Accumulation Of Dysfunctional Mitochondria Research Articles

Enhanced Parkin-mediated mitophagy mitigates adverse left ventricular remodelling after myocardial infarction: role of PR-364.

Almost 30% of survivors of myocardial infarction (MI) develop heart failure (HF), in part due to damage caused by the accumulation of dysfunctional mitochondria. Organelle quality control through Parkin-mediated mitochondrial autophagy (mitophagy) is known to play a role in mediating protection against HF damage post-ischaemic injury and remodelling of the subsequent deteriorated myocardium. This study has shown that a single i.p. dose (2 h post-MI) of the selective small molecule Parkin activator PR-364 reduced mortality, preserved cardiac ejection fraction, and mitigated the progression of HF. To reveal the mechanism of PR-364, a multi-omic strategy was deployed in combination with classical functional assays using in vivo MI and in vitro cardiomyocyte models. In vitro cell data indicated that Parkin activation by PR-364 increased mitophagy and mitochondrial biogenesis, enhanced adenosine triphosphate production via improved citric acid cycle, altered accumulation of calcium localization to the mitochondria, and initiated translational reprogramming with increased expression of mitochondrial translational proteins. In mice, PR-364 administered post-MI resulted in widespread proteome changes, indicating an up-regulation of mitochondrial metabolism and mitochondrial translation in the surviving myocardium. This study demonstrates the therapeutic potential of targeting Parkin-mediated mitophagy using PR-364 to protect surviving cardiac tissue post-MI from progression to HF.

Klf9 is essential for cardiac mitochondrial homeostasis.

Mitochondrial dynamics and mitophagy are intimately linked physiological processes that are essential for cardiac homeostasis. Here we show that cardiac Krüppel-like factor 9 (Klf9) is dysregulated in human and rodent cardiomyopathy. Both global and cardiac-specific Klf9-deficient mice displayed hypertrophic cardiomyopathy. Klf9 knockout led to mitochondrial disarray and fragmentation, impairing mitochondrial respiratory function in cardiomyocytes. Furthermore, cardiac Klf9 deficiency inhibited mitophagy, thereby causing accumulation of dysfunctional mitochondria and acceleration of heart failure in response to angiotensin II treatment. In contrast, cardiac-specific Klf9 transgene improved cardiac systolic function. Mechanistically, Klf9 knockout decreased the expression of PGC-1α and its target genes involved in mitochondrial energy metabolism. Moreover, Klf9 controlled the expression of Mfn2, thereby regulating mitochondrial dynamics and mitophagy. Finally, adeno-associated virus-mediated Mfn2 rescue in Klf9-CKO hearts improved cardiac mitochondrial and systolic function. Thus, Klf9 integrates cardiac energy metabolism, mitochondrial dynamics and mitophagy. Modulating Klf9 activity may have therapeutic potential in the treatment of heart failure.

The Impact of Sex Hormones on Renal Mitochondrial Bioenergetics in Aging

Introduction. Aging is accompanied by changes in multiple factors, such as accumulation of mitochondrial dysfunction and the decline of sex hormone levels throughout life. Females are generally protected from renal diseases until menopause, potentially as a result of the presence of female sex hormones. Sex hormones govern a plethora of crucial renal processes, including metabolism and mitochondrial bioenergetics. However, there remains a gap in knowledge regarding the role of sex hormones in mitochondrial bioenergetics in renal aging. We hypothesized in this study that removal of sex hormones will exacerbate the aging-induced decline in renal mitochondrial function. Methods. Male and female Sprague Dawley (SD) rats were randomly divided into groups, and gonadectomy or sham surgery was performed before 4 wks of age. At 6 and 12 months of age kidneys were perfused to remove blood, then cortical tissues were immediately collected for mitochondrial isolations using differential centrifugation or snap-frozen/fixed for biochemical assays. Spectrofluorimetry was utilized to measure mitochondrial membrane potential (ΔΨm) and H2O2 production using TMRM and Amplex Red. Seahorse assay was done to measure oxygen consumption rate (OCR). OriginPro was used for statistical analysis (two-way ANOVA with Holm-Sidak post hoc). Results. Male OCR parameters (basal, ADP-linked, maximal and spare capacity) were lower than OCR observed in females at both 6 and 12 months of age (p<0.05). Orchiectomy resulted in an increase in male OCR parameters at both ages (p<0.05); ovariectomy did not affect renal cortical OCR (p>0.05 for both ages). Of note, gonadectomy in males increased the OCR up to the female level (p>0.05 for both ages). Cortical mitochondrial ΔΨm displayed similar values at 6 months across all groups. However, at 12 months we report lower ΔΨm in males vs female shams (p<0.001). Of note, the male gonadectomy increased ΔΨm up to the level of female values, while ovariectomy had no effect (p=0.3). Female cortical H2O2 production was higher than in males (p<0.001), whereas ovariectomy lowered H2O2 at both time points (p<0.001), indicative of ΔΨm-independent ROS sources. Interestingly, the effect of testosterone on H2O2 production was dependent on age. At 6 months old, orchiectomy did not alter H2O2 production compared to shams, while at 12 months, orchiectomy led to higher H2O2 production (p<0.001). Conclusions. Renal mitochondrial OCR was found to be independent of age in either sex at 6 and 12 months of age. Gonadectomy data allowed us to speculate that testosterone suppresses renal OCR, and the decreased membrane potential in males is likely driving the OCR changes. The observed ΔΨm-independent sources of H2O2 remain to be explored in future experiments. These data established the impact of sex hormones on mitochondrial bioenergetics and will help elucidate sex-specific targets that can mitigate the effects of aging on kidney function. Funding for this project came from 1U54HL169191. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Role of mitochondria in doxorubicin-mediated cardiotoxicity: From molecular mechanisms to therapeutic strategies.

This comprehensive review delves into the pivotal role of mitochondria in doxorubicin-induced cardiotoxicity, a significant complication limiting the clinical use of this potent anthracycline chemotherapeutic agent. Doxorubicin, while effective against various malignancies, is associated with dose-dependent cardiotoxicity, potentially leading to irreversible cardiac damage. The review meticulously dissects the molecular mechanisms underpinning this cardiotoxicity, particularly focusing on mitochondrial dysfunction, a central player in this adverse effect. Central to the discussion is the concept of mitochondrial quality control, including mitochondrial dynamics (fusion/fission balance) and mitophagy. The review presents evidence linking aberrations in these processes to cardiotoxicity in doxorubicin-treated patients. It elucidates how doxorubicin disrupts mitochondrial dynamics, leading to an imbalance between mitochondrial fission and fusion, and impairs mitophagy, culminating in the accumulation of dysfunctional mitochondria and subsequent cardiac cell damage. Furthermore, the review explores emerging therapeutic strategies targeting mitochondrial dysfunction. It highlights the potential of modulating mitochondrial dynamics and enhancing mitophagy to mitigate doxorubicin-induced cardiac damage. These strategies include pharmacological interventions with mitochondrial fission inhibitors, fusion promoters, and agents that modulate mitophagy. The review underscores the promising results from preclinical studies while advocating for more extensive clinical trials to validate these approaches in human patients. In conclusion, this review offers valuable insights into the intricate relationship between mitochondrial dysfunction and doxorubicin-mediated cardiotoxicity. It underscores the need for continued research into targeted mitochondrial therapies as a means to improve the cardiac safety profile of doxorubicin, thereby enhancing the overall treatment outcomes for cancer patients.

One therapy to protect them all: Controlling diabetic eye disease in anterior and posterior segment via mitophagy‐activating drugs

Aims/Purpose: The accumulation of dysfunctional mitochondria has been implicated in the pathogenesis of diabetic eye disease through the impairment of mitochondrial quality control (MQC). This study aimed to investigate whether mitophagy‐activating drugs can alleviate pathology in the anterior and posterior ocular tissues of type‐1 diabetic mice.Methods: Mitophagy was evaluated in corneal and retinal tissues from diabetic mitophagy reporter mice (mitoQC‐Ins2Akita). The therapeutic potential of targeting mitophagy was evaluated by treating diabetic Ins2Akita mice with PIA‐01 (a PINK1‐independent mitophagy activator). Treatment was delivered orally between 4 and 8 months of diabetes. Ocular degenerative changes were evaluated by scotopic electroretinography (ERG), along with immunohistochemical analysis of retinal neurons and corneal cytoarchitecture.Results: Indicative of deteriorated MQC, mitophagy and mitochondrial transcription factor A (TFAM) positive mitochondrial nucleoids (which contain mtDNA) significantly decreased in the cornea and retina by 8 months of diabetes. Oral delivery of PIA‐01 restored TFAM+ mitochondrial nucleoids, leading to improved visual outcomes in Ins2Akita mice. In the retina, this was reflected by improved ERG responses (e.g. increased scotopic a‐wave and b‐wave amplitudes), while also protecting retinal neurons, including cone‐photoreceptors, synaptic structures, amacrine cells and retinal ganglion cells. This protection extended to the anterior segment, where PIA‐01 rescued corneal cytoarchitecture (basal epithelium and stroma) in diabetic mice.Conclusions: Diabetes progresses with deterioration of MQC in anterior and posterior ocular tissues. Rescuing MQC via mitophagy‐activating drugs may allow for multisystem therapies to control diabetic eye disease.

O-GlcNAc impacts mitophagy via the PINK1-dependent pathway.

The accumulation of dysfunctional mitochondria is an early feature of Alzheimer's disease (AD). The impaired turnover of damaged mitochondria increases reactive oxygen species production and lowers ATP generation, leading to cellular toxicity and neurodegeneration. Interestingly, AD exhibits a disruption in the global post-translational modification β-N-acetylglucosamine (O-GlcNAc). O-GlcNAc is a ubiquitous single sugar modification found in the nuclear, cytoplasmic, and mitochondrial proteins. Cells maintain a homeostatic level of O-GlcNAc by cycling the addition and removal of the sugar by O-GlcNAc transferase (OGT) or O-GlcNAcase (OGA), respectively. We used patient-derived induced pluripotent stem cells, a transgenic mouse model of AD, SH-SY5Y neuroblastoma cell lines to examine the effect of sustained O-GlcNAcase inhibition by Thiamet-G (TMG) or OGT deficiency on mitophagy using biochemical analyses. Here, we established an essential role for O-GlcNAc in regulating mitophagy (mitochondria-selective autophagy). Stimulating mitophagy using urolithin A (UA) decreases cellular O-GlcNAc and elevates mitochondrial O-GlcNAc. Sustained elevation in O-GlcNAcylation via pharmacologically inhibiting OGA using Thiamet-G (TMG) increases the mitochondrial level of mitophagy protein PTEN-induced kinase 1 (PINK1) and autophagy-related protein light chain 3 (LC3). Moreover, we detected O-GlcNAc on PINK1 and TMG increases its O-GlcNAcylation level. Conversely, decreasing cellular O-GlcNAcylation by knocking down OGT decreases both PINK1 protein expression and LC3 protein expression. Mitochondria isolated from CAMKII-OGT-KO mice also had decreased PINK1 and LC3. Moreover, human brain organoids treated with TMG showed significant elevation in LC3 compared to control. However, TMG-treated AD organoids showed no changes in LC3 expression. Collectively, these data demonstrate that O-GlcNAc plays a crucial role in the activation and progression of mitophagy, and this activation is disrupted in AD.

Role of mitochondria in doxorubicin-mediated cardiotoxicity: from molecular mechanisms to therapeutic strategies.

This comprehensive review delves into the pivotal role of mitochondria in doxorubicin-induced cardiotoxicity, a significant complication limiting the clinical use of this potent anthracycline chemotherapeutic agent. Doxorubicin, while effective against various malignancies, is associated with dose-dependent cardiotoxicity, potentially leading to irreversible cardiac damage. The review meticulously dissects the molecular mechanisms underpinning this cardiotoxicity, particularly focusing on mitochondrial dysfunction, a central player in this adverse effect. Central to the discussion is the concept of mitochondrial quality control (MQC), including mitochondrial dynamics (fusion/fission balance) and mitophagy. The review presents evidence linking aberrations in these processes to cardiotoxicity in doxorubicin-treated patients. It elucidates how doxorubicin disrupts mitochondrial dynamics, leading to an imbalance between mitochondrial fission and fusion, and impairs mitophagy, culminating in the accumulation of dysfunctional mitochondria and subsequent cardiac cell damage. Furthermore, the review explores emerging therapeutic strategies targeting mitochondrial dysfunction. It highlights the potential of modulating mitochondrial dynamics and enhancing mitophagy to mitigate doxorubicin-induced cardiac damage. These strategies include pharmacological interventions with mitochondrial fission inhibitors, fusion promoters, and agents that modulate mitophagy. The review underscores the promising results from preclinical studies while advocating for more extensive clinical trials to validate these approaches in human patients. In conclusion, this review offers valuable insights into the intricate relationship between mitochondrial dysfunction and doxorubicin-mediated cardiotoxicity. It underscores the need for continued research into targeted mitochondrial therapies as a means to improve the cardiac safety profile of doxorubicin, thereby enhancing the overall treatment outcomes for cancer patients.

Mitophagy induction improves salivary gland stem/progenitor cell function by reducing senescence after irradiation

Background and purposePatients undergoing radiotherapy for head and neck cancer often experience a decline in their quality of life due to the co-irradiation of salivary glands. Radiation-induced cellular senescence is a key factor contributing to salivary gland dysfunction. Interestingly, mitochondrial dysfunction and cellular senescence have been reported to be strongly interconnected and thus implicated in several aging-related diseases. This study aims to investigate the role of mitochondrial dysfunction in senescence induction in salivary gland stem/progenitor cells after irradiation. Materials and methodsA dose of 7 Gy photons was used to irradiate mouse salivary gland organoids. Senescent markers and mitochondrial function were assessed using rt-qPCR, western blot analysis, SA-β-Gal staining and flow cytometry analysis. Mitochondrial dynamics-related proteins were detected by western blot analysis while Mdivi-1 and MFI8 were used to modulate the mitochondrial fission process. To induce mitophagy, organoids were treated with Urolithin A and PMI and subsequently stem/progenitor cell self-renewal capacity was assessed as organoid forming efficiency. ResultsIrradiation led to increased senescence and accumulation of dysfunctional mitochondria. This was accompanied by a strong downregulation of mitochondrial fission-related proteins and mitophagy-related genes. After irradiation, treatment with the mitophagy inducer Urolithin A attenuated the senescent phenotype and improved organoid growth and stem/progenitor cell self-renewal capacity. ConclusionThis study shows the important interplay between senescence and mitochondrial dysfunction after irradiation. Importantly, activation of mitophagy improved salivary gland stem/progenitor cell function thereby providing a novel therapeutic strategy to restore the regenerative capacity of salivary glands following irradiation.

Autophagy ablation in skeletal muscles worsens sepsis-induced muscle wasting, impairs whole-body metabolism, and decreases survival

Septic patients frequently develop skeletal muscle wasting and weakness, resulting in severe clinical consequences and adverse outcomes. Sepsis triggers sustained induction of autophagy, a key cellular degradative pathway, in skeletal muscles. However, the impact of enhanced autophagy on sepsis-induced muscle dysfunction remains unclear. Using an inducible and muscle-specific Atg7 knockout mouse model (Atg7iSkM-KO), we investigated the functional importance of skeletal muscle autophagy in sepsis using the cecal ligation and puncture model. Atg7iSkM-KO mice exhibited a more severe phenotype in response to sepsis, marked by severe muscle wasting, hypoglycemia, higher ketone levels, and a decreased in survival as compared to mice with intact Atg7. Sepsis and Atg7 deletion resulted in the accumulation of mitochondrial dysfunction, although sepsis did not further worsen mitochondrial dysfunction in Atg7iSkM-KO mice. Overall, our study demonstrates that autophagy inactivation in skeletal muscles triggers significant worsening of sepsis-induced muscle and metabolic dysfunctions and negatively impacts survival.

Mitochondrial alterations in the cochlea of Cdk5rap1-knockout mice with age-related hearing loss.

Previous studies have revealed that age-related hearing loss (AHL) in Cdk5 regulatory subunit-associated protein 1 (Cdk5rap1)-knockout mice is associated with pathology in the cochlea. Here, we aimed to identify mitochondrial alterations in the cochlea of Cdk5rap1-knockout mice with AHL. Mitochondria in the spiral ganglion neurons (SGNs) and hair cells (HCs) were normal despite senescence; however, the mitochondria of types I, II, and IV spiral ligament fibrocytes were ballooned, damaged, and ballooned, respectively, in the stria vascularis. Our results suggest that the accumulation of dysfunctional mitochondria in the lateral wall, rather than the loss of HCs and SGNs, leads to the onset of AHL. Our results provide valuable information regarding the underlying mechanisms of AHL and the relationship between aberrant tRNA modification-induced hearing loss and mitochondrial dysfunction.

Abstract 300: Physiologic Oxygen Conditions Preserve Ipsc-ec Progenitor Identity

Background: Advanced peripheral artery disease (PAD) is characterized by disabling lower extremity pain at rest and non-healing wounds. Many patients are limited to palliation with major amputation. There remains a great need for improved therapeutic modalities to treat advanced PAD and prevent limb loss. Induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) have improved limb perfusion without surgery in pre-clinical mouse models. iPSC-ECs lose angiogenic capacity under standard culture conditions, currently limiting scalability for larger animals and humans. Our prior work demonstrated that this is driven by accumulation of dysfunctional mitochondria. The current study evaluates the effect of oxygen metabolism on driving angiogenic capacity of iPSC-ECs in culture. Methods and Results: Purified ECs, differentiated from the Y6 iPSC line (Yale Stem Cell Core), were sub-cultured under standard (21% oxygen) or physiologic (4% oxygen) conditions. In the early phase, after 24 hours, Y6-ECs under physiologic conditions had significantly lower NO synthase activity (DAF-FM assay, Invitrogen) (p<0.05). There were no significant differences in the remaining EC function metrics: tubule formation on Matrigel to assess angiogenesis, beta galactosidase for senescence, or Edu-labeling for proliferation. All early phase cells expressed EC progenitor marker CD34. In the late phase, after 2 weeks, the physiologic conditions retained progenitor marker CD34 and EC marker CD31 while the normoxic conditions did not. Despite this, physiologic conditions demonstrated decreased tubule formation by some but not all measures but did not differ from normoxic conditions in the other EC function metrics. Additionally, late phase cells had a significant increase in senescence compared to early phase cells (p<0.05). Conclusion: In summary, physiologic culture conditions promoted retention of EC progenitor marker CD34 over serial passages in culture. However, some but not all in vitro metrics of angiogenic capacity appeared reduced in physiologic conditions. Future studies will be necessary to investigate the in vivo angiogenic capacity of iPSC-ECs grown under physiologic conditions.

A TNFα/Miz1-positive feedback loop inhibits mitophagy in hepatocytes and propagates non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is a chronic inflammatory disease that can further progress to cirrhosis and hepatocellular carcinoma. However, the key molecular mechanisms behind this process have not been clarified. We analyzed human NASH and normal liver tissue samples by RNA-sequencing and liquid chromatography-mass spectrometry, identifying hepatocyte cytosolic protein Myc-interacting zinc-finger protein 1 (Miz1) as a potential target in NASH progression. We established a Western diet+fructose-induced NASH model in hepatocyte-specific Miz1 knockout and adeno-associated virus type 8-overexpressing mice. Human NASH liver organoids were used to confirm the mechanism, and immunoprecipitation and mass spectrometry were used to detect proteins that could interact with Miz1. We demonstrate that Miz1 is reduced in hepatocytes in human NASH. Miz1 is shown to bind to peroxiredoxin 6 (PRDX6), retaining it in the cytosol, blocking its interaction with mitochondrial Parkin at Cys431, and inhibiting Parkin-mediated mitophagy. In NASH livers, loss of hepatocyte Miz1 results in PRDX6-mediated inhibition of mitophagy, increased dysfunctional mitochondria in hepatocytes, and production of proinflammatory cytokines, including TNFα, by hepatic macrophages. Crucially, the increased production of TNFα results in a further reduction in hepatocyte Miz1 by E3-ubiquitination. This produces a positive feedback loop of TNFα-mediated hepatocyte Miz1 degradation, resulting in PRDX6-mediated inhibition of hepatocyte mitophagy, with the accumulation of dysfunctional mitochondria in hepatocytes and increased macrophage TNFα production. Our study identified hepatocyte Miz1 as a suppressor of NASH progression via its role in mitophagy; we also identified a positive feedback loop by which TNFα production induces degradation of cytosolic Miz1, which inhibits mitophagy and thus leads to increased macrophage TNFα production. Interruption of this positive feedback loop could be a strategy to inhibit the progression of NASH. Non-alcoholic steatohepatitis (NASH) is a chronic inflammatory disease that can further develop into cirrhosis and hepatocellular carcinoma. However, the key molecular mechanism of this process has not been fully clarified. Herein, we identified a positive feedback loop of macrophage TNFα-mediated hepatocyte Miz1 degradation, resulting in PRDX6-mediated inhibition of hepatocyte mitophagy, aggravation of mitochondrial damage and increased macrophage TNFα production. Our findings not only provide mechanistic insight into NASH progression but also provide potential therapeutic targets for patients with NASH. Our human NASH liver organoid culture is therefore a useful platform for exploring treatment strategies for NASH development.

Recent Advances in Mitochondrial Fission/Fusion-Targeted Therapy in Doxorubicin-Induced Cardiotoxicity.

Doxorubicin (DOX) has been recognized as one of the most effective chemotherapies and extensively used in the clinical settings of human cancer. However, DOX-mediated cardiotoxicity is known to compromise the clinical effectiveness of chemotherapy, resulting in cardiomyopathy and heart failure. Recently, accumulation of dysfunctional mitochondria via alteration of the mitochondrial fission/fusion dynamic processes has been identified as a potential mechanism underlying DOX cardiotoxicity. DOX-induced excessive fission in conjunction with impaired fusion could severely promote mitochondrial fragmentation and cardiomyocyte death, while modulation of mitochondrial dynamic proteins using either fission inhibitors (e.g., Mdivi-1) or fusion promoters (e.g., M1) can provide cardioprotection against DOX-induced cardiotoxicity. In this review, we focus particularly on the roles of mitochondrial dynamic pathways and the current advanced therapies in mitochondrial dynamics-targeted anti-cardiotoxicity of DOX. This review summarizes all the novel insights into the development of anti-cardiotoxic effects of DOX via the targeting of mitochondrial dynamic pathways, thereby encouraging and guiding future clinical investigations to focus on the potential application of mitochondrial dynamic modulators in the setting of DOX-induced cardiotoxicity.

Doxorubicin leads to cardiomyocyte death by causing the accumulation of dysfunctional mitochondria through its inhibition of the autophagy fusion process.

Doxorubicin leads to cardiomyocyte death by causing the accumulation of dysfunctional mitochondria through its inhibition of the autophagy fusion process.

The impact of high-fat feeding and parkin overexpression on skeletal muscle mass, mitochondrial respiration, and H2O2 emission.

Obesity is a major risk factor for developing various health problems, including insulin resistance and type 2 diabetes. Although controversial, accumulation of mitochondrial dysfunction, and notably an increase in mitochondrial reactive oxygen species (ROS) production, was proposed as a key contributor leading to obesity-induced insulin resistance. Here, our goal was to investigate whether Parkin overexpression, a key regulator of the removal of dysfunctional mitochondria through mitophagy, could confer protection against obesity-induced mitochondrial dysfunction. To this end, intramuscular injections of adeno-associated viruses (AAVs) were performed to overexpress Parkin in limb muscle of 6-mo-old mice fed a control diet (CD) or a high-fat diet (HFD) for 12 wk. An AAV-expressing the green fluorescent protein (GFP) was used as control. HFD increased fat mass, altered glycemia, and resulted in insulin resistance. Parkin overexpression resulted in an increase in muscle mass in both CD and HFD mice. In CD mice, Parkin overexpression increased maximal mitochondrial respiration and lowered H2O2 emission. HFD increased mitochondrial respiration and, surprisingly, also lowered H2O2 emission. Parkin overexpression did not significantly impact mitochondrial function in HFD mice. Taken altogether, our results indicate that Parkin overexpression positively impacts muscle and mitochondrial health under basal conditions and challenges the notion that intrinsic mitochondrial dysfunction is involved in the development of insulin resistance caused by high-fat feeding.

Abstract 12168: Pi3kγ is a Key Modulator of Cardiac Metabolism Rewiring Occurring in Doxorubicin-Treated Mice

Introduction: Doxorubicin (DOX) is a potent chemotherapeutic drug, whose use is hampered by the onset of long-term cardiotoxicity and lack of effective therapeutic approaches. Recently, metabolic perturbations have emerged as an early predictor factor of cardiac dysfunction, but how DOX affects cardiac metabolism is still unknown. We have previously demonstrated that phosphoinositide 3-kinase γ (PI3Kγ) is a major driver of DOX-evoked cardiotoxicity through mitophagy inhibition and accumulation of dysfunctional mitochondria. Hypothesis: Here we sought to explore the role of PI3Kγ in modulating cardiac metabolism upon DOX administration. Methods: Metabolomic analysis, glycolysis and oxidative phosphorylation were measured in whole hearts from wild-type (WT) and knock-in mice expressing a kinase-inactive PI3Kγ (kinase-dead; KD) treated with DOX (4 mg/kg on day 0, 7 and 14). Similar analyses were performed in WT and KD hearts infected with AAV9-shATG7 to explore the role of autophagy. Moreover, glucose uptake and GLUT-4 expression on the plasma membrane were measured in WT and KD neonatal mouse cardiomyocytes (NMCs) exposed to 1μM DOX. Results: Metabolomic analysis revealed an increased level of succinate and malic acid in DOX-treated hearts, suggesting defects in the TCA cycle. In agreement, DOX promotes the accumulation of metabolites normally catabolised in the TCA cycle, such as aminoacids and pyruvate, indicating a severe mitochondria dysfunction. Accordingly, fatty acid oxidation and electron transport chain activity were impaired in DOX-treated hearts at day 3 and exacerbated at day 42 after DOX. At the same time, glycolysis was upregulated. These changes were prevented in KD animals. Interestingly, upon autophagy inhibition, KD mice lost their cardioprotection at the mitochondrial level, but they still failed to upregulate glycolysis. This suggests a new autophagy-independent mechanism through which PI3Kγ regulates glucose utilisation. In agreement with the pharmacological and genetic inhibition of PI3Kγ abrogates glucose uptake in NMCs and normalises the plasma membrane exposure of GLUT-4. Conclusions: Overall, these results promote PI3Kγ as a master regulator of metabolic rewiring occurring in DOX-treated cardiomyocytes.

SIAH proteins regulate the degradation and intra-mitochondrial aggregation of PINK1: Implications for mitochondrial pathology in Parkinson's disease.

Parkinson's disease (PD) is characterized by degeneration of neurons, particularly dopaminergic neurons in the substantia nigra. PD brains show accumulation of α-synuclein in Lewy bodies and accumulation of dysfunctional mitochondria. However, the mechanisms leading to mitochondrial pathology in sporadic PD are poorly understood. PINK1 is a key for mitophagy activation and recycling of unfit mitochondria. The activation of mitophagy depends on the accumulation of uncleaved PINK1 at the outer mitochondrial membrane and activation of a cascade of protein ubiquitination at the surface of the organelle. We have now found that SIAH3, a member of the SIAH proteins but lacking ubiquitin-ligase activity, is increased in PD brains and cerebrospinal fluid and in neurons treated with α-synuclein preformed fibrils (α-SynPFF). We also observed that SIAH3 is aggregated together with PINK1 in the mitochondria of PD brains. SIAH3 directly interacts with PINK1, leading to their intra-mitochondrial aggregation in cells and neurons and triggering a cascade of toxicity with PINK1 inactivation along with mitochondrial depolarization and neuronal death. We also found that SIAH1 interacts with PINK1 and promotes ubiquitination and proteasomal degradation of PINK1. Similar to the dimerization of SIAH1/SIAH2, SIAH3 interacts with SIAH1, promoting its translocation to mitochondria and preventing its ubiquitin-ligase activity toward PINK1. Our results support the notion that the increase in SIAH3 and intra-mitochondrial aggregation of SIAH3-PINK1 may mediate α-synuclein pathology by promoting proteotoxicity and preventing the elimination of dysfunctional mitochondria. We consider it possible that PINK1 activity is decreased in sporadic PD, which impedes proper mitochondrial renewal in the disease.

Role of mitophagy in the neurodegenerative diseases and its pharmacological advances: A review

Neurodegenerative diseases are a class of incurable and debilitating diseases characterized by progressive degeneration and death of cells in the central nervous system. They have multiple underlying mechanisms; however, they all share common degenerative features, such as mitochondrial dysfunction. According to recent studies, neurodegenerative diseases are associated with the accumulation of dysfunctional mitochondria. Selective autophagy of mitochondria, called mitophagy, can specifically degrade excess or dysfunctional mitochondria within cells. In this review, we highlight recent findings on the role of mitophagy in neurodegenerative disorders. Multiple studies were collected, including those related to the importance of mitochondria, the mechanism of mitophagy in protecting mitochondrial health, and canonical and non-canonical pathways in mitophagy. This review elucidated the important function of mitophagy in neurodegenerative diseases, discussed the research progress of mitophagy in neurodegenerative diseases, and summarized the role of mitophagy-related proteins in neurological diseases. In addition, we also highlight pharmacological advances in neurodegeneration.

Neuronopathic Gaucher disease: Beyond lysosomal dysfunction.

Gaucher disease (GD) is an inherited disorder caused by recessive mutations in the GBA1 gene that encodes the lysosomal enzyme β-glucocerebrosidase (β-GC). β-GC hydrolyzes glucosylceramide (GluCer) into glucose and ceramide in the lysosome, and the loss of its activity leads to GluCer accumulation in different tissues. In severe cases, enzymatic deficiency triggers inflammation, organomegaly, bone disease, and neurodegeneration. Neuronopathic Gaucher disease (nGD) encompasses two different forms of the disease, characterized by chronic or acute damage to the central nervous system (CNS). The cellular and molecular studies that uncover the pathological mechanisms of nGD mainly focus on lysosomal dysfunction since the lysosome is the key organelle affected in GD. However, new studies show alterations in other organelles that contribute to nGD pathology. For instance, abnormal accumulation of GluCer in lysosomes due to the loss of β-GC activity leads to excessive calcium release from the endoplasmic reticulum (ER), activating the ER-associated degradation pathway and the unfolded protein response. Recent evidence indicates mitophagy is altered in nGD, resulting in the accumulation of dysfunctional mitochondria, a critical factor in disease progression. Additionally, nGD patients present alterations in mitochondrial morphology, membrane potential, ATP production, and increased reactive oxygen species (ROS) levels. Little is known about potential dysfunction in other organelles of the secretory pathway, such as the Golgi apparatus and exosomes. This review focuses on collecting evidence regarding organelle dysfunction beyond lysosomes in nGD. We briefly describe cellular and animal models and signaling pathways relevant to uncovering the pathological mechanisms and new therapeutic targets in GD.

Urolithin A attenuates auditory cell senescence by activating mitophagy

Aging of sensory organs is associated with a decline in mitochondrial function and the accumulation of dysfunctional mitochondria. Impaired mitophagy blocks the turnover of dysfunctional mitochondria and leads to their accumulation. Urolithin A (UA) induces mitophagy in various mammalian cells. This study was aimed at investigating the effect of the mitophagy activator, UA, on premature senescent auditory cells. The levels of cellular senescence-associated p53 and p21 significantly increased in H2O2-induced senescent House Ear Institute‐Organ of Corti 1 (HEI-OC1) cells and cochlear explants. However, the levels of mitophagy-related molecules significantly decreased. UA significantly decreased the expression of senescence-associated p53 and p21, and increased the expression of mitophagy-related proteins, in H2O2-induced senescent cells and cochlear explants. The percentage of β-galactosidase-stained senescent cells also reduced in H2O2-treated cells and cochlear explants upon UA pre-treatment. The formation of mitophagosomes and mitophagolysosomes was restored upon UA pre-treatment of H2O2-induced senescent cells. The knockdown of mitophagy-related genes (Parkin and Bnip3) resulted in annulment of UA-induced anti-senescent activity. UA significantly increased the ATP content, mitochondrial DNA (mtDNA) integrity, and mitochondrial membrane potential in senescent HEI-OC1 cells. These findings indicate that UA counteracted mitophagy decline and prevented premature senescence in auditory cells. Hence, UA administration might be a promising strategy for preventing mitochondrial dysfunction in patients with age-related hearing loss.