Biology subjects

Sitcheran, R.

Publications and source records attributed to Sitcheran, R..

5 recordsLinked to original sources

bioRxiv2024

Glucose-6-phosphatase is required for sperm energy metabolism, motility and fertility in Drosophila

Glucose-6-Phosphatase (G6Pase), a key enzyme in gluconeogenesis and glycogenolysis in the mammalian liver and kidney, converts glucose-6-phosphate to glucose for maintaining systemic blood glucose homeostasis during nutrient deprivation. However, its function has remained elusive in insects, which have no need for G6Pase in sugar homeostasis since they convert glucose-6-phosphate to trehalose, their main circulating sugar, via trehalose phosphate synthase (TPS1). In this study we identify an unexpected and essential requirement for G6Pase in Drosophila male fertility, specifically to produce motile sperm. In G6P mutant males, spermatogenesis and spermiogenesis appear to proceed normally, leading to the production and transfer of mature sperm. However, once inside the female reproductive tract, G6P mutant sperm exhibit severely reduced tail beat frequency and only rarely enter an egg. Moreover, when compared to wild type sperm, G6P-deficient sperm are depleted more rapidly from the spermatheca and seminal receptacle, the female sperm storage organs. Immunohistochemical analyses show that G6P mutant spermatocytes present with an enlarged and stressed endoplasmic reticulum (ER) and a diminished Golgi apparatus. Additionally, the acrosome, a Golgi derived organelle that is critical for sperm capacitation, exhibits diminished expression of the transmembrane protein SNEAKY, which is essential to breakdown the sperm plasma membrane after fertilization. Metabolic analyses show impairment of both basal and compensatory glycolysis, as well as ATP production, in testes of G6P mutant males. Taken together, our investigations unveil a novel and crucial function for G6Pase in male fertility, highlighting its importance in regulating energy homeostasis in reproductive tissues.

cell biology↗

bioRxiv2024

Caspase-11 drives macrophage hyperinflammation in models of Polg-related mitochondrial disease

Mitochondrial diseases (MtD) represent a significant public health challenge due to their heterogenous clinical presentation, often severe and progressive symptoms, and lack of effective therapies. Environmental exposures, such bacterial and viral infection, can further compromise mitochondrial function and exacerbate the progression of MtD. Infections in MtD patients more frequently progress to sepsis, pneumonia, and other detrimental inflammatory endpoints. However, the underlying immune alterations that enhance immunopathology in MtD remain unclear, constituting a key gap in knowledge that complicates treatment and increases mortality in this vulnerable population. Here we employ in vitro and in vivo approaches to clarify the molecular and cellular basis for innate immune hyperactivity in models of polymerase gamma (Polg)-related MtD. We reveal that type I interferon (IFN-I)-mediated upregulation of caspase-11 and guanylate-binding proteins (GBPs) increase macrophage sensing of the opportunistic microbe Pseudomonas aeruginosa (PA) in Polg mutant mice. Furthermore, we show that excessive cytokine secretion and activation of pyroptotic cell death pathways contribute to lung inflammation and morbidity after infection with PA. Our work sheds new light on innate immune dysregulation in MtD and reveals potential targets for limiting infection- and inflammation-related complications in Polg-related MtD.

immunology↗

bioRxiv2024

Late-life dietary folate restriction reduces biosynthetic processes without compromising healthspan in mice

Folate is a vitamin required for cell growth and is present in fortified foods in the form of folic acid to prevent congenital abnormalities. The impact of low folate status on life-long health is poorly understood. We found that limiting folate levels with the folate antagonist methotrexate increased the lifespan of yeast and worms. We then restricted folate intake in aged mice and measured various health metrics, metabolites, and gene expression signatures. Limiting folate intake decreased anabolic biosynthetic processes in mice and enhanced metabolic plasticity. Despite reduced serum folate levels in mice with limited folic acid intake, these animals maintained their weight and adiposity late in life, and we did not observe adverse health outcomes. These results argue that the effectiveness of folate dietary interventions may vary depending on an individuals age and sex. A higher folate intake is advantageous during the early stages of life to support cell divisions needed for proper development. However, a lower folate intake later in life may result in healthier aging.

molecular biology↗

bioRxiv2022

NF-κB-Inducing Kinase (NIK) Governs the Mitochondrial Respiratory Capacity, Differentiation, and Inflammatory Status of Innate Immune Cells

NF-{kappa}B-Inducing Kinase (NIK), which is essential for the activation of the noncanonical NF-{kappa}B pathway, regulates diverse processes in immunity, development, and disease. While recent studies have elucidated important functions of NIK in adaptive immune cells and cancer cell metabolism, the role of NIK in metabolic-driven inflammatory responses in innate immune cells remains unclear. Here, we demonstrate that NIK-deficient bone marrow-derived macrophages exhibit defects in mitochondrial-dependent metabolism and oxidative phosphorylation (OXPHOS), which impairs the acquisition of a pro-repair, anti-inflammatory phenotype. Subsequently, NIK-deficient mice exhibit skewing of myeloid cells characterized by aberrant eosinophil, monocyte, and macrophage cell populations in the blood, bone marrow, and adipose tissue. Furthermore, NIK-deficient blood monocytes display hyperresponsiveness to bacterial lipopolysaccharide and elevated TNF production ex vivo. These findings suggest that NIK governs metabolic rewiring, which is critical for balancing pro- and anti-inflammatory myeloid immune cell function. Overall, our work highlights a previously unrecognized role for NIK as a molecular rheostat that fine-tunes immunometabolism in innate immunity and suggests that metabolic dysfunction may be an important driver of inflammatory diseases caused by aberrant NIK expression or activity. Key PointsO_LINIK-deficient macrophages exhibit impaired mitochondrial oxidative phosphorylation C_LIO_LINIK-deficient mice have more inflammatory myeloid cells in blood and bone marrow C_LIO_LINIK-dependent metabolic rewiring shapes pro- and anti-inflammatory innate immunity C_LI

immunology↗

bioRxiv2021

NF-κB-Inducing Kinase Rewires Metabolic Homeostasis and Promotes Diet-Induced Obesity

BackgroundNF-{kappa}B-inducing kinase (NIK) is a critical regulator of immunity and inflammation and NIK loss-of-function mutations have recently been described in patients with primary immunodeficiency disease. Based on our previous work showing that NIK regulates adaptive metabolic responses in glucose-starved cancer cells, we investigated whether NIK is required for mitochondrial functions in bioenergetic processes and metabolic responses to nutritional stress in NIK knockout (KO) mice, which recapitulate the clinical presentation of NIK PID patients. MethodsWe performed whole body composition analysis of wild type (WT) and NIK KO mice using EchoMRI and DEXA imaging. Seahorse extracellular flux analyses were used to monitor oxidative phosphorylation and glycolysis through oxygen consumption rates (OCR) and extracellular acidification rates (ECAR) in preadipocyte cells and in ex vivo adipose tissue. NIK regulation of systemic metabolic output was measured by indirect calorimetry using TSE Phenomaster metabolic chambers under basal conditions as well as in response to nutritional stress induced by a prolonged high-fat diet (HFD). Finally, we analyzed a role for NIK in adipocyte differentiation, as well as the contributions of canonical and noncanonical NF-{kappa}B signaling to adipose development and metabolic output. ResultsWe observed that in adipose cells, NIK is required for maintaining efficient mitochondrial membrane potential and spare respiratory capacity (SRC), indicators of mitochondrial fitness. NIK KO preadipocytes and ex vivo adipose tissue exhibited diminished SRC, increased proton leak, with compensatory upregulation of glycolysis. Systemically, NIK KO mice exhibited increased glucose utilization, increased energy expenditure, and reduced adiposity, which persisted under the stress of HFD. Finally, while NIK controlled adipocyte differentiation through activation of RelB and the noncanonical NF-{kappa}B pathway, NIK regulation of metabolism in preadipocytes was NF-{kappa}B/RelB-independent. ConclusionOur results demonstrate that NIK is required for metabolic homeostasis both locally, on a cellular and tissue level, as well as systemically, on an organismal level. Collectively, the data suggest that NIK KO cells upregulate glycolytic metabolism as a compensatory response to impaired mitochondrial fitness (diminished SRC) and mitochondrial efficiency (increased proton leak). To meet changes in bioenergetic demands, NIK KO mice undergo metabolic rewiring through increased glucose utilization and glycolysis, which persists under the stress of overnutrition with a HFD. Moreover, while NIK regulation of metabolism is RelB-independent, NIK regulation of adipocyte development requires RelB and activation of the noncanonical NF-{kappa}B pathway. Our findings establish NIK as an important regulator of cellular and systemic metabolic homeostasis, suggesting that metabolic dysfunction may be an important component of primary immunodeficiency diseases arising from loss of NIK function.

physiology↗