Regulation of the urea cycle by CPS1 O-GlcNAcylation in response to dietary restriction and aging

Glycosylation in aging and neurodegenerative diseases

Aging, a complex biological process, involves the progressive decline of physiological functions across various systems, leading to increased susceptibility to neurodegenerative diseases. In society, demographic aging imposes significant economic and social burdens due to these conditions. This review specifically examines the association of protein glycosylation with aging and neurodegenerative diseases. Glycosylation, a critical post-translational modification, influences numerous aspects of protein function that are pivotal in aging and the pathophysiology of diseases such as Alzheimer's disease, Parkinson's disease, and other neurodegenerative conditions. We highlight the alterations in glycosylation patterns observed during aging, their implications in the onset and progression of neurodegenerative diseases, and the potential of glycosylation profiles as biomarkers for early detection, prognosis, and monitoring of these age-associated conditions, and delve into the mechanisms of glycosylation. Furthermore, this review explores their role in regulating protein function and mediating critical biological interactions in these diseases. By examining the changes in glycosylation profiles associated with each part, this review underscores the potential of glycosylation research as a tool to enhance our understanding of aging and its related diseases.

IDH2, a novel target of OGT, facilitates glucose uptake and cellular bioenergy production via NF-κB signaling to promote colorectal cancer progression

BACKGROUND

Although isocitrate dehydrogenase 2 (IDH2) mutations have been the hotspots in recent anticancer studies, the impact of wild-type IDH2 on cancer cell growth and metabolic alterations is still elusive.

METHODS

IDH2 expression in CRC tissues was evaluated by immunohistochemistry, and the correlation between the expression level and the patient's survival rate was analyzed. Cell functional assays included CCK8 and colony formation for cell proliferation in vitro and ectopic xenograft as in vivo experimental model for tumor progression. A targeted metabolomic procedure was performed by liquid chromatography/tandem mass spectrometry to profile the metabolites from glycolysis and tricarboxylic acid (TCA) cycle. Mitochondrial function was assessed by measuring cellular oxygen consumption (OCR) and mitochondrial membrane potential (ΔΨ). Confocal microscope analysis and Western blotting were applied to detect the expression of GLUT1 and NF-κB signaling. O-GlcNAcylation and the interaction of IDH2 with OGT were confirmed by co-immunoprecipitation, followed by Western blotting analysis.

RESULTS

IDH2 protein was highly expressed in CRC tissues, and correlated with poor survival of CRC patients. Wild-type IDH2 promoted CRC cell growth in vitro and tumor progression in xenograft mice. Overexpression of wild-type IDH2 significantly increased glycolysis and TCA cycle metabolites, the ratios of NADH/NAD⁺ and ATP/ADP, OCR and mitochondrial membrane potential (ΔΨ) in CRC cells. Furthermore, α-KG activated NF-κB signaling to promote glucose uptake by upregulating GLUT1. Interesting, O-GlcNAcylation enhanced the protein half-time of IDH2 by inhibiting ubiquitin-mediated proteasome degradation. The O-GlcNAc transferase (OGT)-IDH2 axis promoted CRC progression.

CONCLUSION

Wild-type IDH2 reprogrammed glucose metabolism and bioenergetic production via the NF-κB signaling pathway to promote CRC development and progression. O-GlcNAcylation of IDH2 elevated the stability of IDH2 protein. And the axis of OGT-IDH2 played an essential promotive role in tumor progression, suggesting a novel potential therapeutic strategy in CRC treatment.

Emerging Role of Protein O-GlcNAcylation in Liver Metabolism: Implications for Diabetes and NAFLD

O-linked b-N-acetyl-glucosaminylation (O-GlcNAcylation) is one of the most common post-translational modifications of proteins, and is established by modifying the serine or threonine residues of nuclear, cytoplasmic, and mitochondrial proteins. O-GlcNAc signaling is considered a critical nutrient sensor, and affects numerous proteins involved in cellular metabolic processes. O-GlcNAcylation modulates protein functions in different patterns, including protein stabilization, enzymatic activity, transcriptional activity, and protein interactions. Disrupted O-GlcNAcylation is associated with an abnormal metabolic state, and may result in metabolic disorders. As the liver is the center of nutrient metabolism, this review provides a brief description of the features of the O-GlcNAc signaling pathway, and summarizes the regulatory functions and underlying molecular mechanisms of O-GlcNAcylation in liver metabolism. Finally, this review highlights the role of O-GlcNAcylation in liver-associated diseases, such as diabetes and nonalcoholic fatty liver disease (NAFLD). We hope this review not only benefits the understanding of O-GlcNAc biology, but also provides new insights for treatments against liver-associated metabolic disorders.

Protein O-GlcNAcylation in Metabolic Modulation of Skeletal Muscle: A Bright but Long Way to Go

O-GlcNAcylation is an atypical, dynamic and reversible O-glycosylation that is critical and abundant in metazoan. O-GlcNAcylation coordinates and receives various signaling inputs such as nutrients and stresses, thus spatiotemporally regulating the activity, stability, localization and interaction of target proteins to participate in cellular physiological functions. Our review discusses in depth the involvement of O-GlcNAcylation in the precise regulation of skeletal muscle metabolism, such as glucose homeostasis, insulin sensitivity, tricarboxylic acid cycle and mitochondrial biogenesis. The complex interaction and precise modulation of O-GlcNAcylation in these nutritional pathways of skeletal muscle also provide emerging mechanical information on how nutrients affect health, exercise and disease. Meanwhile, we explored the potential role of O-GlcNAcylation in skeletal muscle pathology and focused on its benefits in maintaining proteostasis under atrophy. In general, these understandings of O-GlcNAcylation are conducive to providing new insights into skeletal muscle (patho) physiology.

O-GlcNAcylation enhances CPS1 catalytic efficiency for ammonia and promotes ureagenesis

Life-threatening hyperammonemia occurs in both inherited and acquired liver diseases affecting ureagenesis, the main pathway for detoxification of neurotoxic ammonia in mammals. Protein O-GlcNAcylation is a reversible and nutrient-sensitive post-translational modification using as substrate UDP-GlcNAc, the end-product of hexosamine biosynthesis pathway. Here we show that increased liver UDP-GlcNAc during hyperammonemia increases protein O-GlcNAcylation and enhances ureagenesis. Mechanistically, O-GlcNAcylation on specific threonine residues increased the catalytic efficiency for ammonia of carbamoyl phosphate synthetase 1 (CPS1), the rate-limiting enzyme in ureagenesis. Pharmacological inhibition of O-GlcNAcase, the enzyme removing O-GlcNAc from proteins, resulted in clinically relevant reductions of systemic ammonia in both genetic (hypomorphic mouse model of propionic acidemia) and acquired (thioacetamide-induced acute liver failure) mouse models of liver diseases. In conclusion, by fine-tuned control of ammonia entry into ureagenesis, hepatic O-GlcNAcylation of CPS1 increases ammonia detoxification and is a novel target for therapy of hyperammonemia in both genetic and acquired diseases.

Aberrant methylmalonylation underlies methylmalonic acidemia and is attenuated by an engineered sirtuin

Organic acidemias such as methylmalonic acidemia (MMA) are a group of inborn errors of metabolism that typically arise from defects in the catabolism of amino and fatty acids. Accretion of acyl-CoA species is postulated to underlie disease pathophysiology, but the mechanism(s) remain unknown. Here, we surveyed hepatic explants from patients with MMA and unaffected donors, in parallel with samples from various mouse models of methylmalonyl-CoA mutase deficiency. We found a widespread posttranslational modification, methylmalonylation, that inhibited enzymes in the urea cycle and glycine cleavage pathway in MMA. Biochemical studies and mouse genetics established that sirtuin 5 (SIRT5) controlled the metabolism of MMA-related posttranslational modifications. SIRT5 was engineered to resist acylation-driven inhibition via lysine to arginine mutagenesis. The modified SIRT5 was used to create an adeno-associated viral 8 (AAV8) vector and systemically delivered to mutant and control mice. Gene therapy ameliorated hyperammonemia and reduced global methylmalonylation in the MMA mice.