Skeletal progenitors preserve proliferation and self-renewal upon inhibition of mitochondrial respiration by rerouting the TCA cycle

A functional electron transport chain (ETC) is crucial for maintaining bioenergetic and biosynthetic processes. Accordingly, inhibition of the ETC decreases proliferation in cancer cells. Intriguingly, ETC blockade does not seem to impair stem cell proliferation, but it remains unknown how stem cells metabolically adapt. In this study, we show that pharmacological inhibition of complex III of the ETC in skeletal stem and progenitor cells induces glycolysis side pathways and reroutes the tricarboxylic acid (TCA) cycle to regenerate NAD+ and preserve cell proliferation. These metabolic changes also culminate in increased succinate and 2-hydroxyglutarate levels that inhibit Ten-eleven translocation (TET) DNA demethylase activity, thereby preserving self-renewal and multilineage potential. Mechanistically, mitochondrial malate dehydrogenase and reverse succinate dehydrogenase activity proved essential for the metabolic rewiring in response to ETC inhibition. Together, these data show that the high metabolic plasticity of skeletal stem and progenitor cells allow them to bypass ETC blockade and preserve their self-renewal.

功能性电子传递链（electron transport chain, ETC）是维持细胞生物能代谢与生物合成过程的关键要素。因此，抑制电子传递链会削弱癌细胞的增殖活性。值得注意的是，电子传递链阻断似乎并不会损伤干细胞的增殖能力，但目前学界仍未明确干细胞实现代谢适应性调控的具体机制。本研究证实，在骨骼干细胞与祖细胞中，对电子传递链复合物III的药理学抑制可激活糖酵解旁路通路，并重新定向三羧酸（tricarboxylic acid, TCA）循环以再生烟酰胺腺嘌呤二核苷酸（nicotinamide adenine dinucleotide, NAD+），进而维持细胞增殖活性。上述代谢变化最终会导致琥珀酸与2-羟基戊二酸（2-hydroxyglutarate）水平升高，二者可抑制十-十一易位（Ten-eleven translocation, TET）DNA去甲基化酶的活性，从而维持干细胞的自我更新能力与多系分化潜能。机制研究表明，线粒体苹果酸脱氢酶与反向琥珀酸脱氢酶的活性，是响应电子传递链抑制的代谢重编程过程所必需的关键环节。综上，本研究数据表明，骨骼干细胞与祖细胞具备高度的代谢可塑性，使其能够规避电子传递链阻断带来的影响，维持自身的自我更新能力。