Pharmacologic Activation of a Compensatory Integrated Stress Response Kinase Promotes Mitochondrial Remodeling in PERK-deficient Cells

Abstract

The integrated stress response (ISR) is a network of eIF2alpha kinases, comprising PERK, GCN2, HRI, and PKR, that induce translational and transcriptional signaling in response to diverse insults. The PERK ISR kinase regulates mitochondria in response to endoplasmic reticulum (ER) stress. Deficiencies in PERK signaling lead to mitochondrial dysfunction and contribute to the pathogenesis of numerous diseases. We define the potential for pharmacologic activators of other ISR kinases to rescue ISR signaling and promote mitochondrial adaptation in cells lacking PERK. We show that the HRI activator BtdCPU and the GCN2 activator halofuginone activate ISR signaling and restore ER stress sensitivity in Perk-deficient cells. However, these compounds differentially impact mitochondria. BtdCPU induces mitochondrial depolarization, leading to mitochondrial fragmentation and ISR activation through the OMA1-DELE1-HRI signaling axis. In contrast, halofuginone promotes mitochondrial elongation and altered mitochondrial respiration, mimicking the regulation induced by PERK. This shows halofuginone can compensate for deficiencies in PERK activity and promote adaptive mitochondrial remodeling, highlighting the potential for pharmacologic ISR activation to mitigate mitochondrial dysfunction and motivating the pursuit of highly-selective ISR activators.

Mapping stress-responsive signaling pathways induced by mitochondrial proteostasis perturbations

“…Our identification of the ISR as the predominant stress-responsive signaling pathway activated by CRISPRi-mediated mitochondrial proteotoxic stress underscores a unique opportunity to target the ISR to correct pathologic mitochondrial dysfunction in etiologically diverse diseases. For example, recent work showed that pharmacologic activation of the ISR kinase GCN2 reduced mitochondrial fragmentation and respiratory chain dysfunction in cells deficient in the ISR kinase PERK ( Perea et al. , 2023a ) – a condition linked to many neurodegenerative diseases including Alzheimer’s disease and Progressive Supranuclear Palsy ( Yuan et al.…”

“…Further, ISR-dependent translational attenuation regulates mitochondrial protein import through the degradation of the core import subunit TIM17A ( Rainbolt et al. , 2013 ; Perea et al. , 2023a ).…”