Proteopathic tau seeding predicts tauopathy in vivo

Transcellular propagation of protein aggregates, or proteopathic seeds, may drive the progression of neurodegenerative diseases in a prion-like manner. In tauopathies such as Alzheimer’s disease, this model predicts that tau seeds propagate pathology through the brain via cell–cell transfer in neural networks. The critical role of tau seeding activity is untested, however. It is unknown whether seeding anticipates and correlates with subsequent development of pathology as predicted for a causal agent. One major limitation has been the lack of a robust assay to measure proteopathic seeding activity in biological specimens. We engineered an ultrasensitive, specific, and facile FRET-based flow cytometry biosensor assay based on expression of tau or synuclein fusions to CFP and YFP, and confirmed its sensitivity and specificity to tau (∼300 fM) and synuclein (∼300 pM) fibrils. This assay readily discriminates Alzheimer’s disease vs. Huntington''s disease and aged control brains. We then carried out a detailed time-course study in P301S tauopathy mice, comparing seeding activity versus histological markers of tau pathology, including MC1, AT8, PG5, and Thioflavin S. We detected robust seeding activity at 1.5 mo, >1 mo before the earliest histopathological stain. Proteopathic tau seeding is thus an early and robust marker of tauopathy, suggesting a proximal role for tau seeds in neurodegeneration.Protein aggregation characterizes many neurodegenerative disorders, including Alzheimer’s disease (AD) and the related tauopathies. These disorders feature the accumulation of fibrillar deposits of the microtubule-associated protein tau with progressive deterioration of the central nervous system. Tau pathology and its associated brain atrophy do not appear randomly throughout the brain, but rather progress along distinct neural networks (1–5). This aspect suggests a role for transcellular spread of a pathogenic agent via neural connections. Our laboratory and others have previously hypothesized that tau aggregates—or seeds—serve as this agent of spread, transmitting the aggregated state from cell to cell via prion-like mechanisms (6–15).Mounting fundamental insights support this hypothesis. Tau seeds applied to the outside of cells bind the cell surface by attaching to heparan sulfate proteoglycans, triggering uptake by macropinocytosis (13). Upon internalization, tau seeds nucleate the fibrillization of endogenous tau monomer via templated conformational change, or seeding (8, 10). Tau seeding requires a critical unit of size for activity, as only particular species propagate the aggregated state (16). In vivo studies have described tau protein spreading from local sites to distant regions, presumably via transsynaptic movement (11, 12, 17–19). Finally, our laboratory and another recently demonstrated that tau propagates discrete amyloid conformations through the brains of animals that give rise to unique neuropathologies (18, 20).Despite this evidence, it remains unclear whether the development of proteopathic tau seeding represents a causal process of tauopathy, a downstream consequence of tau fibril accumulation, a coincident trait of neurodegeneration, or even an epiphenomenon. If proteopathic seeds are indeed a causal agent of disease, then their activity should exist in the brains of tauopathy mouse models and human subjects, precede other forms of pathology, and correlate with disease progression.To test these hypotheses, we created a highly sensitive and quantitative assay using a novel FRET-based biosensor cell line that specifically reports tau seeding activity. With this assay, we profiled the temporal evolution of tau seeding activity in the brains of P301S transgenic mice, a model of human tauopathy, and compared it to standard measurements of histopathology taken from the same animals. We find that tau seeding marks incipient tauopathy, occurring far before the onset of several standard histopathological markers. This finding implicates proteopathic tau seeding as a proximal cause of neurodegeneration, and establishes a highly quantitative and sensitive seed detection method.     

Muscle structural,energetic and functional benefits of endurance exercise training in sickle cell disease

Sickle cell disease (SCD) patients display skeletal muscle hypotrophy, altered oxidative capacity, exercise intolerance and poor quality of life. We previously demonstrated that moderate-intensity endurance training is beneficial for improving muscle function and quality of life of patients. The present study evaluated the effects of this moderate-intensity endurance training program on skeletal muscle structural and metabolic properties. Of the 40 randomized SCD patients, complete data sets were obtained from 33. The training group (n = 15) followed a personalized moderate-intensity endurance training program, while the non-training (n = 18) group maintained a normal lifestyle. Biopsies of the vastus lateralis muscle and submaximal incremental cycling tests were performed before and after the training program. Endurance training increased type I muscle fiber surface area (P = .038), oxidative enzyme activity [citrate synthase, P < .001; β-hydroxyacyl-CoA dehydrogenase, P = .009; type-I fiber cytochrome c oxidase, P = .042; respiratory chain complex IV, P = .017] and contents of respiratory chain complexes I (P = .049), III (P = .005), IV (P = .003) and V (P = .002). Respiratory frequency, respiratory exchange ratio, blood lactate concentration and rating of perceived exertion were all lower at a given submaximal power output after training vs non-training group (all P < .05). The muscle content of proteins involved in glucose transport and pH regulation were unchanged in the training group relative to the non-training group. The moderate-intensity endurance exercise program improved exercise capacity and muscle structural and oxidative properties. This trial was registered at www.clinicaltrials.gov as #NCT02571088.     

Giant squamous cell carcinoma as a complication of a chronic enterocutaneous fistula: complex parietal reconstruction

Treatment of an enterocutaneous fistula is complex and may require multidisciplinary management, especially when associated with a neoplastic process. Here, we describe the case of a 59‐year‐old patient with a squamous cell carcinoma that had invaded the abdominal wall through a chronic enterocutaneous fistula identified 30 years ago. We combined parietectomy with small intestine and colon resection and inguinal lymphadenectomy in order to obtain clear surgical margins. At the same time, plastic surgery involved the implementation of a large bioprosthesis and coverage with a vastus lateralis muscle free flap.     

Lead Exposure,B Vitamins,and Plasma Homocysteine in Men 55 Years of Age and Older: The VA Normative Aging Study

Background: Lead (Pb) exposure may influence the plasma concentration of homocysteine, a one-carbon metabolite associated with cardiovascular and neurodegenerative diseases. Little is known about the associations between Pb and homocysteine over time, or the potential influence of dietary factors.Objectives: We examined the longitudinal association of recent and cumulative Pb exposure with homocysteine concentrations and the potential modifying effect of dietary nutrients involved in one-carbon metabolism.Methods: In a subcohort of the Veterans Affairs (VA) Normative Aging Study (1,056 men with 2,301 total observations between 1993 and 2011), we used mixed-effects models to estimate differences in repeated measures of total plasma homocysteine across concentrations of Pb in blood and tibia bone, assessing recent and cumulative Pb exposure, respectively. We also assessed effect modification by dietary intake and plasma concentrations of folate, vitamin B₆, and vitamin B₁₂.Results: An interquartile range (IQR) increment in blood Pb (3 μg/dL) was associated with a 6.3% higher homocysteine concentration (95% CI: 4.8, 7.8%). An IQR increment in tibia bone Pb (14 μg/g) was associated with a 3.7% higher homocysteine (95% CI: 1.6, 5.6%), which was attenuated to 1.5% (95% CI: –0.5, 3.6%) after adjusting for blood Pb. For comparison, a 5-year increase in time from baseline was associated with a 5.7% increase in homocysteine (95% CI: 4.3, 7.1%). The association between blood Pb and homocysteine was significantly stronger among participants with estimated dietary intakes of vitamin B₆ and folate below (vs. above) the study population medians, which were similar to the U.S. recommended dietary allowance intakes.Conclusions: Pb exposure was positively associated with plasma homocysteine concentration. This association was stronger among men with below-median dietary intakes of vitamins B₆ and folate. These findings suggest that increasing intake of folate and B₆ might reduce Pb-associated increases in homocysteine, a risk factor for cardiovascular disease and neurodegeneration.Citation: Bakulski KM, Park SK, Weisskopf MG, Tucker KL, Sparrow D, Spiro A III, Vokonas PS, Nie LH, Hu H, Weuve J. 2014. Lead exposure, B vitamins, and plasma homocysteine in men 55 years of age and older: the VA Normative Aging Study. Environ Health Perspect 122:1066–1074; http://dx.doi.org/10.1289/ehp.1306931