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  • Harris Baker posted an update 1 month, 1 week ago

    Our data suggest that Plin2 deficiency prevents these alcohol mediated effects on glucose tolerance. Our future studies will investigate specific mechanisms by which Plin2 deficiency protects against pancreatic beta cell dysfunction and glucose intolerance. Bioactive lipid metabolites can impair insulin signaling. In ALD, ceramides accumulate in the livers of both humans and rodents with ALD and are implicated in disease severity. Ceramide biosynthesis and metabolism is complex and involves three major synthetic pathways and metabolism to other sphingolipid species. Through mechanisms that are incompletely understood, ceramide accumulation results in activation of protein phosphatase 2A and subsequent inhibition of AKT phosphorylation, thereby impairing insulin signaling. The ceramide precursor sphingomyelin is a component of the lipid droplet membrane and the production of ceramide from sphingomyelin hydrolysis is implicated in alcohol’s impairment of glucose homeostasis. Here, we show a predominance of C16, C16.1, C22, C24 and C24:1 ceramides with alcohol-feeding. Little is known about the role of specific ceramide species in ALD, but reduction of C24 in alcohol fed mice has been shown to improve hepatic steatosis. Studies in other disease states have shown that C22 may have anti-proliferative properties ; C24 and C24:1 have pro-proliferative properties ; and C16 may promote apoptosis, thus its accumulation may conceivably promote alcohol-induced hepatotoxicity. Pharmacologic inhibition of ceramide de novo synthesis with myriocin improves hepatic insulin signaling in Long-Evans rats chronically fed alcohol and we previously reported that the onset of hepatic steatosis and insulin resistance in experimental ALD temporally correlates with an increase in long-chain hepatic ceramides and upregulation of Plin2. Our current results show that the increases in hepatic ceramides are prevented in the absence of Plin2 suggesting that Plin2 may mediate both cellular ceramide metabolism and insulin resistance in ALD, thus making Plin2 a potential target for therapy and/or prevention of ALD. In summary, alcohol-fed Plin2KO mice are protected from hepatic steatosis, glucose intolerance and hepatic ceramide accumulation. These results suggest a distinct role of Plin2 in the pathogenesis of ALD and ceramide metabolism and highlight the importance of additional studies to understand the specific mechanisms that link Plin2 to the pathogenesis of ALD. Future studies will additionally investigate the role of Plin2 in advanced stages of alcoholic liver disease. Etiology and progression of several neurodegenerative diseases including Alzheimer’s, Parkinson’s, Huntington’s and prion diseases are linked to the accumulation of protein aggregates in the form of large amyloid fibrils/plaques, or small oligomers or fibrillar fragments. According to the prevailing opinion, oligomers or small fibrillar fragments are the most toxic species and are responsible for the impairment of cellular functions, whereas mature fibrils or plaques are considered to be protective. Small soluble oligomers could be produced as prefibrillar intermediates on the pathway to mature amyloid fibrils, as a result of fragmentation of mature fibrils or large aggregates, or as off-pathway products formed through alternative aggregation mechanisms. Small oligomeric PrP particles produced by sonication from large pathogenic aggregates of the prion protein were found to exhibit the highest specific prion infectivity. Aggregation of mature fibrils into deposits and plaques is considered to be a protective mechanism that evolved in nature to avoid the high intrinsic toxicity of soluble oligomers or small fibrillar fragments. Defining the relationship between size, molecular architecture and toxicity of protein aggregates is essential for developing effective strategies for therapeutic intervention against neurodegenerative diseases. The current studies were designed to test the hypothesis about the relationship between prion protein fibril dimension and their cytotoxic potential and specifically, to address the question of whether fragmentation of fibrils into smaller fragments or oligomers always enhances toxic potential. To address this question, two conformationally different fibrillar amyloid states referred to as Rand S-fibrils were produced from highly-pure, full-length Syrian hamster rPrP. The cytotoxic potential of intact fibrils and small fibrillar fragments generated by sonication was tested using cultured cells. For one amyloid state, fibril fragmentation was found to enhance its cytotoxic potential, whereas for another amyloid state formed within the same amino acid sequence, the fragmented fibrils were found to be less toxic than the intact fibrils. These studies show that molecular structure of the amyloid state controls the relationship between fibrillar size and toxicity. The R- and S-fibrils were formed from full-length rPrP encompassing residues 23-231 under identical solvent conditions but different agitation modes as previously described. To examine the relationship between physical size and cytotoxicity, R- and S-fibrils were fragmented using a well-controlled sonication procedure, and toxicities of intact and fragmented fibrils were tested using cultured cells. Importantly, after sonication, R- and S-amyloid states preserved their individual Sor R-specific conformations despite smaller particle size. In our previous study, the cells of non-neuronal origin were found to exhibit the same ranking order in their susceptibility with respect to the toxic effect of different rPrP isoforms as cells of neuronal origin. Because the toxic effects of extracellular PrP aggregates is known to be mediated by a surface-expressed PrPC, in choosing the cell lines for the current study we were guided by the range of PrPC expression but not by the cell type. We chose two SKMEL cell lines, SKMEL-2 and SKMEL-28 that express PrPC at very low or high levels, respectively.