P53 is required for nuclear but not mitochondrial DNA damage-induced degeneration

Matthew J Geden,Mohanish Deshmukh,Selena E Romero

doi:10.1038/s41419-020-03373-1

Matthew J Geden, Mohanish Deshmukh + Show 1 more

Open Access

https://doi.org/10.1038/s41419-020-03373-1

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Abstract

While the consequences of nuclear DNA damage have been well studied, the exact consequences of acute and selective mitochondrial DNA (mtDNA) damage are less understood. DNA damaging chemotherapeutic drugs are known to activate p53-dependent apoptosis in response to sustained nuclear DNA damage. While it is recognized that whole-cell exposure to these drugs also damages mtDNA, the specific contribution of mtDNA damage to cellular degeneration is less clear. To examine this, we induced selective mtDNA damage in neuronal axons using microfluidic chambers that allow for the spatial and fluidic isolation of neuronal cell bodies (containing nucleus and mitochondria) from the axons (containing mitochondria). Exposure of the DNA damaging drug cisplatin selectively to only the axons induced mtDNA damage in axonal mitochondria, without nuclear damage. We found that this resulted in the selective degeneration of only the targeted axons that were exposed to DNA damage, where ROS was induced but mitochondria were not permeabilized. mtDNA damage-induced axon degeneration was not mediated by any of the three known axon degeneration pathways: apoptosis, axon pruning, and Wallerian degeneration, as Bax-deficiency, or Casp3-deficiency, or Sarm1-deficiency failed to protect the degenerating axons. Strikingly, p53, which is essential for degeneration after nuclear DNA damage, was also not required for degeneration induced with mtDNA damage. This was most evident when the p53-deficient neurons were globally exposed to cisplatin. While the cell bodies of p53-deficient neurons were protected from degeneration in this context, the axons farthest from the cell bodies still underwent degeneration. These results highlight how whole cell exposure to DNA damage activates two pathways of degeneration; a faster, p53-dependent apoptotic degeneration that is triggered in the cell bodies with nuclear DNA damage, and a slower, p53-independent degeneration that is induced with mtDNA damage.

Highlights

Introduction The maintenance of cellularDNA integrity and the elimination of cells that have sustained excessive DNA damage is fundamentally important for all organisms
As we found axon degeneration induced by cisplatin exposure to be a p53-independent process, we sought to identify the degenerative pathway activated with selective mitochondrial DNA (mtDNA) damage
In this study we highlight the differential importance for p53 in governing the degenerative response to sustained nuclear versus mitochondrial DNA damage

Summary

Introduction

DNA integrity and the elimination of cells that have sustained excessive DNA damage is fundamentally important for all organisms. While mitochondrial DNA (mtDNA) is several orders of magnitude smaller than the nuclear genome[1], maintenance of mtDNA integrity is crucial as mutations in mtDNA have been shown to be important in a number of diseases including cancer, neurodegenerative diseases, and aging[2,3]. Chemotherapeutic drugs that induce DNA damage are frontline treatments for cancer therapy[4]. These DNAdamaging events engage a number of downstream pathways depending on the degree of damage. While low levels of DNA damage can be repaired, induce cell cycle arrest, senescence, or differentiation, excessive damage can lead to cell death via apoptosis[5]. It has become increasingly evident that exposure of cells to genotoxic drugs affects not just nuclear DNA and mitochondrial DNA8

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