This article is available online at http://www.jlr.org Supplementary key words essential fatty acids • arachidonic acid • highly unsaturated fatty acids • very-long-chain polyunsaturated fatty acids • choelsta-3,5-diene • male reproduction • spermiogenesis Delta-6 desaturase (D6D) is the fi rst and rate-limiting enzyme for highly unsaturated fatty acid (HUFA) synthesis that consists of a series of elongation and desaturation reactions ( 1 ). The dietary essential fatty acids 18:2n-6 (linoleic acid) and 18:3n-3 ( ␣ -linolenic acid) are substrates for D6D and precursors of physiologically important HUFAs, such as 20:4n-6 [arachidonic acid (AA)], 22:5n6 [docosapentaenoic acid (DPAn6)], and 22:6n3 [docosahexaenoic acid (DHA)]. D6D is also required for the fi nal desaturation step for the synthesis of DPAn6 and DHA.These HUFAs are present in high concentration in testes and sperm of mammals. DPAn6, a HUFA derived from AA, dramatically increases in rat testes during the sexual maturation stage ( 2 ). In mice, AA, DPAn6, and DHA are abundant in membrane phospholipids of round spermatids ( 3 ) and mature mouse spermatozoa ( 4 ), suggesting an important role for these fatty acids for proper spermatogenesis. In humans, DHA is the main HUFA in sperm ( 5 ). DHA is specifi cally high in the sperm tail when compared with the sperm head in monkeys ( 6 ), implying a role of DHA in sperm tail function. AA may also have a role in male fertility as a precursor to eicosanoids. Prostaglandin E2, for example, has been shown to increase sperm motility ( 7 ), while inhibition of cycloxygenase-2 in mouse vas deferens results in a decrease of sperm motility and fertilAbstract Delta-6 desaturase-null mice ( ؊ / ؊ ) are unable to synthesize highly unsaturated fatty acids (HUFAs): arachidonic acid (AA), docosahexaenoic acid (DHA), and n6-docosapentaenoic acid (DPAn6). The ؊ / ؊ males exhibit infertility and arrest of spermatogenesis at late spermiogenesis. To determine which HUFA is essential for spermiogenesis, a diet supplemented with either 0.2% (w/w) AA or DHA was fed to wild-type ( Abbreviations: AA, arachidonic acid; CD, cholesta-3,5-diene; D6D, ⌬ 6 desaturase; DHA, docosahexaenoic acid; DPAn6, docosapentaenoic acid; FAME, fatty acid methyl esters; HUFA, highly unsaturated fatty acid; VLPUFA, very-long-chain polyunsaturated fatty acid.

Secondary bile acids have long been postulated to be tumor promoters in the colon; however, their mechanism of action remains unclear. In this study, we examined the actions of bile acids at the cell membrane and found that they can perturb membrane structure by alteration of membrane microdomains. Depletion of membrane cholesterol by treating with methyl-␤-cyclodextrin suppressed deoxycholic acid (DCA)-induced apoptosis, and staining for cholesterol with filipin showed that DCA caused a marked rearrangement of this lipid in the membrane. Likewise, DCA was found to affect membrane distribution of caveolin-1, a marker protein that is enriched in caveolae membrane microdomains. Additionally, fluorescence anisotropy revealed that DCA causes a decrease in membrane fluidity consistent with the increase in membrane cholesterol content observed after 4 h of DCA treatment of HCT116 cells. Significantly, by using radiolabeled bile acids, we found that bile acids are able to interact with and localize to microdomains differently depending on their physicochemical properties. DCA was also found to induce tyrosine phosphorylation and activate the receptor tyrosine kinase epidermal growth factor receptor in a ligand-independent manner. In contrast, ursodeoxycholic acid did not exhibit any of these effects even though it interacted significantly with the microdomains. Collectively, these data suggest that bile acid-induced signaling is initiated through alterations of the plasma membrane structure and the redistribution of cholesterol.

Apratoxin A is a natural product with potent antiproliferative activity against many human cancer cell lines. However, we and other investigators observed that it has a narrow therapeutic window in vivo. Previous mechanistic studies have suggested its involvement in the secretory pathway as well as the process of chaperone-mediated autophagy. Still the link between the biologic activities of apratoxin A and its in vivo toxicity has remained largely unknown. A better understanding of this relationship is critically important for any further development of apratoxin A as an anticancer drug. Here, we describe a detailed pathologic analysis that revealed a specific pancreas-targeting activity of apratoxin A, such that severe pancreatic atrophy was observed in apratoxin A-treated animals. Follow-up tissue distribution studies further uncovered a unique drug distribution profile for apratoxin A, showing high drug exposure in pancreas and salivary gland. It has been shown previously that apratoxin A inhibits the protein secretory pathway by preventing cotranslational translocation. However, the molecule targeted by apratoxin A in this pathway has not been well defined. By using a 3 H-labeled apratoxin A probe and specific Sec 61a/b antibodies, we identified that the Sec 61 complex is the molecular target of apratoxin A. We conclude that apratoxin A in vivo toxicity is likely caused by pancreas atrophy due to high apratoxin A exposure.

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Non-alcoholic fatty liver disease (NAFLD) is a progressive liver disease characterized by dysregulated lipid metabolism and chronic inflammation ultimately resulting in fibrosis. Untreated, NAFLD may progress to non-alcoholic steatohepatitis (NASH), cirrhosis and death. However, currently there are no FDA approved therapies that treat NAFLD/NASH. Thrombospondin-I (TSP-1) is a large glycoprotein in the extracellular matrix that regulates numerous cellular pathways including transforming growth factor beta 1 (TGF-β1) activation, angiogenesis, inflammation and cellular adhesion. Increased expression of TSP-1 has been reported in various liver diseases; however, its role in NAFLD/NASH is not well understood. We first examined TSP-1 modulation in hepatic stellate cell activation, a critical initiating step in hepatic fibrosis. Knockdown or inhibition of TSP-1 attenuated HSC activation measured by alpha smooth muscle actin (α-SMA) and Collagen I expression. To investigate the impact of TSP-1 modulation in context of NAFLD/NASH, we examined the effect of TSP-1 deficiency in the choline deficient L-amino acid defined high fat diet (CDAHFD) model of NASH in mice by assessing total body and liver weight, serum liver enzyme levels, serum lipid levels, liver steatosis, liver fibrosis and liver gene expression in wild type (WT) and TSP-1 null mice. CDAHFD fed mice, regardless of genotype, developed phenotypes of NASH, including significant increase in liver weight and liver enzymes, steatosis and fibrosis. However, in comparison to WT, CDAHFD-fed TSP-1 deficient mice were protected against numerous NASH phenotypes. TSP-1 null mice exhibited a decrease in serum lipid levels, inflammation markers and hepatic fibrosis. RNA-seq based transcriptomic profiles from the liver of CDAHFD fed mice determined that both WT and TSP-1 null mice exhibited similar gene expression signatures following CDAHFD, similar to biophysical and histological assessment comparison. Comparison of transcriptomic profiles based on genotype suggested that peroxisome proliferator activated receptor alpha (PPARα) pathway and amino acid metabolism pathways are differentially expressed in TSP-1 null mice. Activation of PPARα pathway was supported by observed decrease in serum lipid levels. Our findings provide important insights into the role of TSP-1 in context of NAFLD/NASH and TSP-1 may be a target of interest to develop anti-fibrotic therapeutics for NAFLD/NASH.