bims-smemid 2025-02-02 papers

Biomolecules. 2024 Dec 31. pii: 38. [Epub ahead of print]15(1):

NADH Reductive Stress and Its Correlation with Disease Severity in Leigh Syndrome: A Pilot Study Using Patient Fibroblasts and a Mouse Model.

Tamaki Ishima, Natsuka Kimura, Mizuki Kobayashi, Chika Watanabe, Eriko F Jimbo, Ryosuke Kobayashi, Takuro Horii, Izuho Hatada, Kei Murayama, Akira Ohtake, Ryozo Nagai, Hitoshi Osaka, Kenichi Aizawa.

Nicotinamide adenine dinucleotide (NAD) is a critical cofactor in mitochondrial energy production. The NADH/NAD+ ratio, reflecting the balance between NADH (reduced) and NAD+ (oxidized), is a key marker for the severity of mitochondrial diseases. We recently developed a streamlined LC-MS/MS method for the precise measurement of NADH and NAD+. Utilizing this technique, we quantified NADH and NAD+ levels in fibroblasts derived from pediatric patients and in a Leigh syndrome mouse model in which mitochondrial respiratory chain complex I subunit Ndufs4 is knocked out (KO). In patient-derived fibroblasts, NAD+ levels did not differ significantly from those of healthy controls (p = 0.79); however, NADH levels were significantly elevated (p = 0.04), indicating increased NADH reductive stress. This increase, observed despite comparable total NAD(H) levels between the groups, was attributed to elevated NADH levels. Similarly, in the mouse model, NADH levels were significantly increased in the KO group (p = 0.002), further suggesting that NADH elevation drives reductive stress. This precise method for NADH measurement is expected to outperform conventional assays, such as those for lactate, providing a simpler and more reliable means of assessing disease progression.

Keywords: LC-MS/MS; Leigh syndrome; NADH; Ndufs4-KO mice; mitochondrial diseases; reductive stress

DOI: https://doi.org/10.3390/biom15010038

Cell Mol Biol Lett. 2025 Jan 09. 30(1): 3

Failure to repair damaged NAD(P)H blocks de novo serine synthesis in human cells.

Adhish S Walvekar, Marc Warmoes, Dean Cheung, Tim Sikora, Najmesadat Seyedkatouli, Gemma Gomez-Giro, Sebastian Perrone, Lisa Dengler, François Unger, Bruno F R Santos, Floriane Gavotto, Xiangyi Dong, Julia Becker-Kettern, Yong-Jun Kwon, Christian Jäger, Jens C Schwamborn, Nicole J Van Bergen, John Christodoulou, Carole L Linster.

BACKGROUND: Metabolism is error prone. For instance, the reduced forms of the central metabolic cofactors nicotinamide adenine dinucleotide (NADH) and nicotinamide adenine dinucleotide phosphate (NADPH), can be converted into redox-inactive products, NADHX and NADPHX, through enzymatically catalyzed or spontaneous hydration. The metabolite repair enzymes NAXD and NAXE convert these damaged compounds back to the functional NAD(P)H cofactors. Pathogenic loss-of-function variants in NAXE and NAXD lead to development of the neurometabolic disorders progressive, early-onset encephalopathy with brain edema and/or leukoencephalopathy (PEBEL)1 and PEBEL2, respectively.
METHODS: To gain insights into the molecular disease mechanisms, we investigated the metabolic impact of NAXD deficiency in human cell models. Control and NAXD-deficient cells were cultivated under different conditions, followed by cell viability and mitochondrial function assays as well as metabolomic analyses without or with stable isotope labeling. Enzymatic assays with purified recombinant proteins were performed to confirm molecular mechanisms suggested by the cell culture experiments.
RESULTS: HAP1 NAXD knockout (NAXDko) cells showed growth impairment specifically in a basal medium containing galactose instead of glucose. Surprisingly, the galactose-grown NAXDko cells displayed only subtle signs of mitochondrial impairment, whereas metabolomic analyses revealed a strong inhibition of the cytosolic, de novo serine synthesis pathway in those cells as well as in NAXD patient-derived fibroblasts. We identified inhibition of 3-phosphoglycerate dehydrogenase as the root cause for this metabolic perturbation. The NAD precursor nicotinamide riboside (NR) and inosine exerted beneficial effects on HAP1 cell viability under galactose stress, with more pronounced effects in NAXDko cells. Metabolomic profiling in supplemented cells indicated that NR and inosine act via different mechanisms that at least partially involve the serine synthesis pathway.
CONCLUSIONS: Taken together, our study identifies a metabolic vulnerability in NAXD-deficient cells that can be targeted by small molecules such as NR or inosine, opening perspectives in the search for mechanism-based therapeutic interventions in PEBEL disorders.

Keywords: 3-Phosphoglycerate dehydrogenase; Inborn errors of metabolism; Inosine; Metabolite damage and repair; NAD(P)H hydration; NAXD; Nicotinamide riboside; Serine biosynthesis

DOI: https://doi.org/10.1186/s11658-024-00681-8

Life Metab. 2025 Feb;4(1): loae040

Glucose-6-phosphate dehydrogenase regulates mitophagy by maintaining PINK1 stability.

Yik-Lam Cho, Hayden Weng Siong Tan, Jicheng Yang, Basil Zheng Mian Kuah, Nicole Si Ying Lim, Naiyang Fu, Boon-Huat Bay, Shuo-Chien Ling, Han-Ming Shen.

Glucose-6-phosphate dehydrogenase (G6PD) is the rate-limiting enzyme in the pentose phosphate pathway (PPP) in glycolysis. Glucose metabolism is closely implicated in the regulation of mitophagy, a selective form of autophagy for the degradation of damaged mitochondria. The PPP and its key enzymes such as G6PD possess important metabolic functions, including biosynthesis and maintenance of intracellular redox balance, while their implication in mitophagy is largely unknown. Here, via a whole-genome CRISPR-Cas9 screening, we identified that G6PD regulates PINK1 (phosphatase and tensin homolog [PTEN]-induced kinase 1)-Parkin-mediated mitophagy. The function of G6PD in mitophagy was verified via multiple approaches. G6PD deletion significantly inhibited mitophagy, which can be rescued by G6PD reconstitution. Intriguingly, while the catalytic activity of G6PD is required, the known PPP functions per se are not involved in mitophagy regulation. Importantly, we found a portion of G6PD localized at mitochondria where it interacts with PINK1. G6PD deletion resulted in an impairment in PINK1 stabilization and subsequent inhibition of ubiquitin phosphorylation, a key starting point of mitophagy. Finally, we found that G6PD deletion resulted in lower cell viability upon mitochondrial depolarization, indicating the physiological function of G6PD-mediated mitophagy in response to mitochondrial stress. In summary, our study reveals a novel role of G6PD as a key positive regulator in mitophagy, which bridges several important cellular processes, namely glucose metabolism, redox homeostasis, and mitochondrial quality control.

Keywords: G6PD; NADPH; PINK1; PPP; ROS; mitophagy

DOI: https://doi.org/10.1093/lifemeta/loae040