Inhibition of PKCε induces primordial germ cell reprogramming into pluripotency by HIF1&2 upregulation and histone acetylation.

Abstract

Historically, primordial germ cells (PGCs) have been a good model to study pluripotency. Despite their low numbers and limited accessibility in the mouse embryo, they can be easily and rapidly reprogrammed at high efficiency with external physicochemical factors and do not require transcription factor transfection. Employing this model to deepen our understanding of cell reprogramming, we specifically aimed to determine the relevance of Ca²⁺ signal transduction pathway components in the reprogramming process. Our results showed that PGC reprogramming requires a normal extracellular [Ca²⁺] range, in contrast to neoplastic or transformed cells, which can continue to proliferate in Ca²⁺-deficient media, differentiating normal reprogramming from neoplastic transformation. Our results also showed that a spike in extracellular [Ca²⁺] of 1-3 mM can directly reprogram PGC. Intracellular manipulation of Ca²⁺ signal transduction pathway components revealed that inhibition of classical Ca²⁺ and diacylglycerol (DAG)-dependent PKCs, or intriguingly, of only the novel DAG-dependent PKC, PKCε, were able to induce reprogramming. PKCε inhibition changed the metabolism of PGCs toward glycolysis, increasing the proportion of inactive mitochondria. This metabolic switch from oxidative phosphorylation to glycolysis is mediated by hypoxia-inducible factors (HIFs), given we found upregulation of both HIF1α and HIF2α in the first 48 hours of culturing. PKCε inhibition did not change the classical pluripotency gene expression of PGCs, Oct4, or Nanog. PKCε inhibition changed the histone acetylation of PGCs, with histones H2B, H3, and H4 becoming acetylated in PKCε-inhibited cultures (markers were H2BacK20, H3acK9, and H4acK5K8, K12, K16), suggesting that reprogramming by PKCε inhibition is mediated by histone acetylation.