Testicular temperature-labile cholesteryl ester hydrolase. Relationship to isoenzymes from other tissues, correlation with spermatogenesis, and inhibition by physiological concentrations of divalent cations

Very long chain PUFA in murine testicular triglycerides and cholesterol esters

Very long chain (VLC) PUFA of the n-6 and n-3 series are known to occur in mammalian testis. The aim of this work was to characterize further two testicular lipid classes with VLCPUFA, cholesterol esters (CE) and total triglycerides (TG) in rat and mouse testis. The VLCPUFA predominating in these lipids were a series of n-6 pentaenes and tetraenes with 24 to 32 carbons, including small amounts of odd-chain PUFA, 28:5n-6 and 24:5n-6 prevailing in CE and TG, respectively. Most of the VLCPUFA of TG were concentrated in a small fraction of TG, made up by 1-O-alkyl-2,3-DAG. This TG subclass was absent altogether from the TG of sexually immature testis. The TG and the CE with VLCPUFA only occurred in testis of adult fertile animals. The proportion of VLCPUFA in total TG and CE was higher in rodents than in other mammals. In the n-6 PUFA-rich adult mouse testis, the amounts of testicular triacylglycerols decreased significantly after consumption of fish oil for 2 wk. Whereas 18:2n-6 was significantly reduced, the amounts of 22:5n-6 and longer n-6 PUFA were less affected in all major testicular lipids including PC and PE, where they were unchanged. The 1-O-alkyl-2,3-DAG and their n-6 VLCPUFA were virtually unaffected by the diet. The VLCPUFA-containing molecular species of CE and TG may represent a form of storage of cholesterol and polyenoic FA required to sustain spermatogenesis. Via chain-shortening, VLCPUFA stored in the neutral lipids may serve as precursors of the major C22 PUFA typical of cell membrane glycerophospholipids, protecting testicular cells against shifts in FA composition induced by dietary changes.

Targeted disruption of hormone-sensitive lipase results in male sterility and adipocyte hypertrophy, but not in obesity

Hormone-sensitive lipase (HSL) is known to mediate the hydrolysis not only of triacylglycerol stored in adipose tissue but also of cholesterol esters in the adrenals, ovaries, testes, and macrophages. To elucidate its precise role in the development of obesity and steroidogenesis, we generated HSL knockout mice by homologous recombination in embryonic stem cells. Mice homozygous for the mutant HSL allele (HSL-/-) were superficially normal except that the males were sterile because of oligospermia. HSL-/- mice did not have hypogonadism or adrenal insufficiency. Instead, the testes completely lacked neutral cholesterol ester hydrolase (NCEH) activities and contained increased amounts of cholesterol ester. Many epithelial cells in the seminiferous tubules were vacuolated. NCEH activities were completely absent from both brown adipose tissue (BAT) and white adipose tissue (WAT) in HSL-/- mice. Consistently, adipocytes were significantly enlarged in the BAT (5-fold) and, to a lesser extent in the WAT (2-fold), supporting the concept that the hydrolysis of triacylglycerol was, at least in part, impaired in HSL-/- mice. The BAT mass was increased by 1.65-fold, but the WAT mass remained unchanged. Discrepancy of the size differences between cell and tissue suggests the heterogeneity of adipocytes. Despite these morphological changes, HSL-/- mice were neither obese nor cold sensitive. Furthermore, WAT from HSL-/- mice retained 40% of triacylglycerol lipase activities compared with the wild-type WAT. In conclusion, HSL is required for spermatogenesis but is not the only enzyme that mediates the hydrolysis of triacylglycerol stored in adipocytes.

Immunological identification of cholesterol ester hydrolase in the steroidogenic tissues, adrenal glands and testis

Monoclonal antibodies were generated against the purified pancreatic cholesterol ester hydrolase (CEH, EC 3.1.1.13) to examine the expression of CEH in various bovine tissues. The presence of CEH isozyme antigenically indistinguishable from pancreatic enzyme in the steroidogenic tissues, adrenal glands and testis has been first demonstrated here using the immunoprecipitation method. These results suggest that CEH isozyme, similar to pancreatic CEH, might be involved in the cholesterol metabolism in the steroidogenic tissue.

Purification and characterization of a 28 kDa cytosolic inhibitor of cholesteryl ester hydrolases in rat testis

A 28 kDa inhibitory protein was purified from rat testis cytosol by sequential 40-65% ammonium sulfate precipitation, cation exchange chromatography, anion exchange chromatography, and preparative SDS-polyacrylamide gel electrophoresis. The heat-stable, trypsin-labile protein exhibited nonenzymatic, concentration-dependent inhibition of testicular and pancreatic cholesteryl ester hydrolases at all stages of purification. Copurifying at each stage was a 26.5 kDa protein which comprised 25% of the mass of the two proteins. Polyclonal antibodies raised to either or both 28 kDa and 26.5 kDa proteins by direct injection of excised electrophoretic bands cross-reacted with both proteins on western blots, immunoprecipitated both proteins, and neutralized inhibitory activity. Amino acid compositions of the individual proteins electroeluted from SDS-polyacrylamide gels were different from those of other surface-active proteins of similar molecular weights. Both proteins exhibited identical pl of 4.8 on chromatofocusing columns and two-dimensional gel electrophoresis. Although the subcellular distribution of the 28 kDa protein is unknown, its testicular cytosolic concentration, calculated from the purified protein mass, was 8 X 10(-9) mols/L, which probably underestimates the actual concentration by an order of magnitude. This is greater than the minimum concentration required for in vitro inhibition (10(-9) mols/L), consistent with a physiological role for this protein.

Localization of hormone-sensitive lipase to rat Sertoli cells and its expression in developing and degenerating testes

Using in situ hybridization, hormone-sensitive lipase was found to be expressed in a stage-dependent manner in Sertoli cells of rat testis. No expression was found in Leydig cells but expression in spermatids could not be excluded. These results suggest a role for hormone-sensitive lipase in the metabolism of lipid droplets in Sertoli cells, in contrast to its previously proposed function in steroid biosynthesis. The expression of testicular hormone-sensitive lipase mRNA and protein, both larger in size compared to other tissues, coincided with the onset of spermatogenesis and was dependent on scrotal localization of the testis, suggesting a temperature-dependent, pretranslational regulation of expression.