Expression of Synj2bp in mouse liver regulates the extent of wrappER-mitochondria contact to maintain hepatic lipid homeostasis.

BACKGROUND: In mouse liver hepatocytes, nearly half of the surface area of every mitochondrion is covered by wrappER, a wrapping-type of ER that is rich in fatty acids and synthesizes lipoproteins (VLDL) (Anastasia et al. in Cell Rep 34:108873, 2021; Hurtley in Science (80- ) 372:142-143, 2021; Ilacqua et al. in J Cell Sci 135:1-11, 2021). A disruption of the ultrastructure of the wrappER-mitochondria contact results in altered fatty acid flux, leading to hepatic dyslipidemia (Anastasia et al. 2021). The molecular mechanism that regulates the extent of wrappER-mitochondria contacts is unknown. METHODS: We evaluated the expression level of the mitochondrial protein Synj2bp in the liver of normal and obese (ob/ob) mice. In addition, we silenced its expression in the liver using an AAV8 vector. We coupled quantitative EM morphometric analysis to proteomics and lipid analyses on these livers. RESULTS: The expression level of Synj2bp in the liver positively correlates with the extent of wrappER-mitochondria contacts. A 50% reduction in wrappER-mitochondria contacts causes hepatic dyslipidemia, characterized by a gross accumulation of lipid droplets in the liver, an increased hepatic secretion of VLDL and triglycerides, a curtailed ApoE expression, and an increased capacity of mitochondrial fatty acid respiration. CONCLUSION: Synj2bp regulates the extent of wrappER-mitochondria contacts in the liver, thus contributing to the control of hepatic lipid flux.

Mitochondria-rough-ER contacts in the liver regulate systemic lipid homeostasis.

Contacts between organelles create microdomains that play major roles in regulating key intracellular activities and signaling pathways, but whether they also regulate systemic functions remains unknown. Here, we report the ultrastructural organization and dynamics of the inter-organellar contact established by sheets of curved rough endoplasmic reticulum closely wrapped around the mitochondria (wrappER). To elucidate the in vivo function of this contact, mouse liver fractions enriched in wrappER-associated mitochondria are analyzed by transcriptomics, proteomics, and lipidomics. The biochemical signature of the wrappER points to a role in the biogenesis of very-low-density lipoproteins (VLDL). Altering wrappER-mitochondria contacts curtails VLDL secretion and increases hepatic fatty acids, lipid droplets, and neutral lipid content. Conversely, acute liver-specific ablation of Mttp, the most upstream regulator of VLDL biogenesis, recapitulates this hepatic dyslipidemia phenotype and promotes remodeling of the wrappER-mitochondria contact. The discovery that liver wrappER-mitochondria contacts participate in VLDL biology suggests an involvement of inter-organelle contacts in systemic lipid homeostasis.

Association between expression of TNF-α, P53 and HIF1α with asthenozoospermia.

Reduced sperm motility (asthenozoospermia) accounts for a significant percentage of male infertility and numerous factors have been suggested to explain this phenomenon among which hypoxic and inflammatory markers are the least studied. Therefore, the aim of this study was to assess the main molecular markers involved in hypoxia (P53 and HIF-1α) and inflammation (TNF-α) pathways in infertile men with asthenozoospermia. Expression of these markers were assessed by qRT-PCR, and analysis of data show that mean of hypoxia markers (P53, HIF-1α) and also TNF- α were significantly higher in infertile men with asthenozoospermia compared to fertile men (p < 0.05). Unlike TNF-α, significant negative correlations were observed between expression of P53 (r = -0.568; p = 0.002) and HIF-1α (r = -0.403; p = 0.046) with sperm motility. In addition, a significant negative correlation was observed between expression of P53 with sperm concentration (r = -0.576; p < 0.001). In addition, a significant positive correlation was observed between hypoxia markers (P53, HIF-1α) and TNF-α (p < 0.01). However, no significant relation was observed between TNF-α and semen parameters. Taken together, the results of this study suggest the involvement of hypoxia pathway is more pronounced than the inflammatory pathway in asthenozoospermia.

Hypoxia pathway has more impact than inflammation pathway on etiology of infertile men with varicocele.

This study aimed to compare main molecular markers of hypoxia (HIF1-α and P53) and inflammation (TLR-2, TLR-4 and TNF-α) pathways between infertile men with varicocele and fertile individuals. Sperm parameters such as sperm concentration, motility and morphology were assessed according to World Health Organization (Laboratory manual for the examination and processing of human semen. Geneva, Switzerland, 2010) guideline in 20 infertile men with grade II or III varicocele, and 20 fertile men candidate of family balancing. In addition, sperm DNA fragmentation and molecular markers involved in hypoxia and inflammation pathways were evaluated by terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay and real-time PCR respectively. Mean of sperm parameters (concentration, motility and morphology) and DNA integrity were significantly lower in infertile men with varicocele compared to fertile individuals. Unlike markers involved in inflammation pathway, mean expression of markers of hypoxia pathway (HIF1-α and P53) was significantly higher in infertile men with varicocele compared to fertile individuals (p < 0.05), and also a significant correlation was observed between expression of HIF1-α and P53 (r = 0.461; p = 0.003). Overall, the result of this study suggests higher likelihood of involvement of hypoxia pathway, in comparison with inflammation pathway, in pathogenesis varicocele associated with male infertility.