ClpP/ClpX deficiency impairs mitochondrial functions and mTORC1 signaling during spermatogenesis and meiosis

Abstract

Caseinolytic protease proteolytic subunit (ClpP) and caseinolytic protease X (ClpX) are mitochondrial matrix peptidases that activate mitochondrial unfolded protein response (mtUPR) to maintain protein homeostasis in the mitochondria. However, the role of ClpP and ClpX in spermatogenesis remains largely unknown. In this study, we demonstrated the importance of ClpP/ClpX for meiosis and spermatogenesis with two conditional knockout (cKO) mouse models. We found that ClpP/ClpX deficiency reduced mitochondrial functions and quantity in spermatocytes, affected energy supply during meiosis and attenuated zygotene-pachytene transformation of the male germ cells. The affected spermatocytes exhibited disorder of chromosome synapsis and cross-over events. Their telomeres failed to attach to the nuclear envelop, which was associated with failure of alpha-tubulin formation in the ClpP/ClpX cKO spermatocytes. The dysregulated spermatocytes finally underwent apoptosis resulting in decreased testicular size and vacuolar structures within the seminiferous tubules. Both transcriptome analysis and m6A-methylation sequencing analysis highlighted dysregulation of metabolic pathways including the mTOR signaling in the isolated spermatocytes. We confirmed over-activation of the mTORC1 pathway with increased expression of phosphorylated S6 and 4EBP after deletion of ClpP/ClpX in spermatocytes. Long-term inhibition of the mTORC1 signaling via rapamycin treatment in vivo partially rescue spermatogenesis in the seminiferous tubules with much less apoptotic germ cells and formation of late stage of meiotic germ cells, such as round spermatids and elongated spermatozoon. The data reveal the novel roles of ClpP and ClpX in regulating meiosis and spermatogenesis.

Engineered Exosomes with ATF5-Modified mRNA Loaded in Injectable Thermogels Alleviate Osteoarthritis by Targeting the Mitochondrial Unfolded Protein Response

“…Studies on the UPR mt and aging have demonstrated that Caseinolytic peptidase P (ClpP) deficiency induced activation of the mTOR pathway, thereby accelerating depletion of ovarian follicular reserves or impairing spermatogenesis. 12,48 Moreover, numerous studies have demonstrated the inhibitory effect of the mTOR pathway on chondrocyte autophagy during OA progression. 13−15 ClpP is a mitochondrial protease that is capable of degrading invalid proteins.…”