GRAF1 integrates PINK1-Parkin signaling and actin dynamics to mediate cardiac mitochondrial homeostasis

PINK1 deficiency alleviates bleomycin-induced pulmonary fibrosis in mice

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive lung disorder marked by deteriorating dyspnea and declining pulmonary function. Despite its rising prevalence and incidence, therapeutic options remain limited. PTEN-induced kinase 1 (PINK1), known for its role in PINK1/Parkin-dependent mitophagy, contributes to the pathogenesis of various lung diseases. In this study, we elucidate a previously unrecognized mechanism of PINK1, beyond its canonical mitophagy function, during pulmonary fibrosis. We established a bleomycin (BLM)-induced pulmonary fibrosis model in Pink1 knockout (Pink1-/-) mice and treated BEAS-2B cells with transforming growth factor-beta 1 (TGF-β1) to simulate the microenvironment of pulmonary fibrosis. A significant elevation in PINK1 expression was observed in vivo and in vitro systems. While PINK1/Parkin-dependent mitophagy was activated, mitophagy mediated by BCL2-interacting protein 3 (BNIP3) and FUN14 domain-containing 1 (FUNDC1) was suppressed. Further experiments in carbonyl cyanide m-chlorophenyl hydrazone (CCCP)-treated PINK1 knockout (KO) HEK293 cells and YFP-Parkin-expressing HeLa cells demonstrated that PINK1 deficiency enhanced BNIP3- and FUNDC1-mediated mitophagy, whereas PINK1 overexpression inhibited it. Moreover, dual BNIP3/FUNDC1 knockdown significantly reversed the anti-apoptotic effect of PINK1 KO. We conclude that PINK1 deficiency promotes the clearance of damaged mitochondria via BNIP3/FUNDC1 upregulation, preserving mitochondrial homeostasis, mitigating alveolar epithelial injury, and attenuating fibrosis. Thus, PINK1 may inhibit BNIP3- and FUNDC1-mediated mitophagy besides driving PINK1-dependent mitophagy during pulmonary fibrosis.

Furin inhibits HSCs activation and ameliorates liver fibrosis by regulating PTEN-L/PINK1/parkin mediated mitophagy in mouse

Hepatic Stellate cells (HSCs) play an important role during liver fibrosis progression; more and more evidence indicates that mitophagy greatly regulates HSCs activation. HSCs mitophagy mainly depends on the classical PINK1/Parkin pathway, which can be strongly regulated by phosphatase PTEN-long (PTEN-L). PTEN-L can be cleaved by Furin that leading to functional changes in the tumor regulation process. However, the impact of the interaction between Furin and PTEN-L on HSCs mitophagy remains unclear. Therefore, this study aims to explore the role of Furin in HSCs activation and liver fibrosis and its potential mechanisms. Our results revealed that Furin expression was obviously up-regulated during HSCs activation and mice liver fibrogenesis. We also found that the activation of primary HSCs can be inhibited by Furin treatment in vitro. Besides, functional studies showed that LX-2 cell proliferation and migration were obviously inhibited by Furin treatment. Further studies showed that mitochondrial membrane potential (MMP) was significantly reduced by Furin treatment, and the knockdown of PTEN-L expression caused similar effects. These results demonstrated the role of Furin in promoting HSCs mitophagy but leading to inhibition of HSCs persistent activation. Furthermore, we constructed a liver fibrosis mouse model by CCl4-induced method and found that forced expression of Furin caused alleviation of liver fibrosis in CCl4-induced mice. Our findings provide a new clue for understanding liver fibrogenesis and highlight the therapeutic potential of Furin for hepatic fibrosis.

Berberine partially ameliorates cardiolipotoxicity in diabetic cardiomyopathy by modulating SIRT3-mediated lipophagy to remodel lipid droplets homeostasis

BACKGROUND AND PURPOSE

Emerging evidence indicated that the excessive lipid droplets (LDs) accumulation and lipotoxicity play a significant role in the development of diabetic cardiomyopathy (DCM), yet the regulatory mechanisms governing the function of cardiac LDs are still unknown. Lipophagy has been shown to be involved in the maintenance of LDs homeostasis. The objective of this study was to explore the mechanism of lipophagy in cardiomyocytes and investigate whether berberine could mitigate DCM by modulating this pathway.

EXPERIMENTAL APPROACH

Bioinformatics analysis identified disorders of lipid metabolism and autophagy in DCM. To carry out further research, db/db mice were utilized. Furthermore, H9C2 cells treated with palmitic acid were employed as a model to explore the molecular mechanisms involved in myocardial lipotoxicity.

KEY RESULTS

The results showed that lipophagy was impaired in DCM. Mechanistically, sirtuin 3 (SIRT3) was demonstrated to regulate lipophagy in cardiomyocytes. SIRT3 was down-regulated in DCM. Conversely, activation of SIRT3 by the activator nicotinamide riboside (NR) could promote lipophagy to alleviate PA-induced lipotoxicity in H9C2 cells. Moreover, berberine administration markedly mitigated diabetes-induced cardiac dysfunction and hypertrophy in db/db mice, which dependent on SIRT3-mediated lipophagy.

CONCLUSION AND IMPLICATIONS

Collectively, SIRT3 could moderate cardiac lipotoxicity in DCM by promoting lipophagy, suggesting that the regulation of SIRT3-mediated lipophagy may be a promising strategy for treating DCM. The findings indicate that the therapeutic potential of berberine for DCM is associated with lipophagy.

Mitochondrial quality control in cardiomyocytes: safeguarding the heart against disease and ageing

Mitochondria are multifunctional organelles that are important for many different cellular processes, including energy production and biosynthesis of fatty acids, haem and iron-sulfur clusters. Mitochondrial dysfunction leads to a disruption in these processes, the generation of excessive reactive oxygen species, and the activation of inflammatory and cell death pathways. The consequences of mitochondrial dysfunction are particularly harmful in energy-demanding organs such as the heart. Loss of terminally differentiated cardiomyocytes leads to cardiac remodelling and a reduced ability to sustain contraction. Therefore, cardiomyocytes rely on multilayered mitochondrial quality control mechanisms to maintain a healthy population of mitochondria. Mitochondrial chaperones protect against protein misfolding and aggregation, and resident proteases eliminate damaged proteins through proteolysis. Irreparably damaged mitochondria can also be degraded through mitochondrial autophagy (mitophagy) or ejected from cells inside vesicles. The accumulation of dysfunctional mitochondria in cardiomyocytes is a hallmark of ageing and cardiovascular disease. This accumulation is driven by impaired mitochondrial quality control mechanisms and contributes to the development of heart failure. Therefore, there is a strong interest in developing therapies that directly target mitochondrial quality control in cardiomyocytes. In this Review, we discuss the current knowledge of the mechanisms involved in regulating mitochondrial quality in cardiomyocytes, how these pathways are altered with age and in disease, and the therapeutic potential of targeting mitochondrial quality control pathways in cardiovascular disease.

Roles of Autophagy, Mitophagy, and Mitochondria in Left Ventricular Remodeling after Myocardial Infarction

This review examines the mechanisms of left ventricular dysfunction, focusing on the interplay between ventricular remodeling, autophagy, and mitochondrial dysfunction following myocardial infarction. Left ventricular dysfunction directly affects the heart's pumping efficiency and can lead to severe clinical outcomes, including heart failure. After myocardial infarction, the left ventricle may suffer from weakened contractility, diastolic dysfunction, and cardiac remodeling, progressing to heart failure. Thus, this article discusses the pathophysiological processes involved in ventricular remodeling, including the injury and repair of infarcted and non-infarcted myocardia, adaptive changes, and specific changes in left ventricular systolic and diastolic functions. Furthermore, the role of autophagy in maintaining cellular energy homeostasis, clearing dysfunctional mitochondria, and the key role of mitochondrial dysfunction in heart failure is addressed. Finally, this article discusses therapeutic strategies targeting mitochondrial dysfunction and enhancing mitophagy, providing clinicians and researchers with the latest insights and future research directions.

ARHGAP26 deficiency drives the oocyte aneuploidy and early embryonic development failure

Aneuploidy, the presence of a chromosomal anomaly, is a major cause of spontaneous abortions and recurrent pregnancy loss in humans. However, the underlying molecular mechanisms still remain poorly understood. Here, we report that ARHGAP26, a putative tumor suppressor gene, is a newly identified regulator of oocyte quality to maintain mitochondrial integrity and chromosome euploidy, thus ensuring normal embryonic development and fertility. Taking advantage of knockout mouse model, we revealed that genetic ablation of Arhgap26 caused the oocyte death at GV stage due to the mitochondrial dysfunction-induced ROS accumulation. Lack of Arhgap26 also impaired both in vitro and in vivo maturation of survived oocytes which results in maturation arrest and aneuploidy, and consequently leading to early embryonic development defects and subfertility. These observations were further verified by transcriptome analysis. Mechanistically, we discovered that Arhgap26 interacted with Cofilin1 to maintain the mitochondrial integrity by regulating Drp1 dynamics, and restoration of Arhgap26 protein level recovered the quality of Arhgap26-null oocytes. Importantly, we found an ARHGAP26 mutation in a patient with history of recurrent miscarriage by chromosomal microarray analysis. Altogether, our findings uncover a novel function of ARHGAP26 in the oocyte quality control and prevention of aneuploidy and provide a potential treatment strategy for infertile women caused by ARHGAP26 mutation.

Role of Autophagy in Myocardial Remodeling After Myocardial Infarction

ABSTRACT

Autophagy is the process of reusing the body's senescent and damaged cell components, which can be regarded as the cellular circulatory system. There are 3 distinct forms of autophagy: macroautophagy, microautophagy, and chaperone-mediated autophagy. In the heart, autophagy is regulated mainly through mitophagy because of the metabolic changes of cardiomyocytes caused by ischemia and hypoxia. Myocardial remodeling is characterized by gradual heart enlargement, cardiac dysfunction, and extraordinary molecular changes. Cardiac remodeling after myocardial infarction is almost inevitable, which is the leading cause of heart failure. Autophagy has a protective effect on myocardial remodeling improvement. Autophagy can minimize cardiac remodeling by preventing misfolded protein accumulation and oxidative stress. This review summarizes the nestest molecular mechanisms of autophagy and myocardial remodeling, the protective effects, and the new target of autophagy medicine in cardiac remodeling. The future development and challenges of autophagy in heart disease are also summarized.

GRAF1 deficiency leads to defective brown adipose tissue differentiation and thermogenic response

Adipose tissue, which is crucial for the regulation of energy within the body, contains both white and brown adipocytes. White adipose tissue (WAT) primarily stores energy, while brown adipose tissue (BAT) plays a critical role in energy dissipation as heat, offering potential for therapies aimed at enhancing metabolic health. Regulation of the RhoA/ROCK pathway is crucial for appropriate specification, differentiation and maturation of both white and brown adipocytes. However, our knowledge of how this pathway is controlled within specific adipose depots remains unclear, and to date a RhoA regulator that selectively controls adipocyte browning has not been identified. Our study shows that GRAF1, a RhoGAP, is highly expressed in metabolically active tissues, and closely correlates with brown adipocyte differentiation in culture and in vivo. Mice with either global or adipocyte-specific GRAF1 deficiency exhibit impaired BAT maturation and compromised cold-induced thermogenesis. Moreover, defects in differentiation of human GRAF1-deficient brown preadipocytes can be rescued by treatment with a Rho kinase inhibitor. Collectively, these studies indicate that GRAF1 can selectively induce brown adipocyte differentiation and suggest that manipulating GRAF1 activity may hold promise for the future treatment of diseases related to metabolic dysfunction.

The role of rapamycin in the PINK1/Parkin signaling pathway in mitophagy in podocytes

This study aimed to clarify the role of rapamycin in the PINK1/Parkin signaling pathway in mitophagy in podocytes and the role of voltage-dependent anion channel 1 (VDAC1) in the PINK1/Parkin signaling pathway in mouse glomerular podocytes. For this purpose, podocytes were cultured with rapamycin and observed using microscopy. The apoptosis rate of podocytes was detected by flow cytometry. Changes in the mitochondrial membrane potential were measured. The autophagy-related proteins VDAC1, PINK1, Parkin, and LC3 were detected, and mitochondrial autophagosomes were observed via transmission electron microscopy. In the present study, we demonstrated that the number of podocytes treated with rapamycin was significantly reduced. Compared with those in the control group, the apoptosis rate of podocytes and the degree of mitochondrial membrane potential depolarization were significantly higher. We also found the expression levels of VDAC1, PINK1, Parkin, and LC3 were significantly increased. In the rapamycin-treated group, the numbers of swollen mitochondria and mitochondrial autophagosomes were significantly higher. Finally, we showed that rapamycin can upregulate the expression of VDAC1, PINK1, Parkin, and LC3 in glomerular podocytes, which is correlated with mitophagy. VDAC1 is involved in mitophagy and is related to the PINK1/Parkin signaling pathway, serving as an indicator of mitophagy in podocytes.

Developments in the field of intestinal toxicity and signaling pathways associated with rodent exposure to micro(nano)plastics

The broad spread of micro(nano)plastics (MNPs) has garnered significant attention in recent years. MNPs have been detected in numerous human organs, indicating that they may also be hazardous to humans. The toxic effects of MNPs have been demonstrated in marine species and experimental animals. The primary pathway and target organ for MNPs entering the human body is the intestinal system, and increasing research has been done on the harmful effects and subsequent mechanisms of exposure to MNPs. Studies on how MNPs affect gut health in humans are scarce, nevertheless. Since rodents are frequently employed as animal models for human ailments, research on rodents exposed to MNPs can provide a more accurate representation of human circumstances. This study examined the effects of MNPs on intestinal microecology, inflammation, barrier function, and ion transport channels in rodents. It also reviewed the signal pathways involved, such as oxidative stress, nuclear factor (NF)-κB, Toll-like receptor (TLR) 4, inflammatory corpuscles, muscarinic acetylcholine receptors (mAChRs), mitogen-activated protein kinase (MAPK), and cell death. This review will offer a conceptual framework for the management and avoidance of associated illnesses.

ARHGAP26/GRAF1 orchestrates actin remodeling and membrane dynamics to drive mitochondrial clearance and promote fuel flexibility

The serine/threonine kinase, PINK1, and the E3 ubiquitin ligase, PRKN/Parkin facilitate LC3-dependent autophagosomal encasement and lysosomal clearance of dysfunctional mitochondria, and defects in this pathway contribute to the pathogenesis of numerous cardiometabolic and neurological diseases. Although dynamic actin remodeling has recently been shown to play an important role in governing spatiotemporal control of mitophagy, the mechanisms remain unclear. We recently found that the RhoGAP, ARHGAP26/GRAF1 is a PRKN-binding protein that is rapidly recruited to damaged mitochondria where upon phosphorylation by PINK1 it serves to coordinate phagophore capture by regulating mitochondrial-associated actin remodeling and by facilitating PRKN-LC3 interactions. Because ARHGAP26 phosphorylation on PINK1-dependent sites is dysregulated in human heart failure and ARHGAP26 depletion in mouse hearts blunts mitochondrial clearance and attenuates compensatory metabolic adaptations to stress, this enzyme may be a tractable target to treat the many diseases associated with mitochondrial dysfunction.

Decoding the molecular landscape: A novel prognostic signature for uveal melanoma unveiled through programmed cell death-associated genes

Uveal melanoma (UM) is a rare but aggressive malignant ocular tumor with a high metastatic potential and limited therapeutic options, currently lacking accurate prognostic predictors and effective individualized treatment strategies. Public databases were utilized to analyze the prognostic relevance of programmed cell death-related genes (PCDRGs) in UM transcriptomes and survival data. Consensus clustering and Lasso Cox regression analysis were performed for molecular subtyping and risk feature construction. The PCDRG-derived index (PCDI) was evaluated for its association with clinicopathological features, gene expression, drug sensitivity, and immune infiltration. A total of 369 prognostic PCDRGs were identified, which could cluster UM into 2 molecular subtypes with significant differences in prognosis and clinicopathological characteristics. Furthermore, a risk feature PCDI composed of 11 PCDRGs was constructed, capable of indicating prognosis in UM patients. Additionally, PCDI exhibited correlations with the sensitivity to 25 drugs and the infiltration of various immune cells. Enrichment analysis revealed that PCDI was associated with immune regulation-related biological processes and pathways. Finally, a nomogram for prognostic assessment of UM patients was developed based on PCDI and gender, demonstrating excellent performance. This study elucidated the potential value of PCDRGs in prognostic assessment for UM and developed a corresponding risk feature. However, further basic and clinical studies are warranted to validate the functions and mechanisms of PCDRGs in UM.

Dysfunctional mitochondria elicit bioenergetic decline in the aged heart

Aging represents a complex biological progression affecting the entire body, marked by a gradual decline in tissue function, rendering organs more susceptible to stress and diseases. The human heart holds significant importance in this context, as its aging process poses life-threatening risks. It entails macroscopic morphological shifts and biochemical changes that collectively contribute to diminished cardiac function. Among the numerous pivotal factors in aging, mitochondria play a critical role, intersecting with various molecular pathways and housing several aging-related agents. In this comprehensive review, we provide an updated overview of the functional role of mitochondria in cardiac aging.

GRAF1 Acts as a Downstream Mediator of Parkin to Regulate Mitophagy in Cardiomyocytes

Cardiomyocytes rely on proper mitochondrial homeostasis to maintain contractility and achieve optimal cardiac performance. Mitochondrial homeostasis is controlled by mitochondrial fission, fusion, and mitochondrial autophagy (mitophagy). Mitophagy plays a particularly important role in promoting the degradation of dysfunctional mitochondria in terminally differentiated cells. However, the precise mechanisms by which this is achieved in cardiomyocytes remain opaque. Our study identifies GRAF1 as an important mediator in PINK1-Parkin pathway-dependent mitophagy. Depletion of GRAF1 (Arhgap26) in cardiomyocytes results in actin remodeling defects, suboptimal mitochondria clustering, and clearance. Mechanistically, GRAF1 promotes Parkin-LC3 complex formation and directs autophagosomes to damaged mitochondria. Herein, we found that these functions are regulated, at least in part, by the direct binding of GRAF1 to phosphoinositides (PI(3)P, PI(4)P, and PI(5)P) on autophagosomes. In addition, PINK1-dependent phosphorylation of Parkin promotes Parkin-GRAF1-LC3 complex formation, and PINK1-dependent phosphorylation of GRAF1 (on S668 and S671) facilitates the clustering and clearance of mitochondria. Herein, we developed new phosphor-specific antibodies to these sites and showed that these post-translational modifications are differentially modified in human hypertrophic cardiomyopathy and dilated cardiomyopathy. Furthermore, our metabolic studies using serum collected from isoproterenol-treated WT and GRAF1CKO mice revealed defects in mitophagy-dependent cardiomyocyte fuel flexibility that have widespread impacts on systemic metabolism. In summary, our study reveals that GRAF1 co-regulates actin and membrane dynamics to promote cardiomyocyte mitophagy and that dysregulation of GRAF1 post-translational modifications may underlie cardiac disease pathogenesis.