Cytochrome P450 lanosterol 14alpha-demethylase (CYP51) and its products meiosis-activating sterols (MAS) were hypothesized by previous in vitro studies to have an important role in regulating meiosis and reproduction. To test this in vivo we generated a conditional male germ cell-specific knockout of the gene Cyp51 in the mouse. High excision efficiency of Cyp51 allele in germ cells resulted in 85-89% downregulation of Cyp51 mRNA and protein levels in germ cells. Quantitative metabolic profiling revealed significantly higher levels of CYP51 substrates lanosterol and 24,25-dihydrolanosterol and substantially diminished levels of MAS, the immediate products of CYP51. However, germ cell-specific ablation of Cyp51, leading to lack of MAS, did not affect testicular morphology, daily sperm production or reproductive performance in males. It is plausible that due to the similar structures of cholesterol intermediates, previously proposed biological function of MAS in meiosis progression can be replaced by some other yet unidentified functionally redundant lipid molecule(s). Our results using the germ cell-specific knockout model provides first in vivo evidence that the de novo synthesis of MAS and cholesterol in male germ cells is most likely not essential for spermatogenesis and reproduction and that MAS, originating from germ cells do not cell-autonomously regulate spermatogenesis and fertility.
COBISS.SI-ID: 30524121
Antley-Bixler syndrome (ABS) represents a group of heterogeneous disorders characterized by skeletal, cardiac and urogenital abnormalities that have frequently been associated with mutations in fibroblast growth factor receptor2 or cytochrome P450 reductase genes. In some ABS patients, reduced activity of the cholesterogenic cytochrome P450 CYP51A1, an ortholog of the mouse CYP51, and accumulation of lanosterol and 24,25-dihydrolanosterol has been reported, but the role of CYP51A1 in the ABS etiology has remained obscure. To test whether Cyp51 could be involved in generating an ABS-like phenotype, a mouse knockout model was developed that exhibited several prenatal ABS-like features leading to lethality at embryonic day 15. Cyp51(-/-) mice had no functional Cyp51 mRNA and no immunodetectable CYP51 protein. The two CYP51 enzyme substrates (lanosterol and 24,25-dihydrolanosterol) were markedly accumulated. Cholesterol precursors downstream of the CYP51 enzymatic step were not detected, indicating that the targeting in this study blocked de novo cholesterol synthesis. This was reflected in the up-regulation of 10 cholesterol synthesis genes, with the exception of 7-dehydrocholesterol reductase. Lethality was ascribed to heart failure due to hypoplasia, ventricle septum, epicardial and vasculogenesis defects, suggesting that Cyp51 deficiency was involved in heart development and coronary vessel formation. As the most likely downstream molecular mechanisms, alterations were identified in the sonic hedgehog and retinoic acid signaling pathways. Cyp51 knockout mice provide evidence that Cyp51 is essential for embryogenesis and present a potential animal model for studying ABS syndrome in humans.
COBISS.SI-ID: 28610009
This review describes the mouse knockout models of cholesterol synthesis, together with human malformations and drugs that target cholesterogenic enzymes. Generally, the sooner a gene acts in cholesterol synthesis, the earlier the phenotype occurs. Humans with loss of function of early cholesterogenic enzymes have not yet been described, and in the mouse, loss of Hmgcr is preimplantation lethal. Together, these results indicate that the widely prescribed cholesterol-lowering strains are potentially teratogenic. The Mvk knockout is early embrionic lethal in the mouse, the absence of Fdft 1 is lethal at E9.5-12.5 dpc, while the Cyp51 knockouts die at 15.5 dpc. Fungal CYP51 inhibitorazoles are teratogenic in humans, potentially leading to symptoms of Antley-Bixler syndrome. The X-linked mutations in Nsdhl and Ebp are embryonic lethal in male mice, while heterozygous females are also affected. Consequently the anticancer drugs, tamoxifen and toremifene, inhibiting human EBP, may be harmful in early pregnancy. The Dhcr7 and Dhcr24 knockout mice die shortly after birth, while humans survive with Smith-Lemli-Opitz syndrome or desmosterolosis. Since cholesterol is essential for hedgehog signaling, disturbance of this pathway by antipsychotics and -depressants explains some drug side effects. In conclusion, defects in cholesterol synthesis are generally lethal in mice, while humans with impairedlater steps of the pathway can survive with severe malformations. Evidence shows that drugs targeting or, by coincidence, inhibiting human cholesterol synthesis are better avoided in early pregnancy. Since drugs with teratogenic potential are successfully on the market, this should also be keptin mind in new cholesterol-related drug development.
COBISS.SI-ID: 2789256
Mammalian spermatogenesis is a complex developmental program in which a diploid progenitor germ cell transforms into highly specialized spermatozoa. One intriguing aspect of sperm production is the dynamic change in membrane lipid composition that occurs throughout spermatogenesis. Cholesterol content, as well as its intermediates, differs vastly between the male reproductive system and nongonadal tissues. Accumulation of cholesterol precursors such as testis meiosis-activating sterol and desmosterol is observed in testes and spermatozoa from several mammalian species. Moreover, cholesterogenic genes, especially meiosis-activating sterol-producing enzyme cytochrome P450 lanosterol 14 alpha-demethylase, display stage-specific expression patterns during spermatogenesis. Discrepancies in gene expression patterns suggest a complex temporal and cell-type specific regulation of sterol compounds during spermatogenesis, which also involves dynamic interactions between germ and Sertoli cells. The functional importance of sterol compounds in sperm production is further supported by the modulation of sterol composition in spermatozoal membranes during epididymal transit and in the female reproductive tract, which is a prerequisite for successful fertilization. However, the exact role of sterols in male reproduction is unknown. This review discusses sterol dynamics in sperm maturation and describes recent methodological advances that will help to illuminate the complexity of sperm formation and function.
COBISS.SI-ID: 3134600
Mice deficient in the nuclear hormone receptor ROR[gamma]t have defective development of thymocytes, lymphoid organs, Th17 cells, and type 3 innate lymphoid cells. ROR[gamma]t binds to oxysterols derived from cholesterol catabolism, but it is not clear whether these are its natural ligands. Here, we show that sterol lipids are necessary and sufficient to drive ROR[gamma]t-dependent transcription. We combined overexpression, RNAi, and genetic deletion of metabolic enzymes to study ROR[gamma]-dependent transcription. Our results are consistent with the ROR[gamma]t ligand(s) being a cholesterol biosynthetic intermediate (CBI) downstream of lanosterol and upstream of zymosterol. Analysis of lipids bound to ROR[gamma] identified molecules with molecular weights consistent with CBIs. Furthermore, CBIs stabilized the ROR[gamma] ligand-binding domain and induced coactivator recruitment. Genetic deletion of metabolic enzymes upstream of the ROR[gamma]t-ligand(s) affected the development of lymph nodes and Th17 cells. Our data suggest that CBIs play a role in lymphocyte development potentially through regulation of ROR[gamma].
COBISS.SI-ID: 3506824