Biology subjects

Haynes, C. M.

Publications and source records attributed to Haynes, C. M..

6 recordsLinked to original sources

bioRxiv2026

Impaired Endosomal Recycling of Signaling Receptors Activates an Extracellular UPR

Mitochondrial dysfunction and extracellular protein aggregation occur in neurodegenerative diseases such as Alzheimers disease (AD). However, it remains unclear if these processes are functionally linked. Here, we identify a signaling pathway that is activated upon accumulation of aggregation-prone proteins in the extracellular space. We find that the transcription factor ATFS-1, which regulates the mitochondrial unfolded protein response, also regulates transcripts required for endosomal recycling, multiple plasma membrane-localized signaling receptors, and secreted proteins that bind aggregation-prone proteins in the extracellular space, including transthyretin and A{beta}, and promote their degradation. Interestingly, A{beta}(1-42) aggregation induces atfs-1-dependent transcription by promoting degradation of the bZIP protein ZIP-3, which antagonizes ATFS-1. ZIP-3 accumulates in the cytosol when it is phosphorylated by kinases that function downstream of plasma membrane-localized signaling receptors, including the WNT and glutamate receptors. Upon ligand binding, the signaling receptors stimulate the cognate kinase, many of which we found phosphorylate ZIP-3, impeding ZIP-3 degradation, allowing it to antagonize atfs-1-dependent transcription. However, accumulation of aggregation-prone proteins such as A{beta}(1-42) causes endosomal swelling, which impairs endosomal recycling, instead diverting signaling receptors to lysosomes for degradation. In turn, the depletion of signaling receptors reduces the level of ZIP-3 phosphorylation, resulting in ZIP-3 degradation and activation of atfs-1-dependent transcription, which promotes extracellular proteostasis. Our findings uncover an unexpected coupling between endocytic quality control and mitochondrial signaling, revealing a circuit that preserves extracellular proteostasis and promotes organismal resilience.

cell biology↗

bioRxiv2026

LONP-1 deficiency causes dysregulated protein synthesis within mitochondria that is restored by mitoribosomal mutations

Mitochondrial homeostasis is maintained by multiple molecular chaperones and proteases located within the organelle. The mitochondrial matrix-localized protease LONP-1 degrades oxidatively damaged or misfolded proteins. Importantly, LONP-1 also regulates mitochondrial DNA replication. Here, we show that mutations in C. elegans that impair LONP-1 function cause dysregulation of mitochondrial DNA replication, mitochondrial RNA transcription and protein synthesis within the mitochondrial matrix. LONP-1 deficient worms had reduced levels of oxidative phosphorylation proteins despite increased mtDNA-encoded protein synthesis. Via a forward genetic screen, we identified three mutations that restored mitochondrial function and the rate of development in lonp-1 mutants to levels comparable to those in wildtype worms. Interestingly, all three suppressor mutations were found in genes encoding mitochondrial ribosome proteins. A point mutation in the mitochondrial ribosome protein MRPS-38 restored oxidative phosphorylation in lonp-1 mutant worms. Combined, our results suggest that LONP-1 regulates mitochondrial protein synthesis and that the suppressor mutations within MRPS-38 or MRPS-15 enhance oxidative phosphorylation complex assembly by slowing translation.

cell biology↗

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↗

bioRxiv2020

The ESCRT protein CHMP5 restrains skeletal progenitor cell senescence by preserving endo-lysosomal-mitochondrial network

The dysfunction of the cellular endolysosomal pathway, such as in lysosomal storage diseases, can cause severe musculoskeletal disorders. However, how endolysosomal dysfunction causes musculoskeletal abnormalities remains poorly understood, limiting therapeutic options. Here, we report that CHMP5, a member of the endosomal sorting complex required for transport (ESCRT)-III protein family, is essential to maintain the endolysosomal pathway and regulate bone formation in osteogenic lineage cells. Genetic ablation of Chmp5 in mouse osteogenic cells increases bone formation in vivo and in vitro. Mechanistically, Chmp5 deletion causes endolysosomal dysfunction by decreasing the VPS4A protein, and CHMP5 overexpression is sufficient to increase the VPS4A protein. Subsequently, endolysosomal dysfunction disturbs mitochondrial functions and increases mitochondrial ROS, ultimately resulting in skeletal cell senescence. Senescent skeletal cells cause abnormal bone formation by combining cell-autonomous and paracrine actions. Importantly, the elimination of senescent cells using senolytic drugs can alleviate musculoskeletal abnormalities in Chmp5 conditional knockout mice. Therefore, our results show that cell senescence represents an underpinning mechanism and a therapeutic target for musculoskeletal disorders caused by the aberrant endolysosomal pathway, such as in lysosomal storage diseases. These results also uncover the function and mechanism of CHMP5 in the regulation of cell senescence by affecting the endolysosomal-mitochondrial pathway.

cell biology↗

bioRxiv2018

Cardioprotection by the Mitochondrial Unfolded Protein Response is Mediated by ATF5

The mitochondrial unfolded protein response (UPRmt)1 is a cytoprotective signaling pathway triggered by mitochondrial dysfunction. Activation of the UPRmt upregulates nuclear-encoded mitochondrial genes, including those for chaperones, proteases, and antioxidants, as well as glycolysis, to restore proteostasis and cell energetics. Activating transcription factor 5 (ATF5), a protein with both mitochondrial and nuclear targeting sequences, is proposed to mediate mammalian UPRmt signaling. Since proteostasis and bioenergetics are important in the response of organs such as the heart to injury, we hypothesized that pharmacologic UPRmt activation may be cardioprotective against ischemia-reperfusion (IR) injury and that such protection would require ATF5. Using a perfused heart IR injury model in wild-type and global Atf5-/- mice, we found that in-vivo administration of the UPRmt inducers oligomycin or doxycycline 6 h prior to ex-vivo IR injury was cardioprotective. Such protection was absent in hearts from Atf5-/- mice, and no protection was observed with acute ex-vivo cardiac administration of doxycycline. Loss of ATF5 also did not alter baseline IR injury (without UPRmt induction). Cardiac gene expression analysis by RNA-Seq revealed mild induction of numerous genes in an ATF5-dependent manner, which may be important for cardioprotection. Analysis of hearts by qPCR showed that oligomycin at 6 h significantly induced genes encoding ATF5 and several known UPRmt-linked proteins. We conclude that ATF5 is required for cardioprotection induced by drugs that activate the UPRmt.

cell biology↗