Uma Naresh, N. | bioRxiv Science

bioRxiv2022

ATFS-1 regulates peroxisome assembly genes and protects both mitochondria and peroxisomes during peroxin perturbations

Peroxisome biogenesis disorders lead to a myriad of clinical manifestations, among which is the dysfunction of the mitochondria. Mitochondria dysfunction is typically sensed by the UPRmt, a broad protective transcriptional response governed by the transcription factor ATFS-1. Here, we investigated the role of the UPRmt during peroxisomal stress. We show that mutations or knockdown of peroxins, the genes required for peroxisome assembly, lead to mitochondria dysfunction and the induction of the UPRmt in C.elegans. The UPRmt induced the transcription of the mitochondrial outer membrane translocase mspn-1 (ATAD-1), that in turn alleviated mitochondrial stress most likely by extracting mislocalized proteins. Importantly, ATFS-1 regulated the transcription of peroxins and the peroxisomal transporter pmp-4. A prx-5 loss of function strain induced a retrograde response that resulted in the transcriptional induction of peroxins, peroxisomal transporters, chaperons and proteases. And was dependent on ATFS-1 and on the peroxisome proliferator activator receptor alpha, NHR-49. Knockout of atfs-1 during peroxisomal stress resulted in severe developmental delays, import defects to peroxisomes and the appearance of large peroxisomal structures. We propose that ATFS-1 regulates the biogenesis of peroxisomes and protects the organism by alleviating the stress of both peroxisomes and mitochondria during peroxisomal stress.

developmental biology↗

bioRxiv2020

UPRmt scales mitochondrial network expansion with protein synthesis via mitochondrial import

As organisms develop, individual cells generate mitochondria to fulfill physiologic requirements. However, it remains unknown how mitochondrial network expansion is scaled to cell growth and impacted by environmental cues. The mitochondrial unfolded protein response (UPRmt) is a signaling pathway mediated by the transcription factor ATFS-1 which harbors a mitochondrial targeting sequence (MTS)1. Here, we demonstrate that ATFS-1 mediates an adaptable mitochondrial expansion program that is active throughout normal development. Developmental mitochondrial network expansion required the relatively inefficient MTS2 in ATFS-1, which allowed the transcription factor to be responsive to parameters that impact protein import capacity of the entire mitochondrial network. Increasing the strength of the ATFS-1 MTS impaired UPRmt activity throughout development due to increased accumulation within mitochondria. The insulin-like signaling-TORC13 and AMPK pathways affected UPRmt activation4,5 in a manner that correlated with protein synthesis. Manipulation to increase protein synthesis caused UPRmt activation. Alternatively, S6 kinase inhibition had the opposite effect due to increased mitochondrial accumulation of ATFS-1. However, ATFS-1 with a dysfunctional MTS6 constitutively increased UPRmt activity independent of TORC1 function. Lastly, expression of a single protein with a strong MTS, was sufficient to expand the muscle cell mitochondrial network in an ATFS-1-dependent manner. We propose that mitochondrial network expansion during development is an emergent property of the synthesis of highly expressed mitochondrial proteins that exclude ATFS-1 from mitochondrial import, causing UPRmt activation. Mitochondrial network expansion is attenuated once ATFS-1 can be imported.

molecular biology↗