Protein Phosphatase Magnesium-Dependent 1H Exacerbates Intestinal Ischemia/Reperfusion Injury by Promoting FUN14 Domain-Containing 1-Dependent Mitophagy.

INTRODUCTION Intestinal ischemia/reperfusion (I/R) injury causes severe mucosal damage via mitochondrial dysfunction. While mitophagy regulates mitochondrial quality, its specific modulation by protein phosphatase magnesium-dependent 1H (PPM1H) remains unclear. We investigated PPM1H's role and its mechanism involving FUN14 domain-containing 1 (FUNDC1)-mediated mitophagy.

Methods

Intestinal I/R injury was modeled in C57BL/6 mice by occluding the superior mesenteric artery for 60 min followed by 120 min of reperfusion. In vitro, mouse intestinal mucosa epithelial (MIME) cells were subjected to oxygen-glucose deprivation/reoxygenation (OGD/R). In MIME cells, PPM1H expression was knocked down using specific siRNA prior to OGD/R challenge. Histological evaluation, cell viability, diamine oxidase (DAO) activity, mitochondrial autophagosome formation, apoptotic index, and the expression levels of key proteins were assessed.

Results

Both in vivo and in vitro models showed that PPM1H and total FUNDC1 were upregulated, while the relative phosphorylation level of FUNDC1 at Ser13 (p-FUNDC1-Ser13) was downregulated following I/R or OGD/R injury. Concurrently, mitophagy was activated, as evidenced by an increased LC3-II/LC3-I ratio and decreased p62 levels. These changes were accompanied by significant intestinal damage, elevated DAO levels, and increased apoptosis. Conversely, knockdown of PPM1H in MIME cells reversed these effects: it increased p-FUNDC1-Ser13/total FUNDC1 ratio, suppressed mitophagy, improved cell survival, reduced DAO release, and attenuated apoptosis.

Conclusions

PPM1H was upregulated during intestinal I/R injury and might exacerbate damage by regulating excessive mitophagy through mediating the dephosphorylation of FUNDC1 at Ser13, which subsequently regulates apoptosis. Thus, our findings revealed PPM1H as a closely associated regulator in intestinal I/R injury.