Prohibitin 1 regulates mtDNA release and downstream inflammatory responses.

Exposure of mitochondrial DNA (mtDNA) to the cytosol activates innate immune responses. But the mechanisms by which mtDNA crosses the inner mitochondrial membrane are unknown. Here, we found that the inner mitochondrial membrane protein prohibitin 1 (PHB1) plays a critical role in mtDNA release by regulating permeability across the mitochondrial inner membrane. Loss of PHB1 results in alterations in mitochondrial integrity and function. PHB1-deficient macrophages, serum from myeloid-specific PHB1 KO (Phb1MyeKO) mice, and peripheral blood mononuclear cells from neonatal sepsis patients show increased interleukin-1ß (IL-1ß) levels. PHB1 KO mice are also intolerant of lipopolysaccharide shock. Phb1-depleted macrophages show increased cytoplasmic release of mtDNA and inflammatory responses. This process is suppressed by cyclosporine A and VBIT-4, which inhibit the mitochondrial permeability transition pore (mPTP) and VDAC oligomerization. Inflammatory stresses downregulate PHB1 expression levels in macrophages. Under normal physiological conditions, the inner mitochondrial membrane proteins, AFG3L2 and SPG7, are tethered to PHB1 to inhibit mPTP opening. Downregulation of PHB1 results in enhanced interaction between AFG3L2 and SPG7, mPTP opening, mtDNA release, and downstream inflammatory responses.

Exendin-4 alleviates myocardial ischemia reperfusion injury by enhancing autophagy through promoting nuclear translocation of TFEB.

Ischemia-reperfusion (I/R) injury (IRI) is a common clinical consequence of myocardial infarction. Exendin-4 is a glucagon-like peptide-1 (GLP-1) analog that has been demonstrated to alleviate myocardial IRI. Autophagy, a lysosomal pathway balancing cell survival and cell death, is engaged in myocardial IRI. However, whether exendin-4 exerts a protective effect on myocardial IRI by modulating autophagy remains elusive. Herein, we investigated the effect of exendin-4 on autophagic flux and explored the underlying molecular mechanisms. Our data revealed that the autophagic flux was blocked in the human ventricular cardiomyocyte cell lines (AC16) subjected to oxygen glucose deprivation/reoxygenation (OGD/R) in vitro. Exendin-4 pre-treatment markedly restored the blocked autophagic flux induced by OGD/R through promoting nuclear translocation of TFEB and transcription of genes involving autophagy initiation, the effect of which was reversed by TFEB knockdown. The restoration of autophagic flux contributed to multiple beneficial effects of exendin-4 in cardiomyocytes, including reduction of oxidative stress, preservation of mitochondrial network as well as inhibition of cytochrome c leakage from mitochondrial permeability transition pore (MPTP) and the resulting apoptosis. Moreover, the administration of exendin-4 reduced infarct size and preserved cardiac function through its anti-apoptosis and antioxidative effects in vivo. These results shed some light on understanding the novel mechanism of exendin-4 as a protective agent against myocardial IRI.

FUNDC1 alleviates doxorubicin-induced cardiotoxicity by restoring mitochondrial-endoplasmic reticulum contacts and blocked autophagic flux.

Rationale: Autophagy dysregulation is known to be a mechanism of doxorubicin (DOX)-induced cardiotoxicity (DIC). Mitochondrial-Endoplasmic Reticulum Contacts (MERCs) are where autophagy initiates and autophagosomes form. However, the role of MERCs in autophagy dysregulation in DIC remains elusive. FUNDC1 is a tethering protein of MERCs. We aim to investigate the effect of DOX on MERCs in cardiomyocytes and explore whether it is involved in the dysregulated autophagy in DIC. Methods: We employed confocal microscopy and transmission electron microscopy to assess MERCs structure. Autophagic flux was analyzed using the mCherry-EGFP-LC3B fluorescence assay and western blotting for LC3BII. Mitophagy was studied through the mCherry-EGFP-FIS1 fluorescence assay and colocalization analysis between LC3B and mitochondria. A total dose of 18 mg/kg of doxorubicin was administrated in mice to construct a DIC model in vivo. Additionally, we used adeno-associated virus (AAV) to cardiac-specifically overexpress FUNDC1. Cardiac function and remodeling were evaluated by echocardiography and Masson's trichrome staining, respectively. Results: DOX blocked autophagic flux by inhibiting autophagosome biogenesis, which could be attributed to the downregulation of FUNDC1 and disruption of MERCs structures. FUNDC1 overexpression restored the blocked autophagosome biogenesis by maintaining MERCs structure and facilitating ATG5-ATG12/ATG16L1 complex formation without altering mitophagy. Furthermore, FUNDC1 alleviated DOX-induced oxidative stress and cardiomyocytes deaths in an autophagy-dependent manner. Notably, cardiac-specific overexpression of FUNDC1 protected DOX-treated mice against adverse cardiac remodeling and improved cardiac function. Conclusions: In summary, our study identified that FUNDC1-meditated MERCs exerted a cardioprotective effect against DIC by restoring the blocked autophagosome biogenesis. Importantly, this research reveals a novel role of FUNDC1 in enhancing macroautophagy via restoring MERCs structure and autophagosome biogenesis in the DIC model, beyond its previously known regulatory role as an mitophagy receptor.

TFAM is an autophagy receptor that limits inflammation by binding to cytoplasmic mitochondrial DNA.

When cells are stressed, DNA from energy-producing mitochondria can leak out and drive inflammatory immune responses if not cleared. Cells employ a quality control system called autophagy to specifically degrade damaged components. We discovered that mitochondrial transcription factor A (TFAM)-a protein that binds mitochondrial DNA (mtDNA)-helps to eliminate leaked mtDNA by interacting with the autophagy protein LC3 through an autolysosomal pathway (we term this nucleoid-phagy). TFAM contains a molecular zip code called the LC3 interacting region (LIR) motif that enables this binding. Although mutating TFAM's LIR motif did not affect its normal mitochondrial functions, more mtDNA accumulated in the cell cytoplasm, activating inflammatory signalling pathways. Thus, TFAM mediates autophagic removal of leaked mtDNA to restrict inflammation. Identifying this mechanism advances understanding of how cells exploit autophagy machinery to selectively target and degrade inflammatory mtDNA. These findings could inform research on diseases involving mitochondrial damage and inflammation.

Association between admission-blood-glucose-to-albumin ratio and clinical outcomes in patients with ST-elevation myocardial infarction undergoing percutaneous coronary intervention.

Introduction: It is unclear whether admission-blood-glucose-to-albumin ratio (AAR) predicts adverse clinical outcomes in patients with ST-segment elevation myocardial infarction (STEMI) who are treated with percutaneous coronary intervention (PCI). Here, we performed a observational study to explore the predictive value of AAR on clinical outcomes. Methods: Patients diagnosed with STEMI who underwent PCI between January 2010 and February 2020 were enrolled in the study. The patients were classified into three groups according to AAR tertile. The primary outcome was in-hospital all-cause mortality, and the secondary outcomes were in-hospital major adverse cardiac events (MACEs), as well as all-cause mortality and MACEs during follow-up. Logistic regression, Kaplan-Meier analysis, and Cox proportional hazard regression were the primary analyses used to estimate outcomes. Results: Among the 3,224 enrolled patients, there were 130 cases of in-hospital all-cause mortality (3.9%) and 181 patients (5.4%) experienced MACEs. After adjustment for covariates, multivariate analysis demonstrated that an increase in AAR was associated with an increased risk of in-hospital all-cause mortality [adjusted odds ratio (OR): 2.72, 95% CI: 1.47-5.03, P = 0.001] and MACEs (adjusted OR: 1.91, 95% CI: 1.18-3.10, P = 0.009), as well as long-term all-cause mortality [adjusted hazard ratio (HR): 1.64, 95% CI: 1.19-2.28, P = 0.003] and MACEs (adjusted HR: 1.58, 95% CI: 1.16-2.14, P = 0.003). Receiver operating characteristic (ROC) curve analysis indicated that AAR was an accurate predictor of in-hospital all-cause mortality (AUC = 0.718, 95% CI: 0.675-0.761) and MACEs (AUC = 0.672, 95% CI: 0.631-0.712). Discussion: AAR is a novel and convenient independent predictor of all-cause mortality and MACEs, both in-hospital and long-term, for STEMI patients receiving PCI.