Mitochondrial fusion by pharmacological manipulation impedes somatic cell reprogramming to pluripotency: New insight into the role of mitophagy in cell stemness

Alejandro Vazquez-Martin,Sílvia Cufí,Luciano Vellon,Cristina Oliveras-Ferraros,Javier A Menendez,Bruna Corominas-Faja

doi:10.18632/aging.100465

Abstract

Recent studies have suggested a pivotal role for autophagy in stem cell maintenance and differentiation. Reprogramming of somatic cells to induced pluripotent stem cells (iPSCs) has been also suggested to bio-energetically take advantage of mitochondrial autophagy (mitophagy). We have preliminary addressed how mitophagy might play a role in the regulation of induced pluripotency using mdivi-1 (for mitochondrial division inhibitor), a highly efficacious small molecule that selectively inhibits the self-assembly of DRP1, a member of the dynamin family of large GTPases that mediates mitochondrial fission. At mdivi-1 concentrations that rapidly induced the formation of mitochondrial net-like or collapsed perinuclear mitochondrial structures, we observed that the reprogramming efficiency of mouse embryonic fibroblasts transduced with the Yamanaka three-factor cocktail (OCT4, KLF4, and SOX2) is drastically reduced by more than 95%. Treatment of MEFs with mdivi-1 at the early stages of reprogramming before the appearance of iPSC colonies was sufficient to completely inhibit somatic cell reprogramming. Therefore, the observed effects on reprogramming efficiencies were due likely to the inhibition of the process of reprogramming itself and not to an impairment of iPSC colony survival or growth. Moreover, the typical morphology of established iPSC colonies with positive alkaline phosphatase staining was negatively affected by mdivi-1 exposure. In the presence of mdivi-1, the colony morphology of the iPSCs was lost, and they somewhat resembled fibroblasts. The alkaline phosphatase staining was also significantly reduced, a finding that is indicative of differentiation. Our current findings provide new insight into how mitochondrial division is integrated into the reprogramming factors-driven transcriptional network that specifies the unique pluripotency of stem cells.

Highlights

The roles of autophagy in the biology of stem cells have just started to be explored, we are beginning to accumulate strong evidence suggesting that a catabolic process whereby cells generate energy and building blocks by promoting large-scale recycling of cytoplasmic macromolecules and organelles including mitochondria may be essential for the acquisition, maintenance, and exit of stem cell-defining selfrenewing pluripotent states
It is plausible that an mTORregulated increase in mitochondrial fission during the reprogramming of somatic cells to induced pluripotent stem cells (iPSCs) may upregulate mitophagy, which could lead to a significant reduction in both the number and the size of mitochondria to achieve the “mitochondrial phenotype” that is associated with stem cells
An increase in mitochondrial fusion during the reprogramming of somatic cells might downregulate mitophagy, generating giant mitochondria that are associated with cell senescence, which is a pivotal roadblock during the reprogramming process when generating iPSCs

Summary

Introduction

The roles of autophagy in the biology of stem cells have just started to be explored, we are beginning to accumulate strong evidence suggesting that a catabolic process whereby cells generate energy and building blocks by promoting large-scale recycling of cytoplasmic macromolecules and organelles including mitochondria may be essential for the acquisition, maintenance, and exit of stem cell-defining selfrenewing pluripotent states.

Results

Conclusion