Metabolic rescue ameliorates mitochondrial encephalo‐cardiomyopathy in murine and human iPSC models of Leigh syndrome

Abstract

Background Mice with deletion of complex I subunit Ndufs4 develop mitochondrial encephalomyopathy resembling Leigh syndrome (LS). The metabolic derangement and underlying mechanisms of cardio‐encephalomyopathy in LS remains incompletely understood. Methods We performed echocardiography, electrophysiology, confocal microscopy, metabolic and molecular/morphometric analysis of the mice lacking Ndufs4. HEK293 cells, human iPS cells‐derived cardiomyocytes and neurons were used to determine the mechanistic role of mitochondrial complex I deficiency. Results LS mice develop severe cardiac bradyarrhythmia and diastolic dysfunction. Human‐induced pluripotent stem cell‐derived cardiomyocytes (iPS‐CMs) with Ndufs4 deletion recapitulate LS cardiomyopathy. Mechanistically, we demonstrate a direct link between complex I deficiency, decreased intracellular (nicotinamide adenine dinucleotide) NAD + /NADH and bradyarrhythmia, mediated by hyperacetylation of the cardiac sodium channel Na V 1.5, particularly at K1479 site. Neuronal apoptosis in the cerebellar and midbrain regions in LS mice was associated with hyperacetylation of p53 and activation of microglia. Targeted metabolomics revealed increases in several amino acids and citric acid cycle intermediates, likely due to impairment of NAD + ‐dependent dehydrogenases, and a substantial decrease in reduced Glutathione (GSH). Metabolic rescue by nicotinamide riboside (NR) supplementation increased intracellular NAD + / NADH, restored metabolic derangement, reversed protein hyperacetylation through NAD + ‐dependent Sirtuin deacetylase, and ameliorated cardiomyopathic phenotypes, concomitant with improvement of Na V 1.5 current and SERCA2a function measured by Ca2 + ‐transients. NR also attenuated neuronal apoptosis and microglial activation in the LS brain and human iPS‐derived neurons with Ndufs4 deletion. Conclusions Our study reveals direct mechanistic explanations of the observed cardiac bradyarrhythmia, diastolic dysfunction and neuronal apoptosis in mouse and human induced pluripotent stem cells (iPSC) models of LS.

ATP and NAD+ Deficiency in Parkinson’s Disease

“…The NAD + /NADH ratio is essential to maintaining redox balance of the cell, and reduced concentrations of NAD are linked to poor metabolic health in aging and chronic diseases [ 21 , 22 ]. Elevating NAD levels by targeted supplementation has improved health and reversed pathology in animal models of disease [ 23 , 24 ], and NAD enhancing supplements are currently being tested in clinical trials for multiple human conditions [ 25 , 26 , 27 ]. The therapeutic use of NAD+ precursors, such as nicotinamide riboside (NR), as a therapeutic target to compensate for deficits in complex I, is particularly appealing in PD [ 28 ].…”

Activated microglia and neuroinflammation as a pathogenic mechanism in Leigh syndrome

“…To examine the role of microglia in LS encephalopathy, we used LS mouse model with Ndufs4 −/− , which developed multiple brain lesions, particularly in the brainstem and cerebellum, associated with increase in microglia (Quintana et al, 2010 ; Yoon et al, 2022 ). We showed that partial ablation of microglia by Pexidartinib may confer protective effect and extend lifespan of Ndufs4 −/− mice, but only when it was administered approximately at the onset of neurological symptoms during which activated microglia has been documented (Quintana et al, 2010 ; Aguilar et al, 2022 ; Yoon et al, 2022 ) (late Pexi, Figure 3 ).…”

“…To examine the role of microglia in LS encephalopathy, we used LS mouse model with Ndufs4 −/− , which developed multiple brain lesions, particularly in the brainstem and cerebellum, associated with increase in microglia (Quintana et al, 2010 ; Yoon et al, 2022 ). We showed that partial ablation of microglia by Pexidartinib may confer protective effect and extend lifespan of Ndufs4 −/− mice, but only when it was administered approximately at the onset of neurological symptoms during which activated microglia has been documented (Quintana et al, 2010 ; Aguilar et al, 2022 ; Yoon et al, 2022 ) (late Pexi, Figure 3 ). A plausible explanation for the detrimental effects of early Pexi in depleting microglia is that microglia play critical physiological roles in phagocytosis of cellular debris, secretion of signaling molecules (e.g., neurotrophins) and essential homeostasis during CNS development, maturation and in diseased state (Anderson and Vetter, 2019 ).…”

“…Another limitation is the inadequate maturity of iPSC-derived neurons, since in vitro maturation will not match the in-utero growth and development, including the degree of mitochondrial maturation (Dai et al, 2017 ). However, because LS is a disease of very early onset (the age of infant to toddler), iPSC approach has proven to be valuable to model LS (Inak et al, 2021 ; Yoon et al, 2022 ). The recent development of iPSC-derived brain organoids has enabled complex modeling of human diseases, such as those involving interactions of multiple cell types, as we reported here to show increased pro-inflammatory pathways in LS brain organoid.…”

How to mitigate neurological and cardiac decompensation in Leigh syndrome: Can nicotinamide riboside be an answer?

“…The mechanisms underlying its pathogenesis are not fully understood and no therapies are approved for the treatment of patients with LS. In a new study, Yoon and colleagues 1 shed light on the pathophysiological mechanisms of cardio‐encephalomyopathy in LS and demonstrates that nicotiname riboside (NR) provides significant amelioration in disease models of LS (Figure 1).…”