The essential role of adenine nucleotide translocase 4 on male reproductive function in mice.

Adenine nucleotide translocator 4 (Ant4), an ATP/ADP transporter expressed in the early phases of spermatogenesis, plays a crucial role in male fertility. While Ant4 loss causes early arrest of meiosis and increased apoptosis of spermatogenic cells in male mice, its other potential functions in male fertility remain unexplored. Here, we utilized Ant4 knockout mice to delineate the effects of Ant4-deficiency on male reproduction. Our observations demonstrated that Ant4-deficiency led to infertility and impaired testicular development, which was further investigated by evaluating testicular oxidative stress, autophagy, and inflammation. Specifically, the loss of Ant4 led to an imbalance of oxidation and antioxidants. Significant ultrastructural alterations were identified in the testicular tissues of Ant4-deficient mice, including swelling of mitochondria, loss of cristae, and accumulation of autophagosomes. Our results also showed that autophagic flux and AKT-AMPK-mTOR signaling pathway were affected in Ant4-deficient mice. Moreover, Ant4 loss increased the expression of pro-inflammatory factors. Overall, our findings underscored the importance of Ant4 in regulating oxidative stress, autophagy, and inflammation in testicular tissues. Taken together, these insights provided a nuanced understanding of the significance of Ant4 in testicular development.

Glutamine prevents high-fat diet-induced hepatic lipid accumulation in mice by modulating lipolysis and oxidative stress.

Metabolic-associated fatty liver disease (MAFLD) is related to metabolic dysfunction and is characterized by excess fat storage in the liver. Several studies have indicated that glutamine could be closely associated with lipid metabolism disturbances because of its important role in intermediary metabolism. However, the effect of glutamine supplementation on MAFLD progression remains unclear. Here, we used a high-fat diet (HFD)-induced MAFLD C57BL/6 mouse model, and glutamine was supplied in the drinking water at different time points for MAFLD prevention and reversal studies. A MAFLD prevention study was performed by feeding mice an HFD concomitant with 4% glutamine treatment for 24 weeks, whereas the MAFLD reversal study was performed based on 4% glutamine treatment for 13 weeks after feeding mice an HFD for 10 weeks. In the prevention study, glutamine treatment ameliorated serum lipid storage, hepatic lipid injury, and oxidative stress in HFD-induced obese mice, although glutamine supplementation did not affect body weight, glucose homeostasis, energy expenditure, and mitochondrial function. In the MAFLD reversal study, there were no noticeable changes in the basic physiological phenotype and hepatic lipid metabolism. In summary, glutamine might prevent, but not reverse, HFD-induced MAFLD in mice, suggesting that a cautious attitude is required regarding its use for MAFLD treatment.

The essential role of adenine nucleotide translocase 4 on male reproductive function in mice

Adenine nucleotide translocator 4 (Ant4), an ATP/ADP transporter expressed in the early phases of spermatogenesis, plays a crucial role in male fertility. While Ant4 loss causes early arrest of meiosis and increased apoptosis of spermatogenic cells in male mice, its other potential functions in male fertility remain unexplored. Here, we utilized Ant4 knockout mice to delineate the effects of Ant4-deficiency on male reproduction. Our observations demonstrated that Ant4-deficiency led to infertility and impaired testicular development, which was further investigated by evaluating testicular oxidative stress, autophagy, and inflammation. Specifically, the loss of Ant4 led to an imbalance of oxidation and antioxidants. Significant ultrastructural alterations were identified in the testicular tissues of Ant4-deficient mice, including swelling of mitochondria, loss of cristae, and accumulation of autophagosomes. Our results also showed that autophagic flux and AKT-AMPK-mTOR signaling pathway were affected in Ant4-deficient mice. Moreover, Ant4 loss increased the expression of pro-inflammatory factors. Overall, our findings underscored the importance of Ant4 in regulating oxidative stress, autophagy, and inflammation in testicular tissues. Taken together, these insights provided a nuanced understanding of the significance of Ant4 in testicular development.

Serine active site containing protein 1 depletion alters lipid metabolism and protects against high fat diet-induced obesity in mice.

OBJECTIVE: Although the serine active site containing 1 (SERAC1) protein is essential for cardiolipin remodeling and cholesterol transfer, its physiological role in whole-body energy metabolism remains unclear. Thus, we investigated the role of SERAC1 in lipid distribution and metabolism in mice. METHODS: CRISPR/Cas9 was used to create homozygous Serac1 knockout mice. A range of methods, including electron microscopy, histological analysis, DNA sequencing, glucose and insulin tolerance tests, and biochemical analysis of serum lipid levels, were used to assess lipid distribution and rates of lipid synthesis in mice. RESULTS: We found that Serac1 depletion in mice prevented high-fat diet-induced obesity but did not affect energy expenditure. The liver was affected by Serac1 depletion, but adipose tissues were not. Serac1 depletion was shown to impair cholesterol transfer from the liver to the serum and led to an imbalance in cholesterol distribution. The livers from mice with Serac1 depletion showed increased cholesterol synthesis because the levels of cholesterol synthesis enzymes were upregulated. Moreover, the accumulation of hepatic lipid droplets in mice with Serac1 depletion were decreased, suggesting that SERAC1 depletion may decrease the risk for hepatic steatosis in high fat diet-induced mice. CONCLUSION: Our findings demonstrate that SERAC1 can serve as a potential target for the treatment or prevention of diet-induced hepatic lipid metabolic disorders.

SERAC1 is a component of the mitochondrial serine transporter complex required for the maintenance of mitochondrial DNA.

SERAC1 deficiency is associated with the mitochondrial 3-methylglutaconic aciduria with deafness, (hepatopathy), encephalopathy, and Leigh-like disease [MEGD(H)EL] syndrome, but the role of SERAC1 in mitochondrial physiology remains unknown. Here, we generated Serac1-/- mice that mimic the major diagnostic clinical and biochemical phenotypes of the MEGD(H)EL syndrome. We found that SERAC1 localizes to the outer mitochondrial membrane and is a protein component of the one-carbon cycle. By interacting with the mitochondrial serine transporter protein SFXN1, SERAC1 facilitated and was required for SFXN1-mediated serine transport from the cytosol to the mitochondria. Loss of SERAC1 impaired the one-carbon cycle and disrupted the balance of the nucleotide pool, which led to primary mitochondrial DNA (mtDNA) depletion in mice, HEK293T cells, and patient-derived immortalized lymphocyte cells due to insufficient supply of nucleotides. Moreover, both in vitro and in vivo supplementation of nucleosides/nucleotides restored mtDNA content and mitochondrial function. Collectively, our findings suggest that MEGD(H)EL syndrome shares both clinical and molecular features with the mtDNA depletion syndrome, and nucleotide supplementation may be an effective therapeutic strategy for MEGD(H)EL syndrome.

GRP75 Regulates Mitochondrial-Supercomplex Turnover to Modulate Insulin Sensitivity.

GRP75 (75-kDA glucose-regulated protein), defined as a major component of both the mitochondrial quality control system and mitochondria-associated membrane, plays a key role in mitochondrial homeostasis. In this study, we assessed the roles of GRP75, other than as a component, in insulin action in both in vitro and in vivo models with insulin resistance. We found that GRP75 was downregulated in mice fed a high-fat diet (HFD) and that induction of Grp75 in mice could prevent HFD-induced obesity and insulin resistance. Mechanistically, GRP75 influenced insulin sensitivity by regulating mitochondrial function through its modulation of mitochondrial-supercomplex turnover rather than mitochondria-associated membrane communication: GRP75 was negatively associated with respiratory chain complex activity and was essential for mitochondrial-supercomplex assembly and stabilization. Moreover, mitochondrial dysfunction in Grp75-knockdown cells might further increase mitochondrial fragmentation, thus triggering cytosolic mtDNA release and activating the cGAS/STING-dependent proinflammatory response. Therefore, GRP75 can serve as a potential therapeutic target of insulin resistant-related diabetes or other metabolic diseases.