPASI 75 at week 14. However, infliximab was observed to be more efficacious than placebo in improving PPSA and with respect to the percentage of patients reaching m‐PPPASI 50 at week 14. Larger and longer term studies are needed for severe patients to better assess the efficacy of infliximab in palmoplantar psoriasis.     

From the Cover: PNAS Plus: Nicastrin functions to sterically hinder γ-secretase–substrate interactions driven by substrate transmembrane domain

γ-Secretase is an intramembrane-cleaving protease that processes many type-I integral membrane proteins within the lipid bilayer, an event preceded by shedding of most of the substrate’s ectodomain by α- or β-secretases. The mechanism by which γ-secretase selectively recognizes and recruits ectodomain-shed substrates for catalysis remains unclear. In contrast to previous reports that substrate is actively recruited for catalysis when its remaining short ectodomain interacts with the nicastrin component of γ-secretase, we find that substrate ectodomain is entirely dispensable for cleavage. Instead, γ-secretase–substrate binding is driven by an apparent tight-binding interaction derived from substrate transmembrane domain, a mechanism in stark contrast to rhomboid—another family of intramembrane-cleaving proteases. Disruption of the nicastrin fold allows for more efficient cleavage of substrates retaining longer ectodomains, indicating that nicastrin actively excludes larger substrates through steric hindrance, thus serving as a molecular gatekeeper for substrate binding and catalysis.Regulated intramembrane proteolysis (RIP) involves the cleavage of a wide variety of integral membrane proteins within their transmembrane domains (TMDs) by a highly diverse family of intramembrane-cleaving proteases (I-CLiPs) (1). I-CLiPs are found in all forms of life and govern many important biological functions, including but not limited to organism development (2), lipid homeostasis (3), the unfolded protein response (4), and bacterial quorum sensing (5). As the name implies, RIP must be tightly regulated to ensure that the resultant signaling events occur only when prompted by the cell and to prevent cleavage of the many nonsubstrate “bystander” proteins present within cellular membranes. Despite this, very little is known about the molecular mechanisms by which I-CLiPs achieve their exquisite specificity. Although traditional soluble proteases maintain substrate specificity by recognizing distinct amino acid sequences flanking the scissile bond, substrates for intramembrane proteases have little to no sequence similarity.Recent work on rhomboid proteases has demonstrated that this family of I-CLiPs achieves substrate specificity via a mechanism that is dependent on the transmembrane dynamics of the substrate rather than its sequence of amino acids (6, 7). Here, rhomboid possesses a very weak binding affinity for substrate and, in a rate-driven reaction, only cleaves those substrates that have unstable TMD helices that have had time to unfold into the catalytic active site, where they are cleaved before they can dissociate from the enzyme–substrate complex. Although it may be tempting to speculate that this is a conserved mechanism for all I-CLiPs, rhomboid is the only family of I-CLiPs that does not require prior activation of substrate through an initial cleavage by another protease (8). Specifically, site-2 protease substrates must be first cleaved by site-1 protease (9), signal peptide peptidase substrates are first cleaved by signal peptidase (10), and ectodomain shedding by α- or β-secretase is required before γ-secretase cleavage of its substrates (11, 12). These facts suggest that the diverse families of I-CLiPs likely have evolved fundamentally different mechanisms by which they recognize and cleave their substrates.Presenilin/γ-secretase is the founding member of the aspartyl family of I-CLiPs. The importance of γ-secretase function in biology and medicine is highlighted by its cleavage of the notch family of receptors, which is required for cell fate determination in all metazoans (2, 13–16), and of the amyloid precursor protein (APP), which is centrally implicated in Alzheimer’s disease (AD) (14, 17). In addition to APP and notch, γ-secretase has over 90 other reported substrates, many of which are involved in important signaling events (12, 18). Despite this, little is known about the mechanism by which γ-secretase binds and cleaves its substrates. Currently, the only known prerequisite for a substrate to be bound and hydrolyzed by γ-secretase is that it be a type-I integral membrane protein that first has most of its ectodomain removed by a sheddase, either α- or β-secretases (11, 12, 19). How γ-secretase selectively recognizes ectodomain-shed substrates and recruits them for catalysis while at the same time preventing cleavage of nonsubstrates remains unsettled.γ-Secretase is a multimeric complex composed of four integral membrane proteins both necessary and sufficient for full activity: presenilin, nicastrin, Aph-1, and Pen-2 (20–24). Presenilin is the proteolytic component, housing catalytic aspartates on TMDs 6 and 7 of its nine TMDs (17, 25, 26). After initial complex formation, the mature proteolytically active complex is formed when presenilin undergoes auto-proteolysis, resulting in N- and C-terminal fragments (NTF and CTF, respectively) (17, 27, 28), a process thought to be stimulated by the three-TMD component Pen-2 (29). The seven-TMD protein Aph-1 is believed to play a scaffolding role in complex formation (30, 31). Nicastrin is a type-I integral membrane protein with a large, heavily glycosylated ectodomain (32–34) that contains multiple stabilizing disulfide bridges (24, 34).The ectodomain of nicastrin is structurally homologous to a bacterial amino peptidase (34). Although nicastrin lacks the specific amino acids required for peptidase activity, it has been proposed to bind the N terminus of ectodomain-shed substrate, thereby directing substrate TMD to the γ-secretase active site for cleavage (35, 36). This mechanism has been suggested to depend on a key binding interaction between the free amine at the N terminus of the shortened substrate ectodomain and E333 of the vestigial amino peptidase domain of nicastrin (35, 36). However, the importance of nicastrin in substrate recognition has been questioned (37, 38), and although an initial high-resolution structure of γ-secretase suggested a role for nicastrin in substrate recognition (24), the most recent structures of the γ-secretase complex and the nicastrin ectodomain reveal that E333 is actually buried within the interior of nicastrin and resides on the opposite side of the complex relative to the active site (39, 40). Although this makes it unlikely that nicastrin is involved in direct substrate binding barring a large, energy-intensive conformational change, the basic mechanism of substrate recognition by γ-secretase remains controversial and requires resolution.Here, we demonstrate that nicastrin functions to sterically exclude substrates based on ectodomain size rather than actively recruit them for catalysis. This blocking mechanism allows γ-secretase to distinguish substrate from nonsubstrate and explains why substrate ectodomain shedding by α- or β-secretases is a prerequisite for γ-secretase catalysis. In contrast to rhomboid, γ-secretase apparently binds substrate TMD tightly, making the nicastrin steric hindrance mechanism necessary to prevent cleavage of nonectodomain-shed substrates and nonsubstrates alike.     

Mosaicism for Dominant Collagen 6 Mutations as a Cause for Intrafamilial Phenotypic Variability

Collagen 6‐related dystrophies and myopathies (COL6‐RD) are a group of disorders that form a wide phenotypic spectrum, ranging from severe Ullrich congenital muscular dystrophy, intermediate phenotypes, to the milder Bethlem myopathy. Both inter‐ and intrafamilial variable expressivity are commonly observed. We present clinical, immunohistochemical, and genetic data on four COL6‐RD families with marked intergenerational phenotypic heterogeneity. This variable expression seemingly masquerades as anticipation is due to parental mosaicism for a dominant mutation, with subsequent full inheritance and penetrance of the mutation in the heterozygous offspring. We also present an additional fifth simplex patient identified as a mosaic carrier. Parental mosaicism was confirmed in the four families through quantitative analysis of the ratio of mutant versus wild‐type allele (COL6A1, COL6A2, and COL6A3) in genomic DNA from various tissues, including blood, dermal fibroblasts, and saliva. Consistent with somatic mosaicism, parental samples had lower ratios of mutant versus wild‐type allele compared with the fully heterozygote offspring. However, there was notable variability of the mutant allele levels between tissues tested, ranging from 16% (saliva) to 43% (fibroblasts) in one mosaic father. This is the first report demonstrating mosaicism as a cause of intrafamilial/intergenerational variability of COL6‐RD, and suggests that sporadic and parental mosaicism may be more common than previously suspected.     

Oxidative stress-dependent MMP-13 activity underlies glucose neurotoxicity

Background

A complication of diabetes is neuropathy, a condition of sensory axon degeneration that originates in the epidermis. The mechanisms remain unknown but reactive oxygen species (ROS) have been implicated in this condition. In this study, we assessed the role of ROS and a candidate downstream target, MMP-13 in glucose-induced sensory axon degeneration in zebrafish and mice.

Adipose‐derived stromal cells for the reconstruction of a human vesical equivalent

Despite a wide panel of tissue‐engineering models available for vesical reconstruction, the lack of a differentiated urothelium remains their main common limitation. For the first time to our knowledge, an entirely human vesical equivalent, free of exogenous matrix, has been reconstructed using the self‐assembly method. Moreover, we tested the contribution of adipose‐derived stromal cells, an easily available source of mesenchymal cells featuring many potential advantages, by reconstructing three types of equivalent, named fibroblast vesical equivalent, adipose‐derived stromal cell vesical equivalent and hybrid vesical equivalent – the latter containing both adipose‐derived stromal cells and fibroblasts. The new substitutes have been compared and characterized for matrix composition and organization, functionality and mechanical behaviour. Although all three vesical equivalents displayed adequate collagen type I and III expression, only two of them, fibroblast vesical equivalent and hybrid vesical equivalent, sustained the development of a differentiated and functional urothelium. The presence of uroplakins Ib, II and III and the tight junction marker ZO‐1 was detected and correlated with impermeability. The mechanical resistance of these tissues was sufficient for use by surgeons. We present here in vitro tissue‐engineered vesical equivalents, built without the use of any exogenous matrix, able to sustain mechanical stress and to support the formation of a functional urothelium, i.e. able to display a barrier function similar to that of native tissue. Copyright © 2013 John Wiley & Sons, Ltd.