SUMMARY Regeneration capacity declines with age, but why juvenile organisms show enhanced tissue repair remains unexplained. Lin28a, a highly-conserved RNA binding protein expressed during embryogenesis, plays roles in development, pluripotency and metabolism. To determine if Lin28a might influence tissue repair in adults, we engineered the reactivation of Lin28a expression in several models of tissue injury. Lin28a reactivation improved hair regrowth by promoting anagen in hair follicles, and accelerated regrowth of cartilage, bone and mesenchyme after ear and digit injuries. Lin28a inhibits let-7 microRNA biogenesis; however let-7 repression was necessary but insufficient to enhance repair. Lin28a bound to and enhanced the translation of mRNAs for several metabolic enzymes, thereby increasing glycolysis and oxidative phosphorylation (OxPhos). Lin28a-mediated enhancement of tissue repair was negated by OxPhos inhibition, whereas a pharmacologically-induced increase in OxPhos enhanced repair. Thus, Lin28a enhances tissue repair in some adult tissues by reprogramming cellular bioenergetics.

The RNA-binding proteins LIN28A and LIN28B play critical roles in embryonic development, tumorigenesis, and pluripotency, but their exact functions are poorly understood. Here, we show that, like LIN28A, LIN28B can function effectively with NANOG, OCT4, and SOX2 in reprogramming to pluripotency and that reactivation of both endogenous LIN28A and LIN28B loci are required for maximal reprogramming efficiency. In human fibroblasts, LIN28B is activated early during reprogramming, while LIN28A is activated later during the transition to bona fide induced pluripotent stem cells (iPSCs). In murine cells, LIN28A and LIN28B facilitate conversion from naive to primed pluripotency. Proteomic and metabolomic analysis highlighted roles for LIN28 in maintaining the low mitochondrial function associated with primed pluripotency and in regulating one-carbon metabolism, nucleotide metabolism, and histone methylation. LIN28 binds to mRNAs of proteins important for oxidative phosphorylation and modulates protein abundance. Thus, LIN28A and LIN28B play cooperative roles in regulating reprogramming, naive/primed pluripotency, and stem cell metabolism.

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