Pluripotent stem cells hold great promise in regenerative medicine and developmental biology studies. Mitochondrial metabolites, including tricarboxylic acid (TCA) cycle intermediates, have been reported to play critical roles in pluripotency. Here we show that TCA cycle enzymes including Pdha1, Pcb, Aco2, Cs, Idh3a, Ogdh, Sdha and Mdh2 are translocated to the nucleus during somatic cell reprogramming, primed-to-naive transition and totipotency acquisition. The nuclear-localized TCA cycle enzymes Pdha1, Pcb, Aco2, Cs, Idh3a promote somatic cell reprogramming and primed-to-naive transition. In addition, nuclear-localized TCA cycle enzymes, particularly nuclear-targeted Pdha1, facilitate the 2-cell program in pluripotent stem cells. Mechanistically, nuclear Pdha1 increases the acetyl-CoA and metabolite pool in the nucleus, leading to chromatin remodeling at pluripotency genes by enhancing histone H3 acetylation. Our results reveal an important role of mitochondrial TCA cycle enzymes in the epigenetic regulation of pluripotency that constitutes a mitochondria-to-nucleus retrograde signaling mode in different states of pluripotent acquisition.

Mammals' aging is correlated with the accumulation of somatic heteroplasmic mitochondrial DNA (mtDNA) mutations. Whether and how aging accumulated mtDNA mutations modulate fertility remains unknown. Here, we analyzed oocyte quality of young (≤30 years old) and elder (≥38 years old) female patients and show the elder group had lower blastocyst formation rate and more mtDNA point mutations in oocytes. To test the causal role of mtDNA point mutations on infertility, we used polymerase gamma (POLG) mutator mice. We show that mtDNA mutation levels inversely correlate with fertility, interestingly mainly affecting not male but female fertility. mtDNA mutations decrease female mice's fertility by reducing ovarian primordial and mature follicles. Mechanistically, accumulation of mtDNA mutations decreases fertility by impairing oocyte's NADH/NAD⁺ redox state, which could be rescued by nicotinamide mononucleotide treatment. For the first time, we answer the fundamental question of the causal effect of age‐accumulated mtDNA mutations on fertility and its sex dependence, and show its distinct metabolic controlling mechanism.

Valproic acid (VPA) is widely used to treat epilepsy, migraine, chronic headache, bipolar disorder, and as adjuvant chemotherapy, but potentially causes idiosyncratic liver injury. Alpers‐Huttenlocher syndrome (AHS), a neurometabolic disorder caused by mutations in mitochondrial DNA polymerase gamma (POLG), is associated with an increased risk of developing fatal VPA hepatotoxicity. However, the mechanistic link of this clinical mystery remains unknown. Here, fibroblasts from 2 AHS patients were reprogrammed to induced pluripotent stem cells (iPSCs) and then differentiated to hepatocyte‐like cells (AHS iPSCs‐Hep). Both AHS iPSCs‐Hep are more sensitive to VPA‐induced mitochondrial‐dependent apoptosis than controls, showing more activated caspase‐9 and cytochrome c release. Strikingly, levels of both soluble and oligomeric optic atrophy 1, which together keep cristae junctions tight, are reduced in AHS iPSCs‐Hep. Furthermore, POLG mutation cells show reduced POLG expression, mitochondrial DNA (mtDNA) amount, mitochondrial adenosine triphosphate production, as well as abnormal mitochondrial ultrastructure after differentiation to hepatocyte‐like cells. Superoxide flashes, spontaneous bursts of superoxide generation, caused by opening of the mitochondrial permeability transition pore (mPTP), occur more frequently in AHS iPSCs‐Hep. Moreover, the mPTP inhibitor, cyclosporine A, rescues VPA‐induced apoptotic sensitivity in AHS iPSCs‐Hep. This result suggests that targeting mPTP opening could be an effective method to prevent hepatotoxicity by VPA in AHS patients. In addition, carnitine or N‐acetylcysteine, which has been used in the treatment of VPA‐induced hepatotoxicity, is able to rescue VPA‐induced apoptotic sensitivity in AHS iPSCs‐Hep. Conclusion: AHS iPSCs‐Hep are more sensitive to the VPA‐induced mitochondrial‐dependent apoptotic pathway, and this effect is mediated by mPTP opening. Toxicity models in genetic diseases using iPSCs enable the evaluation of drugs for therapeutic targets. (Hepatology 2015;61:1730‐1739)