UPRmt scales mitochondrial network expansion with protein synthesis via mitochondrial import [preprint]

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

UPR(mt) scales mitochondrial network expansion with protein synthesis via mitochondrial import in Caenorhabditis elegans

As organisms develop, individual cells generate mitochondria to fulfill physiological requirements. However, it remains unknown how mitochondrial network expansion is scaled to cell growth. The mitochondrial unfolded protein response (UPR(mt)) is a signaling pathway mediated by the transcription factor ATFS-1 which harbors a mitochondrial targeting sequence (MTS). Here, using the model organism Caenorhabditis elegans we demonstrate that ATFS-1 mediates an adaptable mitochondrial network expansion program that is active throughout normal development. Mitochondrial network expansion requires the relatively inefficient MTS in ATFS-1, which allows the transcription factor to be responsive to parameters that impact protein import capacity of the mitochondrial network. Increasing the strength of the ATFS-1 MTS impairs UPR(mt) activity by increasing accumulation within mitochondria. Manipulations of TORC1 activity increase or decrease ATFS-1 activity in a manner that correlates with protein synthesis. Lastly, expression of mitochondrial-targeted GFP is 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 UPR(mt) activation

Five undescribed plant-derived bisphenols from Artemisia capillaris aerial parts: Structure elucidation, anti-hepatoma activities and plausible biogenetic pathway

Yin-Chen, which belongs to the Asteraceae family and the genus Artemisia, is among the most abundantly used traditional medicines in China for the treatment of hepatitis and bilious disorder. Herein, five undescribed plant-derived bisphenols, capillarisenols A–E (13, 15, 25, 29, 31), and one undescribed phenolic compound (32), together with 32 known phenolic compounds (1–12, 14, 16–24, 26–28, 30, 33–38), were isolated and identified based on spectroscopic evidence from aerial parts of Artemisia capillaris Thunb. Capillarisenols A–E are the type of bisphenols firstly isolated from this plant. The plausible biogenetic pathway of new compounds was also proposed. In addition, the potential anti-hepatoma effects on Huh7 and HepG2 cell lines of all isolated compounds were evaluated in vitro. Capillarisenol C (25) showed significant anti-hepatoma activity in Huh7 and HepG 2 cells, with IC50 values of 4.96 and 8.58 μM, better than the positive control drug (Lenvatinib). This study provided phytochemical evidence for further development and utilisation of A. capillaris in health products

Mitochondrial UPR repression during Pseudomonas aeruginosa infection requires the bZIP protein ZIP-3

Mitochondria generate most cellular energy and are targeted by multiple pathogens during infection. In turn, metazoans employ surveillance mechanisms such as the mitochondrial unfolded protein response (UPR(mt)) to detect and respond to mitochondrial dysfunction as an indicator of infection. The UPR(mt) is an adaptive transcriptional program regulated by the transcription factor ATFS-1, which induces genes that promote mitochondrial recovery and innate immunity. The bacterial pathogen Pseudomonas aeruginosa produces toxins that disrupt oxidative phosphorylation (OXPHOS), resulting in UPR(mt) activation. Here, we demonstrate that Pseudomonas aeruginosa exploits an intrinsic negative regulatory mechanism mediated by the Caenorhabditis elegans bZIP protein ZIP-3 to repress UPR(mt) activation. Strikingly, worms lacking zip-3 were impervious to Pseudomonas aeruginosa-mediated UPR(mt) repression and resistant to infection. Pathogen-secreted phenazines perturbed mitochondrial function and were the primary cause of UPR(mt) activation, consistent with these molecules being electron shuttles and virulence determinants. Surprisingly, Pseudomonas aeruginosa unable to produce phenazines and thus elicit UPR(mt) activation were hypertoxic in zip-3-deletion worms. These data emphasize the significance of virulence-mediated UPR(mt) repression and the potency of the UPR(mt) as an antibacterial response

Mitochondrial inorganic polyphosphate is required to maintain proteostasis within the organelle

The existing literature points towards the presence of robust mitochondrial mechanisms aimed at mitigating protein dyshomeostasis within the organelle. However, the precise molecular composition of these mechanisms remains unclear. Our data show that inorganic polyphosphate (polyP), a polymer well-conserved throughout evolution, is a component of these mechanisms. In mammals, mitochondria exhibit a significant abundance of polyP, and both our research and that of others have already highlighted its potent regulatory effect on bioenergetics. Given the intimate connection between energy metabolism and protein homeostasis, the involvement of polyP in proteostasis has also been demonstrated in several organisms. For example, polyP is a bacterial primordial chaperone, and its role in amyloidogenesis has already been established. Here, using mammalian models, our study reveals that the depletion of mitochondrial polyP leads to increased protein aggregation within the organelle, following stress exposure. Furthermore, mitochondrial polyP is able to bind to proteins, and these proteins differ under control and stress conditions. The depletion of mitochondrial polyP significantly affects the proteome under both control and stress conditions, while also exerting regulatory control over gene expression. Our findings suggest that mitochondrial polyP is a previously unrecognized, and potent component of mitochondrial proteostasis