Mitochondrial Stress Response Research Articles

Abstract 5262: MBO enhances anti-tumor immunity in pancreatic ductal adenocarcinoma by inducing immunogenic apoptosis

Abstract Pancreatic ductal adenocarcinoma (PDAC) poses significant therapeutic challenges due to its aggressive nature and limited treatment options. In this study, we explored the anti-cancer potential of MBO, a compound selected through drug repurposing strategy based on its cytotoxic ability and modulation of key survival pathways in PDAC. Our preliminary in vitro experiments demonstrated MBO's potent cytotoxicity against various PDAC cell lines, inhibiting cellular growth and clonogenicity. MBO induced G1 phase cell cycle arrest in a concentration-dependent manner. In the next step, in vivo, studies using xenograft and orthotopic mouse models confirmed MBO's ability to suppress tumor growth and increase CD8+ T cell infiltration. MBO demonstrated a favorable tumor suppressive activity wherein it suppressed tumor growth by approximately 49% and 56% in xenograft and orthotopic models, respectively. A CD8+ T cell depletion experiment revealed partial dependence on CD8+ T cells for MBO's overall anti-tumor efficacy. Further, combining MBO with anti-PD1 therapy exhibited a synergistic effect, enhancing overall T cell infiltration, particularly CD8+ T cells. Our mechanistic studies revealed that MBO induced immunogenic apoptosis, as evidenced by increased expression of immunogenic cell death markers (HSP90 and calreticulin) and apoptotic markers. To further delineate the mechanism, we performed RPPA profiling. RPPA analysis indicated MBO's impact on mitochondrial gene expression and stress response pathways, suggesting its involvement in disrupting cellular survival mechanisms along with stress-induced immunogenic marker expression. Overall, this study demonstrates MBO as a promising anti-cancer agent with the potential to serve as an immune adjuvant. Particularly, in combination with immunotherapies, MBO can serve as a potential option to improve immunotherapeutic response in PDAC tumors providing valuable insights for developing novel therapeutic strategies in PDAC. Citation Format: Shreyas Ramchandra Gaikwad, Sanjay K. Srivastava. MBO enhances anti-tumor immunity in pancreatic ductal adenocarcinoma by inducing immunogenic apoptosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5262.

SIRT3: A Potential Target of Different Types of Osteoporosis.

Osteoporosis (OP) is a common age-related disease. OP is mainly a decrease in bone density and mass caused by the destruction of bone microstructure, which leads to an increase in bone fragility. SIRT3 is a mitochondrial deacetylase that plays critical roles in mitochondrial homeostasis, metabolic regulation, gene transcription, stress response, and gene stability. Studies have shown that the higher expression levels of SIRT3 are associated with decreased levels of oxidative stress in the body and may play important roles in the prevention of age-related diseases. SIRTs can enhance the osteogenic potential and osteoblastic activity of bone marrow mesenchymal stromal cells not only by enhancing PGC-1α, FOXO3, SOD2, and oxidative phosphorylation, but also by anti-aging and reducing mitochondrial autophagy. SIRT3 is able to upregulate antioxidant enzymes to exert an inhibitory effect on osteoclasts, however, it has been shown that the inflammatory cascade response can in turn increase SIRT3 and inhibit osteoclast differentiation through the AMPK-PGC-1β pathway. SIRT3 plays an important role in different types of osteoporosis by affecting osteoblasts, osteoclasts, and bone marrow mesenchymal cells. In this review, we discuss the classification and physiological functions of SIRTs, the effects of SIRT3 on OCs osteoblasts, and BMSCs, and the roles and mechanisms of SIRT3 in different types of OP, such as diabetic OP, glucocorticoid-induced OP, postmenopausal OP, and senile OP.

Suppression of microRNA-320 Induces Cerebral Protection Against Ischemia/Reperfusion Injury by Targeting HMGB1/NF-kappaB Axis.

MicroRNAs have been shown to potentially function in cerebral ischemia/reperfusion (IR) injury. This study aimed to examine the expression of microRNA-320 (miR-320) in cerebral IR injury and its involvement in cerebral mitochondrial function, oxidative stress, and inflammatory responses by targeting the HMGB1/NF-kappaB axis. Sprague-Dawley rats were subjected to middle cerebral artery occlusion to simulate cerebral IR injury. The cerebral expression of miR-320 was assessed using qRT-PCR. Neurological function, cerebral infarct volume, mitochondrial function, oxidative stress, and inflammatory cytokines were evaluated using relevant methods, including staining, fluorometry, and ELISA. HMGB1 expression was analyzed through Western blotting. The levels of miR-320, HMGB1, neurological deficits, and cerebral infarction were significantly higher after IR induction. Intracerebral overexpression of miR-320 resulted in substantial neurological deficits, increased infarct volume, elevated levels of 8-isoprostane, NF-kappaBp65, TNF-alpha, IL-1beta, ICAM-1, VCAM-1, and HMGB1 expression. It also promoted the loss of mitochondrial membrane potential and ROS levels while reducing MnSOD and GSH levels. Downregulation of miR-320 and inhibition of HMGB1 activity significantly reversed the outcomes of cerebral IR injury. MiR-320 plays a negative role in regulating cerebral inflammatory/oxidative reactions induced by IR injury by enhancing HMGB1 activity and modulating mitochondrial function.

A SIFI odyssey: Silencing the stress response amid mitochondrial import blockade to safeguard cell survival

In a recent study in Nature, Haakonsen etal.1 identify the SIFI complex as a stress response silencer via its E3 ligase activity to target unimported mitochondrial proteins and stress response components for degradation via the proteasome.

Safety and tolerability of phenylbutyrate in inclusion body myositis

Introduction
 Phenylbutyrate (PBA) showed positive effect on the muscle cell model of Inclusion Body Myositis (IBM) by improving lysosomal activity, ameliorating consequences of impaired autophagy, and decreasing vacuolization. This provides rationale to study this medication in patients with IBM.
 Objectives
 To evaluate the safety and tolerability of phenylbutyrate in IBM, and monitor for any early signal of effectiveness.
 Methods
 Open-label study of 10 subjects with IBM who received treatment with PBA for 3 months after a 3-month run-in period. The PBA dose was 3 gm twice daily. The primary outcome measure was adverse event reporting. Secondary outcome measures included manual muscle testing, timed up and go test, IBM functional rating scale, and grip strength, along with exploratory biomarkers evaluating the mitochondrial function, stress response, degenerative process, and apoptosis.
 Results
 Ten subjects completed the study. PBA was well tolerated with no serious adverse events related to it. The most common adverse events were gastrointestinal related and did not require stopping treatment. One of the biomarkers (MitoTracker) showed a statistically significant drop over the treatment period of the study (p-value of 0.02 for the mean change). There were no statistically significant changes in other secondary outcome measures, but the study was limited by a small sample size and short treatment period.
 Conclusions
 Phenylbutyrate was safe and well tolerated in patients with IBM in this pilot study. The change in the MitoTracker suggests target engagement, but a Phase II study is needed to confirm and study the efficacy of PBA in IBM

Sirtuin 3 (SIRT3) improves sevoflurane-induced postoperative cognitive impairment by regulating mitochondrial oxidative stress.

One of the most prevalent co-operative disorders is postoperative cognitive dysfunction (POCD), however, its pathogenesis remains unclear. Thus, the aim of this work was to evaluate SIRT3's impact on cognitive decline in aged mice under anesthesia. Adeno-associated virus SIRT3 vector (AAV-SIRT3) or empty vector (AAV-VEH) was injected into the hippocampal region of aged mice after sevoflurane induction in order to upregulate the expression of SIRT3. The expression levels of SIRT3, pro-inflammatory cytokines, and apoptotic factors in hippocampus tissues were identified by PCR, Western blotting, TUNEL staining, and enzyme-linked immunosorbent assay (ELISA), and the cognitive function of mice was assessed. The SIRT3 expression was down-regulated in the hippocampal tissue of anesthetized mice. SIRT3 overexpression can improve the learning and memory ability, reduce the escape latency, and increase the residence time in the platform and platform crossing ability of mice. The overexpression of SIRT3 in hippocampus can reduce the oxidative stress response and inflammatory response induced by anesthesia in mice, increase the superoxide dismutase (SOD) expression level, and decrease the expression level of MDA and inflammatory factors in hippocampus. In addition, SIRT3 overexpression can also reduce anesthetic-induced hippocampal cell apoptosis. By reducing the hippocampus mitochondrial oxidative stress response, SIRT3 plays a significant role in the pathophysiology of POCD in mice and is a potential target for POCD treatment and diagnosis.

Mitochondrial Unfolded Protein Response Gene Clpp Is Required for Oocyte Function and Female Fertility.

Mitochondrial unfolded protein stress response (mtUPR) plays a critical role in regulating cellular and metabolic stress response and helps maintain protein homeostasis. Caseinolytic peptidase P (CLPP) is one of the key regulators of mtUPR and promotes unfolded protein degradation. Previous studies demonstrated that global deletion of Clpp resulted in female infertility, whereas no impairment was found in the mouse model with targeted deletion of Clpp in cumulus/granulosa cells. These results suggest the need to delineate the function of Clpp in oocytes. In this study, we aimed to further explore the role of mtUPR in female reproductive competence and senescence using a mouse model. Oocyte-specific targeted deletion of Clpp in mice resulted in female subfertility associated with metabolic and functional abnormalities in oocytes, thus highlighting the importance of CLPP-mediated protein homeostasis in oocyte competence and reproductive function.

Abstract TP316: Treatment With Tamoxifen, a Selective Estrogen Receptor Modulator, Has a Cell Type-Specific Effect on Mitochondrial Stress From Oxygen Glucose Deprivation in Astrocytes and Microglia

Introduction: Tamoxifen (TAM), a selective estrogen receptor modulator, is a first-line treatment to prevent recurrence of hormone receptor positive breast cancer. Stroke risk is increased in women with low estrogen and doubles in women after the age of 55 (average age of menopause). Critically, women taking TAM as breast cancer therapy had increased risk of ischemic stroke (82%). We hypothesize treatment with TAM will increase stroke severity, which is associated with increased blood brain barrier (BBB) damage and worsened neuroinflammation. We investigated effects of TAM on mitochondrial stress and cellular function in astrocytes and microglia, key cells of the BBB and neuroimmune response, respectively. Methods: Cultured female human astrocytes and HMC3 microglia were treated with TAM (1uM), 17ß-estradiol (10nM, E2), or vehicle (DMSO) for 24 hours. Cells were separated into two groups: normoxic (21% O 2 , 25mM glucose) or oxygen and glucose deprivation (OGD) conditions 6 hours before analysis. Mitochondrial function was assessed using a Seahorse XFe96 Analyzer. Microglial expression of mitochondrial proteins (Complex I & III and DRP1) was analyzed with western blot, and function was assessed with flow cytometry after in vitro phagocytosis of pHrodo red zymosan. Results: TAM reduced maximal (p =0.0174) and basal respiration (p =0.0149) under OGD conditions in microglia compared with DMSO or E2 treatment. However, in astrocytes, maximal and basal respiration were increased in OGD (p =0.0003, p =0.0002). There was no significant difference in expression of mitochondrial proteins or phagocytic function in HMC3 microglia under either normoxic or OGD conditions after TAM treatment. Conclusions: TAM treatment resulted in a cell type-specific alteration in mitochondrial stress response. Since mitochondrial stress is a hallmark of stroke pathophysiology, and microglia and astrocytes are among the earliest cells to respond to ischemia, treatment with tamoxifen might alter the cellular environment, by its divergent actions on these two cell types, leading to worsened stroke outcomes. These data support the need for in vivo investigation to elucidate the mechanism by which TAM is altering cellular response. Support: RFAG042189 to FS, 1F30NS131053 to MEZ

P17/C18-ceramide-mediated mitophagy is an endogenous neuroprotective response in preclinical and clinical brain injury.

Repeat concussions (or repetitive mild traumatic brain injury [rmTBI]) are complex pathological processes consisting of a primary insult and long-term secondary complications and are also a prerequisite for chronic traumatic encephalopathy (CTE). Recent evidence implies a significant role of autophagy-mediated dysfunctional mitochondrial clearance, mitophagy, in the cascade of secondary deleterious events resulting from TBI. C18-ceramide, a bioactive sphingolipid produced in response to cell stress and damage, and its synthesizing enzyme (CerS1) are precursors to selective stress-mediated mitophagy. A transporter, p17, mediates the trafficking of CerS1, induces C18-ceramide synthesis in the mitochondrial membrane, and acts as an elimination signal in cell survival. Whether p17-mediated mitophagy occurs in the brain and plays a causal role in mitochondrial quality control in secondary disease development after rmTBI are unknown. Using a novel repetitive less-than-mild TBI (rlmTBI) injury paradigm, ablation of mitochondrial p17/C18-ceramide trafficking in p17 knockout (KO) mice results in a loss of C18-ceramide-induced mitophagy, which contributes to susceptibility and recovery from long-term secondary complications associated with rlmTBI. Using a ceramide analog with lipid-selenium conjugate drug, LCL768 restored mitophagy and reduced long-term secondary complications, improving cognitive deficits in rlmTBI-induced p17KO mice. We obtained a significant reduction of p17 expression and a considerable decrease of CerS1 and C18-ceramide levels in cortical mitochondria of CTE human brains compared with age-matched control brains. These data demonstrated that p17/C18-ceramide trafficking is an endogenous neuroprotective mitochondrial stress response following rlmTBI, thus suggesting a novel prospective strategy to interrupt the CTE consequences of concussive TBI.

Stress response silencing by an E3 ligase mutated in neurodegeneration

Stress response pathways detect and alleviate adverse conditions to safeguard cell and tissue homeostasis, yet their prolonged activation induces apoptosis and disrupts organismal health1–3. How stress responses are turned off at the right time and place remains poorly understood. Here we report a ubiquitin-dependent mechanism that silences the cellular response to mitochondrial protein import stress. Crucial to this process is the silencing factor of the integrated stress response (SIFI), a large E3 ligase complex mutated in ataxia and in early-onset dementia that degrades both unimported mitochondrial precursors and stress response components. By recognizing bifunctional substrate motifs that equally encode protein localization and stability, the SIFI complex turns off a general stress response after a specific stress event has been resolved. Pharmacological stress response silencing sustains cell survival even if stress resolution failed, which underscores the importance of signal termination and provides a roadmap for treating neurodegenerative diseases caused by mitochondrial import defects.

The Imipridone ONC213 Targets α-Ketoglutarate Dehydrogenase to Induce Mitochondrial Stress and Suppress Oxidative Phosphorylation in Acute Myeloid Leukemia.

In AML cells, ONC213 suppresses αKGDH, which induces a unique mitochondrial stress response, and reduces MCL1 to decrease oxidative phosphorylation and elicit potent antileukemia activity. See related commentary by Boët and Sarry, p. 950.

Loss of WDR23 proteostasis impacts mitochondrial homeostasis in the mouse brain

Mitochondrial adaptation is important for stress resistance throughout life. Here we show that WDR23 loss results in an enrichment for genes regulated by nuclear respiratory factor 1 (NRF1), which coordinates mitochondrial biogenesis and respiratory functions, and an increased steady state level of several nuclear coded mitochondrial resident proteins in the brain. Wdr23KO also increases the endogenous levels of insulin degrading enzyme (IDE) and the relaxin-3 peptide (RLN3), both of which have established roles in mediating mitochondrial metabolic and oxidative stress responses. Taken together, these studies reveal an important role for WDR23 as a component of the mitochondrial homeostat in the murine brain.

Mitochondrial Stress and Mitokines: Therapeutic Perspectives for the Treatment of Metabolic Diseases.

Mitochondrial stress and the dysregulated mitochondrial unfolded protein response (UPRmt) are linked to various diseases, including metabolic disorders, neurodegenerative diseases, and cancer. Mitokines, signaling molecules released by mitochondrial stress response and UPRmt, are crucial mediators of inter-organ communication and influence systemic metabolic and physiological processes. In this review, we provide a comprehensive overview of mitokines, including their regulation by exercise and lifestyle interventions and their implications for various diseases. The endocrine actions of mitokines related to mitochondrial stress and adaptations are highlighted, specifically the broad functions of fibroblast growth factor 21 and growth differentiation factor 15, as well as their specific actions in regulating inter-tissue communication and metabolic homeostasis. Finally, we discuss the potential of physiological and genetic interventions to reduce the hazards associated with dysregulated mitokine signaling and preserve an equilibrium in mitochondrial stress-induced responses. This review provides valuable insights into the mechanisms underlying mitochondrial regulation of health and disease by exploring mitokine interactions and their regulation, which will facilitate the development of targeted therapies and personalized interventions to improve health outcomes and quality of life.

Mic19 depletion impairs endoplasmic reticulum-mitochondrial contacts and mitochondrial lipid metabolism and triggers liver disease

Endoplasmic reticulum (ER)-mitochondria contacts are critical for the regulation of lipid transport, synthesis, and metabolism. However, the molecular mechanism and physiological function of endoplasmic reticulum-mitochondrial contacts remain unclear. Here, we show that Mic19, a key subunit of MICOS (mitochondrial contact site and cristae organizing system) complex, regulates ER-mitochondria contacts by the EMC2-SLC25A46-Mic19 axis. Mic19 liver specific knockout (LKO) leads to the reduction of ER-mitochondrial contacts, mitochondrial lipid metabolism disorder, disorganization of mitochondrial cristae and mitochondrial unfolded protein stress response in mouse hepatocytes, impairing liver mitochondrial fatty acid β-oxidation and lipid metabolism, which may spontaneously trigger nonalcoholic steatohepatitis (NASH) and liver fibrosis in mice. Whereas, the re-expression of Mic19 in Mic19 LKO hepatocytes blocks the development of liver disease in mice. In addition, Mic19 overexpression suppresses MCD-induced fatty liver disease. Thus, our findings uncover the EMC2-SLC25A46-Mic19 axis as a pathway regulating ER-mitochondria contacts, and reveal that impairment of ER-mitochondria contacts may be a mechanism associated with the development of NASH and liver fibrosis.

Mitochondrial metallopeptidase OMA1 in cancer.

Our understanding of the roles that mitochondria play in cellular physiology has evolved drastically-from a mere cellular energy supplier to a crucial regulator of metabolic and signaling processes, particularly in the context of development and progression of human diseases such as cancers. The present review examines the role of OMA1, a conserved, redox-sensitive metallopeptidase in cancer biology. OMA1's involvement in mitochondrial quality control, redox activity, and stress responses underscores its potential as a novel target in cancer diagnosis and treatment. However, our incomplete understanding of OMA1's regulation and structural detail presents ongoing challenges to target OMA1 for therapeutic purposes. Further exploration of OMA1 holds promise in uncovering novel insights into cancer mechanisms and therapeutic strategies. In this chapter, we briefly summarize our current knowledge about OMA1, its redox-regulation, and emerging role in certain cancers.

Molecular mechanism of tolerance evolution in Candida tropicalis to inhibitory compounds derived from corn stover hydrolysis

Candida tropicalis is distinguished from Saccharomyces cerevisiae by its great xylose utilization ability, maximizing its capability to ferment both hexoses and xylose to produce high-value products, and its ability to overcome the problem of end-product inhibition derived from lignocellulosic hydrolysis. However, little or no information about the molecular evolution mechanism of C. tropicalis to inhibitory compounds (acetic acid, phenol, and furfural) derived from lignocellulosic hydrolysis is known. In this study, the adaptation of a C. tropicalis strain SHC-03 to corn stover hydrolysate after mutagenesis through stepwise evolution resulted in multi-generation evolved strains after 60 rounds of evolution using the C. tropicalis strain SHC-03 as the parental strain. The evolved strain, generation B-60, (GB-60) showed the highest tolerance (15.81 g/L) and resistance as well as the lowest subcellular damage to inhibitory compounds derived from corn stover hydrolysis. Comparative transcriptome and genomic analyses between the evolved strain GB-60 and the control strain SHC-03 revealed enhanced functional and mutated genes including CTRG_03726, CTRG_01923, CTRG_04945, CTRG_05115, CTRG_03102, CTRG_05127, CTRG_00952 and CTRG_03034 involved in increased cell wall biosynthesis and remodeling, pentose phosphate pathway, metabolic and carbon pathways, detoxification of inhibitory compounds, and the multidrug/multixenobiotic resistance (MDR/MXR) transporters. These genes also played active roles in oxidative stress response, mitochondrial stress response, ER stress response, vacuole stress response and autophagy, DNA repair, and chromatin protection resulting in less ROS accumulation, as well as lower damage to some subcellular organelles in the evolved strain. The information from this study will provide guidelines for the development of engineering strains with high tolerance towards inhibitors derived from corn stover hydrolysis.

The slow-release adiponectin analog ALY688-SR modifies early-stage disease development in the D2.mdx mouse model of Duchenne muscular dystrophy.

Fibrosis is associated with respiratory and limb muscle atrophy in Duchenne muscular dystrophy (DMD). Current standard of care partially delays the progression of this myopathy but there remains an unmet need to develop additional therapies. Adiponectin receptor agonism has emerged as a possible therapeutic target to lower inflammation and improve metabolism in mdx mouse models of DMD but the degree to which fibrosis and atrophy are prevented remain unknown. Here, we demonstrate that the recently developed slow-release peptidomimetic adiponectin analog, ALY688-SR, remodels the diaphragm of murine model of DMD on DBA background (D2.mdx) mice treated from days 7-28 of age during early stages of disease. ALY688-SR also lowered interleukin-6 (IL-6) mRNA but increased IL-6 and transforming growth factor-β1 (TGF-β1) protein contents in diaphragm, suggesting dynamic inflammatory remodeling. ALY688-SR alleviated mitochondrial redox stress by decreasing complex I-stimulated H2O2 emission. Treatment also attenuated fibrosis, fiber type-specific atrophy, and in vitro diaphragm force production in diaphragm suggesting a complex relationship between adiponectin receptor activity, muscle remodeling, and force-generating properties during the very early stages of disease progression in murine model of DMD on DBA background (D2.mdx) mice. In tibialis anterior, the modest fibrosis at this young age was not altered by treatment, and atrophy was not apparent at this young age. These results demonstrate that short-term treatment of ALY688-SR in young D2.mdx mice partially prevents fibrosis and fiber type-specific atrophy and lowers force production in the more disease-apparent diaphragm in relation to lower mitochondrial redox stress and heterogeneous responses in certain inflammatory markers. These diverse muscle responses to adiponectin receptor agonism in early stages of DMD serve as a foundation for further mechanistic investigations.NEW & NOTEWORTHY There are limited therapies for the treatment of Duchenne muscular dystrophy. As fibrosis involves an accumulation of collagen that replaces muscle fibers, antifibrotics may help preserve muscle function. We report that the novel adiponectin receptor agonist ALY688-SR prevents fibrosis in the diaphragm of D2.mdx mice with short-term treatment early in disease progression. These responses were related to altered inflammation and mitochondrial functions and serve as a foundation for the development of this class of therapy.

O-GlcNAc regulates the mitochondrial integrated stress response by regulating ATF4.

Accumulation of mitochondrial dysfunctional is a hallmark of age-related neurodegeneration including Alzheimer's disease (AD). Impairment of mitochondrial quality control mechanisms leading to the accumulation of damaged mitochondria and increasing neuronal stress. Therefore, investigating the basic mechanisms of how mitochondrial homeostasis is regulated is essential. Herein, we investigate the role of O-GlcNAcylation, a single sugar post-translational modification, in controlling mitochondrial stress-induced transcription factor Activating Transcription Factor 4 (ATF4). Mitochondrial dysfunction triggers the integrated stress response (ISRmt), in which the phosphorylation of eukaryotic translation initiation factor 2α results in the translation of ATF4. We used patient-derived induced pluripotent stem cells, a transgenic mouse model of AD, SH-SY5Y neuroblastoma and HeLa cell-lines to examine the effect of sustained O-GlcNAcase inhibition by Thiamet-G (TMG) on ISRmt using biochemical analyses. We show that TMG elevates ATF4 protein levels upon mitochondrial stress in SH-SY5Y neuroblastoma and HeLa cell-lines. An indirect downstream target of ATF4 mitochondrial chaperone glucose-regulated protein 75 (GRP75) is significantly elevated. Interestingly, knock-down of O-GlcNAc transferase (OGT), the enzyme that adds O-GlcNAc, in SH-SY5Y increases ATF4 protein and mRNA expression. Additionally, ATF4 target gene Activating Transcription Factor 5 (ATF5) is significantly elevated at both the protein and mRNA level. Brains isolated from TMG treated mice show elevated levels of ATF4 and GRP75. Importantly, ATF4 occupancy increases at the ATF5 promoter site in brains isolated from TMG treated mice suggesting that O-GlcNAc is regulating ATF4 targeted gene expression. Interestingly, ATF4 and GRP75 are not induced in TMG treated familial Alzheimer's Disease mice model. The same results are seen in a human in vitro model of AD. Together, these results indicate that in healthy conditions, O-GlcNAc regulates the ISRmt through regulating ATF4, while manipulating O-GlcNAc in AD has no effect on ISRmt.

Mitoribosomal synthetic lethality overcomes multidrug resistance in MYC-driven neuroblastoma

Mitochondria are central for cancer responses to therapy-induced stress signals. Refractory tumors often show attenuated sensitivity to apoptotic signaling, yet clinically relevant molecular actors to target mitochondria-mediated resistance remain elusive. Here, we show that MYC-driven neuroblastoma cells rely on intact mitochondrial ribosome (mitoribosome) processivity and undergo cell death following pharmacological inhibition of mitochondrial translation, regardless of their multidrug/mitochondrial resistance and stem-like phenotypes. Mechanistically, inhibiting mitoribosomes induced the mitochondrial stress-activated integrated stress response (ISR), leading to downregulation of c-MYC/N-MYC proteins prior to neuroblastoma cell death, which could be both rescued by the ISR inhibitor ISRIB. The ISR blocks global protein synthesis and shifted the c-MYC/N-MYC turnover toward proteasomal degradation. Comparing models of various neuroectodermal tumors and normal fibroblasts revealed overexpression of MYC proteins phosphorylated at the degradation-promoting site T58 as a factor that predetermines vulnerability of MYC-driven neuroblastoma to mitoribosome inhibition. Reducing N-MYC levels in a neuroblastoma model with tunable MYCN expression mitigated cell death induction upon inhibition of mitochondrial translation and functionally validated the propensity of neuroblastoma cells for MYC-dependent cell death in response to the mitochondrial ISR. Notably, neuroblastoma cells failed to develop significant resistance to the mitoribosomal inhibitor doxycycline over a long-term repeated (pulsed) selection. Collectively, we identify mitochondrial translation machinery as a novel synthetic lethality target for multidrug-resistant MYC-driven tumors.

Canagliflozin Greatly Improves Mitochondrial Stress Response in Proximal Tubular Cells (PTCs) of Mice with Combined Hypertension and Type 1 Diabetes

Canagliflozin Greatly Improves Mitochondrial Stress Response in Proximal Tubular Cells (PTCs) of Mice with Combined Hypertension and Type 1 Diabetes