Mitophagy, Mitochondrial Dynamics, and Homeostasis in Cardiovascular Aging

Role of mitochondrial homeostasis in D-galactose-induced cardiovascular ageing from bench to bedside

Ageing is an inevitable phenomenon which affects the cellular to the organism level in the progression of the time. Oxidative stress and inflammation are now widely regarded as the key processes involved in the aging process, which may then cause significant harm to mitochondrial DNA, leading to apoptosis. Normal circulatory function is a significant predictor of disease-free life expectancy. Indeed, disorders affecting the cardiovascular system, which are becoming more common, are the primary cause of worldwide morbidity, disability, and mortality. Cardiovascular aging may precede or possibly underpin overall, age-related health decline. Numerous studies have foundmitochondrial mechanistc approachplays a vital role in the in the onset and development of aging. The D-galactose (D-gal)-induced aging model is well recognized and commonly used in the aging study. In this review we redeposit the association of the previous and current studies on mitochondrial homeostasis and its underlying mechanisms in D-galactose cardiovascular ageing. Further we focus the novel and the treatment strategies to combat the major complication leading to the cardiovascular ageing.

Aflatoxin B1 induces ROS-dependent mitophagy by modulating the PINK1/Parkin pathway in HepG2 cells

Aflatoxin B1 (AFB1) is extremely harmful to both humans and animals. Mitophagy is a selective process of self-elimination and has an important role in controlling mitochondrial quality. The present study aimed to investigate the effect of reactive oxygen species (ROS) accumulation on AFB1-induced mitophagy in HepG2 cells to provide a new perspective from which to design novel therapeutic strategies to treat AFB1 poisoning. ROS release was induced in HepG2 cells with AFB1 (10 μmol/L). Cell autophagy activity, mitochondrial membrane potential (MMP), adenosine triphosphate (ATP) levels, Parkin translocation and both the transcription and expression of mitophagy-related proteins were measured when N-acetyl-L-cysteine (NAC) partially decreased the ROS level, while the knockdown of nuclear factor erythroid 2-related factor 2 (Nrf2) resulted in a large accumulation of ROS. The results reveal that NAC pretreatment ameliorated the decline in both the MMP and the ATP levels while also activating phosphoglycerate mutase 5 (PGAM5)-PTEN-induced kinase 1 (PINK1)/Parkin, while the Nrf2 knockdown group exhibited the opposite trend. These results suggest that AFB1-induced mitophagy in HepG2 cells depends on ROS, and proper ROS activates mitophagy to play a protective role.

Mitophagy in health and disease. Molecular mechanisms, regulatory pathways, and therapeutic implications

Mitophagy, a specialised form of autophagy, selectively targeting damaged or dysfunctional mitochondria, and is crucial for maintaining cellular homeostasis and mitochondrial quality control. Dysregulation of mitophagy contributes to various pathological conditions, including cancer, neurodegenerative and cardiovascular diseases. This review presents a comprehensive analysis of the molecular mechanisms, regulatory pathways, and interplay with other cellular processes governing mitophagy, emphasizing its importance in physiological and pathological contexts. We explore the PINK1/Parkin-mediated and receptor-mediated mitophagy pathways, encompassing BNIP3/NIX, FUNDC1, and Bcl2-L-13. Additionally, we discuss post-translational modifications and cellular signalling pathways modulating mitophagy, as well as the connection between mitophagy and ageing, highlighting the decline in mitophagy efficiency and its impact on age-related pathologies. The review also investigates mitophagy's role in human diseases such as cancer, myocardial ischemia-reperfusion injury, Parkinson's, and Alzheimer's disease. We assess the potential of mitophagy-targeting therapeutic strategies, focusing on the development of dietary therapies, small molecules, drugs, and gene therapy approaches that modulate mitophagy levels and efficiency for treating these diseases and dysfunctions commonly observed in ageing individuals. In summary, this review offers an extensive overview of the molecular mechanisms and regulatory networks involved in mitophagy, its association with autophagy, and implications in human health and disease. By examining the potential of mitophagy-modulating therapies in disease and non-disease settings, we aim to inspire further research to develop innovative treatment strategies for various pathological conditions linked to mitochondrial dysfunction and to ageing.

Neuroprotective effects of apigenin on retinal ganglion cells in ischemia/reperfusion: modulating mitochondrial dynamics in in vivo and in vitro models

BACKGROUND

Retinal ischemia/reperfusion (RIR) is implicated in various forms of optic neuropathies, yet effective treatments are lacking. RIR leads to the death of retinal ganglion cells (RGCs) and subsequent vision loss, posing detrimental effects on both physical and mental health. Apigenin (API), derived from a wide range of sources, has been reported to exert protective effects against ischemia/reperfusion injuries in various organs, such as the brain, kidney, myocardium, and liver. In this study, we investigated the protective effect of API and its underlying mechanisms on RGC degeneration induced by retinal ischemia/reperfusion (RIR).

METHODS

An in vivo model was induced by anterior chamber perfusion following intravitreal injection of API one day prior to the procedure. Meanwhile, an in vitro model was established through 1% oxygen and glucose deprivation. The neuroprotective effects of API were evaluated using H&E staining, spectral-domain optical coherence tomography (SD-OCT), Fluoro-Gold retrograde labeling, and Photopic negative response (PhNR). Furthermore, transmission electron microscopy (TEM) was employed to observe mitochondrial crista morphology and integrity. To elucidate the underlying mechanisms of API, the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, flow cytometry assay, western blot, cell counting kit-8 (CCK-8) assay, lactate dehydrogenase (LDH) assay, JC-1 kit assay, dichlorofluorescein-diacetate (DCFH-DA) assay, as well as TMRE and Mito-tracker staining were conducted.

RESULTS

API treatment protected retinal inner plexiform layer (IPL) and ganglion cell complex (GCC), and improved the function of retinal ganglion cells (RGCs). Additionally, API reduced RGC apoptosis and decreased lactate dehydrogenase (LDH) release by upregulating Bcl-2 and Bcl-xL expression, while downregulating Bax and cleaved caspase-3 expression. Furthermore, API increased mitochondrial membrane potential (MMP) and decreased extracellular reactive oxygen species (ROS) production. These effects were achieved by enhancing mitochondrial function, restoring mitochondrial cristae morphology and integrity, and regulating the expression of OPA1, MFN2, and DRP1, thereby regulating mitochondrial dynamics involving fusion and fission.

CONCLUSION

API protects RGCs against RIR injury by modulating mitochondrial dynamics, promoting mitochondrial fusion and fission.

Mitochondrial Dysfunction: A Roadmap for Understanding and Tackling Cardiovascular Aging

Cardiovascular aging is a progressive remodeling process constituting a variety of cellular and molecular alterations that are closely linked to mitochondrial dysfunction. Therefore, gaining a deeper understanding of the changes in mitochondrial function during cardiovascular aging is crucial for preventing cardiovascular diseases. Cardiac aging is accompanied by fibrosis, cardiomyocyte hypertrophy, metabolic changes, and infiltration of immune cells, collectively contributing to the overall remodeling of the heart. Similarly, during vascular aging, there is a profound remodeling of blood vessel structure. These remodeling present damage to endothelial cells, increased vascular stiffness, impaired formation of new blood vessels (angiogenesis), the development of arteriosclerosis, and chronic vascular inflammation. This review underscores the role of mitochondrial dysfunction in cardiac aging, exploring its impact on fibrosis and myocardial alterations, metabolic remodeling, immune response remodeling, as well as in vascular aging in the heart. Additionally, we emphasize the significance of mitochondria-targeted therapies in preventing cardiovascular diseases in the elderly.

Mitophagy in neurodegenerative disease pathogenesis

Mitochondria are critical cellular energy resources and are central to the life of the neuron. Mitophagy selectively clears damaged or dysfunctional mitochondria through autophagic machinery to maintain mitochondrial quality control and homeostasis. Mature neurons are postmitotic and consume substantial energy, thus require highly efficient mitophagy pathways to turn over damaged or dysfunctional mitochondria. Recent evidence indicates that mitophagy is pivotal to the pathogenesis of neurological diseases. However, more work is needed to study mitophagy pathway components as potential therapeutic targets. In this review, we briefly discuss the characteristics of nonselective autophagy and selective autophagy, including ERphagy, aggrephagy, and mitophagy. We then introduce the mechanisms of Parkin-dependent and Parkin-independent mitophagy pathways under physiological conditions. Next, we summarize the diverse repertoire of mitochondrial membrane receptors and phospholipids that mediate mitophagy. Importantly, we review the critical role of mitophagy in the pathogenesis of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Last, we discuss recent studies considering mitophagy as a potential therapeutic target for treating neurodegenerative diseases. Together, our review may provide novel views to better understand the roles of mitophagy in neurodegenerative disease pathogenesis.

Nicotinamide Mononucleotide and Nicotinamide Riboside Reverse Ovarian Aging in Rats Via Rebalancing Mitochondrial Fission and Fusion Mechanisms

PURPOSE

This study examined the effects of nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) on folliculogenesis and mitochondrial dynamics (fission and fusion mechanisms) in ovaries of middle-aged female rats.

METHODS

Experimental groups were young, middle-aged (control), middle-aged + NMN and middle-aged + NR. NMN was administered at a concentration of 500 mg/kg intraperitoneally but NR at a concentration of 200 mg/kg by gavage. Follicle stimulating hormone (FSH) and luteinizing hormone (LH) levels were analyzed by ELISA. Hematoxylin-eosin staining sections were used for histopathological examination and follicles-counting. Expression levels of mitochondrial fission (Drp1, Mff and Fis1) and fusion (Mfn1, Mfn2, Opa1, Fam73a and Fam73b) genes as well as Sirt1 gene were analyzed by RT-PCR. Expression levels of fission-related proteins (DRP1, MFF, FIS1 and SIRT1) were analyzed by Western Blot.

RESULTS

Higher ovarian index, more corpus luteum and antral follicles were detected in NMN and NR groups compared to the control. NMN or NR could rebalance LH/FSH ratio. The control group was determined to possess higher expression levels of fission genes and lower expression levels of fusion genes when compared the young group. In comparison with the control group, both NMN and NR group were found to exhibit less mitochondrial fission but more mitochondrial fussion. Higher gene and protein levels for Sirt1 were measured in NMN and NR groups compared to the control group.

CONCLUSION

This study reveals that NMN alone or NR alone can rebalance mitochondrial dynamics by decreasing excessive fission in middle-aged rat ovaries, thus alleviating mitochondrial stress and correcting aging-induced folliculogenesis abnormalities.

DsbA-L ameliorates renal aging and renal fibrosis by maintaining mitochondrial homeostasis

Renal fibrosis is the final pathological change in renal disease, and aging is closely related to renal fibrosis. Mitochondrial dysfunction has been reported to play an important role in aging, but the exact mechanism remains unclear. Disulfide-bond A oxidoreductase-like protein (DsbA-L) is mainly located in mitochondria and plays an important role in regulating mitochondrial function and endoplasmic reticulum (ER) stress. However, the role of DsbA-L in renal aging has not been reported. In this study, we showed a reduction in DsbA-L expression, the disruption of mitochondrial function and an increase in fibrosis in the kidneys of 12- and 24-month-old mice compared to young mice. Furthermore, the deterioration of mitochondrial dysfunction and fibrosis were observed in DsbA-L-/- mice with D-gal-induced accelerated aging. Transcriptome analysis revealed a decrease in Flt4 expression and inhibition of the PI3K-AKT signaling pathway in DsbA-L-/- mice compared to control mice. Accelerated renal aging could be alleviated by an AKT agonist (SC79) or a mitochondrial protector (MitoQ) in mice with D-gal-induced aging. In vitro, overexpression of DsbA-L in HK-2 cells restored the expression of Flt4, AKT pathway factors, SP1 and PGC-1α and alleviated mitochondrial damage and cell senescence. These beneficial effects were partially blocked by inhibiting Flt4. Finally, activating the AKT pathway or improving mitochondrial function with chemical reagents could alleviate cell senescence. Our results indicate that the DsbA-L/AKT/PGC-1α signaling pathway could be a therapeutic target for age-related renal fibrosis and is associated with mitochondrial dysfunction.

Moderate replacement of fish oil with palmitic acid-stimulated mitochondrial fusion promotes β-oxidation by Mfn2 interacting with Cpt1α via its GTPase-domain

The mitochondrial matrix serves as the principal locale for the process of fatty acids (FAs) β-oxidation. Preserving the integrity and homeostasis of mitochondria, which is accomplished through ongoing fusion and fission events, is of paramount importance for the effective execution of FAs β-oxidation. There has been no investigation to date into whether and how mitochondrial fusion directly enhances FAs β-oxidation. The underlying mechanism of a balanced FAs ratio favoring hepatic lipid homeostasis remains largely unclear. To address such gaps, the present study was conducted to investigate the mechanism through which a balanced dietary FAs ratio enhances hepatic FAs β-oxidation. The investigation specifically focused on the involvement of Mfn2-mediated mitochondrial fusion in the regulation of Cpt1α in this process. In the present study, the yellow catfish (Pelteobagrus fulvidraco), recognized as a model organism for lipid metabolism, were subjected to eight weeks of in vivo feeding with six distinct diets featuring varying FAs ratios. Additionally, in vitro experiments were conducted to inhibit Mfn2-mediated mitochondrial fusion in isolated hepatocytes, achieved through the transfection of hepatocytes with si-mfn2. Further, deletion mutants for both Mfn2 and Cpt1α were constructed to elucidate the critical regions responsible for the interactions between these two proteins within the system. The key findings were: (1) Substituting palmitic acid (PA) for fish oil (FO) proved to be enhanced in reducing hepatic lipid accumulation. This beneficial effect was primarily attributed to the activation of mitochondrial FAs β-oxidation; (2) The balanced replacement of PA stimulated Mfn2-mediated mitochondrial fusion by diminishing Mfn2 ubiquitination, thereby enhancing its protein retention within the mitochondria; (3) Mfn2-mediated mitochondrial fusion promoted FAs β-oxidation through direct interaction between Mfn2 and Cpt1α via its GTPase-domains, which is essential for the maintenance of Cpt1 activity. Notably, the present research results unveil a previously undisclosed mechanism wherein Mfn2-mediated mitochondrial fusion promotes FAs β-oxidation by directly augmenting the capacity for FA transport into mitochondria (MT), in addition to expanding the mitochondrial matrix. This underscores the pivotal role of mitochondrial fusion in preserving hepatic lipid homeostasis. The present results further confirm that these mechanisms are evolutionarily conserved, extending their relevance from fish to mammals.

Silver nanoparticles induced synaptic degeneration via Ca2+/CaMKII signal and Drp1-dependent mitochondrial disorder in HT22 cells

Silver nanoparticles (AgNPs) have been widely used in biomedicine and cosmetics, increasing their potential risks in neurotoxicity. But the involved molecular mechanism remains unclear. This study aims to explore molecular events related to AgNPs-induced neuronal damage by RNA-seq, and elucidate the role of Ca2+/CaMKII signal and Drp1-dependent mitochondrial disorder in HT22 cells synaptic degeneration induced by AgNPs. This study found that cell viabilities were decreased by AgNPs in a dose/time-dependent manner. AgNPs also increased protein expression of PINK1, Parkin, synaptophysin, and inhibited PGC-1α, MAP2 and APP protein expression, indicating AgNPs-induced synaptic degeneration involved in disturbance of mitophagy and mitochondrial biogenesis in HT22 cells. Moreover, inhibition of AgNPs-induced Ca2+/CaMKII activation and Drp1/ROS rescued mitophagy disturbance and synaptic degeneration in HT22 cells by reserving aforementioned protein express changes except for PGC-1α and APP protein. Thus, AgNPs-induced synaptic degeneration was mediated by Ca2+/CaMKII signal and Drp1-dependent mitochondrial disorder in HT22 cells, and mitophagy is the sensitive to the mechanism. Our study will provide in-depth molecular mechanism data for neurotoxic evaluation and biomedical application of AgNPs.

Cardioprotective effect of naringin against the ischemia/reperfusion injury of aged rats

Aging is known as a main risk factor in the development of cardiovascular diseases. Naringin (NRG) is a flavonoid compound derived from citrus fruits. It possesses a wide spectrum of pharmacological properties, including antioxidant anti-inflammatory, and cardioprotective. This investigation aimed to assess the cardioprotective effect of NRG against the ischemia/reperfusion (I/R) injury in aged rats. In this study, D-galactose (D-GAL) at the dose of 150 mg/kg/day for 8 weeks was used to induce aging in rats. Rats were orally gavaged with NRG (40 or 100 mg/kg/day), in co-treatment with D-GAL, for 8 weeks. The Langendorff isolated heart was used to evaluate the effect of NRG on I/R injury in aged rats. NRG treatment diminished myocardial hypertrophy and maximum contracture level in aged animals. During the pre-ischemic phase, reduced heart rate was normalized by NRG. The effects of D-GAL on the left ventricular end diastolic pressure (LVDP), the rate pressure product (RPP), and the minimum and maximum rate of left ventricular pressure (±dp/dt) improved by NRG treatment in the perfusion period. NRG also enhanced post-ischemic recovery of cardiac functional parameters (± dp/dt, and RPP) in isolated hearts. An increase in serum levels of the lactate dehydrogenase (LDH), the creatine kinase-MB (CK-MB), and the tumor necrosis factor-alpha (TNF-α) were reversed by NRG in aged rats. It also normalized the D-GAL-decreased the superoxide dismutase (SOD) activity in the heart tissue. NRG treatment alleviated cardiac injury in aged hearts under conditions of I/R. NRG may improve aging-induced cardiac dysfunction through anti-oxidative and anti-inflammatory mechanisms.

Cardiomyocyte-specific deletion of endothelin receptor A (ETA) obliterates cardiac aging through regulation of mitophagy and ferroptosis

Advanced aging evokes unfavorable changes in the heart including cardiac remodeling and contractile dysfunction although the underlying mechanism remains elusive. This study was conducted to evaluate the role of endothelin-1 (ET-1) in the pathogenesis of cardiac aging and mechanism involved. Echocardiographic and cardiomyocyte mechanical properties were determined in young (5-6 mo) and aged (26-28 mo) wild-type (WT) and cardiomyocyte-specific ETA receptor knockout (ETAKO) mice. GSEA enrichment identified differentially expressed genes associated with mitochondrial respiration, mitochondrial protein processing and mitochondrial depolarization in cardiac aging. Aging elevated plasma levels of ET-1, Ang II and suppressed serum Fe2+, evoked cardiac remodeling (hypertrophy and interstitial fibrosis), contractile defects (fractional shortening, ejection fraction, cardiomyocyte peak shortening, maximal velocity of shortening/relengthening and prolonged relengthening) and intracellular Ca2+ mishandling (dampened intracellular Ca2+ release and prolonged decay), the effects with the exception of plasma AngII, ET-1 and Fe2+ were mitigated by ETAKO. Advanced age facilitated O2- production, carbonyl protein damage, cardiac hypertrophy (GATA4, ANP, NFATc3), ER stress, ferroptosis, compromised autophagy (LC3B, Beclin-1, Atg7, Atg5 and p62) and mitophagy (parkin and FUNDC1), and deranged intracellular Ca2+ proteins (SERCA2a and phospholamban), the effects of which were reversed by ETA ablation. ET-1 provoked ferroptosis in vitro, the response was nullified by the ETA receptor antagonist BQ123 and mitophagy inducer CsA. ETA but not ETB receptor antagonism reconciled cardiac aging, which was abrogated by inhibition of mitophagy and ferroptosis. These findings collectively denote promises of targeting ETA, mitophagy and ferroptosis in the management of aging-associated cardiac remodeling and contractile defect.

SIRT3 suppression resulting from the enhanced β-catenin signaling drives glycolysis and promotes hypoxia-induced cell growth in hepatocellular carcinoma cells

The precise mechanisms underlying the inhibitory effects of SIRT3, a mitochondrial sirtuin protein, on hepatocellular carcinoma (HCC) development, as well as its impact on mitochondrial respiration, remain poorly understood. We assessed sirtuins 3 (SIRT3) levels in HCC tissues and Huh7 cells cultured under hypoxic condition. We investigated the effects of SIRT3 on cell proliferation, glycolytic metabolism, mitochondrial respiration, mitophagy, and mitochondrial biogenesis in Huh7 cells. Besides, we explored the potential mechanisms regulating SIRT3 expression in hypoxically cultured Huh7 cells. Gradual reduction in SIRT3 expressions were observed in both adjacent tumor tissues and tumor tissues. Similarly, SIRT3 expressions were diminished in Huh7 cells cultured under hypoxic condition. Forced expression of SIRT3 attenuated the growth of hypoxically cultured Huh7 cells. SIRT3 overexpression led to a decrease in extracellular acidification rate while increasing oxygen consumption rate. SIRT3 downregulated the levels of hexokinase 2 and pyruvate kinase M2. Moreover, SIRT3 enhanced mitophagy signaling, as indicated by mtKeima, and upregulated key proteins involved in various mitophagic pathways while reducing intracellular reactive oxygen species levels. Furthermore, SIRT3 increased proxisome proliferator-activated receptor-gamma coactivator 1α levels and the amount of mitochondrial DNA in Huh7 cells. Notably, β-catenin expressions were elevated in Huh7 cells cultured under hypoxic condition. Antagonists and agonists of β-catenin respectively upregulated and downregulated SIRT3 expressions in hypoxically cultured Huh7 cells. The modulationsof glycolysis and mitochondrial respiration represent the primary mechanism through which SIRT3, suppressed by β-catenin, inhibits HCC cell proliferation.

FOXO1 reduces STAT3 activation and causes impaired mitochondrial quality control in diabetic cardiomyopathy

AIMS

To investigate the role of FOXO1 in STAT3 activation and mitochondrial quality control in the diabetic heart.

METHODS

Type 1 diabetes mellitus (T1DM) was induced in rats by a single intraperitoneal injection of 60 mg · kg-1 streptozotocin (STZ), while type 2 diabetes mellitus (T2DM) was induced in rats with a high-fat diet through intraperitoneal injection of 35 mg · kg-1 STZ. Primary neonatal mouse cardiomyocytes and H9c2 cells were exposed to low glucose (5.5 mM) or high glucose (HG; 30 mM) with or without treatment with the FOXO1 inhibitor AS1842856 (1 μM) for 24 hours. In addition, the diabetic db/db mice (aged 8 weeks) and sex- and age-matched non-diabetic db/+ mice were treated with vehicle or AS1842856 by oral gavage for 15 days at a dose of 5 mg · kg-1  · d-1 .

RESULTS

Rats with T1DM or T2DM had excessive cardiac FOXO1 activation, accompanied by decreased STAT3 activation. Immunofluorescence and immunoprecipitation analysis showed colocalization and association of FOXO1 and STAT3 under basal conditions in isolated cardiomyocytes. Selective inhibition of FOXO1 activation by AS1842856 or FOXO1 siRNA transfection improved STAT3 activation, mitophagy and mitochondrial fusion, and decreased mitochondrial fission in isolated cardiomyocytes exposed to HG. Transfection with STAT3 siRNA further reduced mitophagy, mitochondrial fusion and increased mitochondrial fission in HG-treated cardiomyocytes. AS1842856 alleviated cardiac dysfunction, pathological damage and improved STAT3 activation, mitophagy and mitochondrial dynamics in diabetic db/db mice. Additionally, AS1842856 improved mitochondrial function indicated by increased mitochondrial membrane potential and adenosine triphosphate production and decreased mitochondrial reactive oxygen species production in isolated cardiomyocytes exposed to HG.

CONCLUSIONS

Excessive FOXO1 activation during diabetes reduces STAT3 activation, with subsequent impairment of mitochondrial quality, ultimately promoting the development of diabetic cardiomyopathy.

Cardiovascular diseases crossroads: cGAS-STING signaling and disease progression

It is now widely accepted that inflammation is critical in cardiovascular diseases (CVD). Here, studies are being conducted on how cyclic GMP-AMP synthase (cGAS), a component of innate immunity's DNA-sensing machinery, communicates with the STING receptor, which is involved in activating the immune system's antiviral response. Significantly, a growing body of research in recent years highlights the strong activation of the cGAS-STING signalling pathways in several cardiovascular diseases, such as myocardial infarction, heart failure, and myocarditis. This developing collection of research emphasises these pathways' crucial role in initiating and advancing cardiovascular disease. In this extensive narrative, we explore the role of the cGAS-STING pathway in the development of CVD. We elaborate on the basic mechanisms involved in the onset and progression of CVD. This review explores the most recent developments in the recognition and characterization of cGAS-STING pathway. Additionally, it considers the field's future prospects while examining how cGAS-STING pathway might be altered and its clinical applications for cardiovascular diseases.

Homocysteine and mitochondrial quality control in diabetic retinopathy

BACKGROUND

Diabetic retinopathy is a progressive disease, and one of the key metabolic abnormalities in the pathogenesis of diabetic retinopathy, mitochondrial damage, is also influenced by the duration of hyperglycemia. Mitochondrial quality control involves a coordination of mitochondrial dynamics, biogenesis and removal of the damaged mitochondria. In diabetes, these processes are impaired, and the damaged mitochondria continue to produce free radicals. Diabetic patients also have high homocysteine and reduced levels of hydrogen sulfide, and hyperhomocysteinemia is shown to exacerbate diabetes-induced mitochondrial damage and worsen their dynamics. This study aims to investigate the temporal relationship between hyperhomocysteinemia and retinal mitochondrial quality control in diabetic retinopathy.

METHODS

Human retinal endothelial cells incubated in 20 mM D-glucose for 24 to 96 h, in the absence or presence of 100 µM homocysteine, with/without a hydrogen sulfide donor GYY4137, were analyzed for mitochondrial ROS (MitoSox fluorescence), DNA damage (transcripts of mtDNA-encoded ND6 and CytB), copy numbers, oxygen consumption rate (Seahorse XF analyzer) and mitophagy (mitophagosomes immunofluorescence labeling and flow cytometry). Results were confirmed in the retina from mice genetically manipulated for hyperhomocysteinemia (cystathionine β-synthase deficient mice, Cbs+/-), streptozotocin-induced diabetic for 8 to 24 weeks. At 24 weeks of diabetes, vascular health was evaluated by counting acellular capillaries in the trypsin digested retinal vasculature and by fluorescein angiography.

RESULTS

Homocysteine, in high glucose medium, exacerbated mitochondrial ROS production, mtDNA damage and impaired mitochondrial respiration within 24 h, and slowed down/worsened mitochondrial biogenesis and mitophagy, as compared to 48 to 96 h in high glucose alone. GYY4137 supplementation ameliorated homocysteine + high glucose-induced mitochondrial damage and impairment in biogenesis and mitophagy. Similar results were obtained from Cbs+/- mice-mitochondrial ROS, mtDNA damage and decline in biogenesis and mitophagy were observed within eight weeks of diabetes vs. 16 to 24 weeks of diabetes in Cbs+/+ mice, and at 24 weeks of diabetes, Cbs+/- mice had significantly higher acellular capillaries and vascular leakage.

CONCLUSIONS

Hyperhomocysteinemia, in a hyperglycemic environment, overwhelms the mitochondria, accelerating and exacerbating their dysfunction, and also delays/worsens their removal, augmenting the development of diabetic retinopathy. Thus, our results strengthen the importance of maintaining homocysteine-hydrogen sulfide balance during the early stages of diabetes for a patient to prevent/retard vision loss.

Mitophagy in hypertension-mediated organ damage

Hypertension constitutes a pervasive chronic ailment on a global scale, frequently inflicting damage upon vital organs, such as the heart, blood vessels, kidneys, brain, and others. And this is a complex clinical dilemma that requires immediate attention. The mitochondria assume a crucial function in the generation of energy, and it is of utmost importance to eliminate any malfunctioning or surplus mitochondria to uphold intracellular homeostasis. Mitophagy is considered a classic example of selective autophagy, an important component of mitochondrial quality control, and is closely associated with many physiological and pathological processes. The ubiquitin-dependent pathway, facilitated by PINK1/Parkin, along with the ubiquitin-independent pathway, orchestrated by receptor proteins such as BNIP3, NIX, and FUNDC1, represent the extensively investigated mechanisms underlying mitophagy. In recent years, research has increasingly shown that mitophagy plays an important role in organ damage associated with hypertension. Exploring the molecular mechanisms of mitophagy in hypertension-mediated organ damage could represent a critical avenue for future research in the development of innovative therapeutic modalities. Therefore, this article provides a comprehensive review of the impact of mitophagy on organ damage due to hypertension.

Trafficking and effect of released DNA on cGAS-STING signaling pathway and cardiovascular disease

Evidence from clinical research and animal studies indicates that inflammation is an important factor in the occurrence and development of cardiovascular disease (CVD). Emerging evidence shows that nucleic acids serve as crucial pathogen-associated molecular patterns (PAMPs) or non-infectious damage-associated molecular patterns (DAMPs), are released and then recognized by pattern recognition receptors (PRRs), which activates immunological signaling pathways for host defense. Mechanistically, the released nucleic acids activate cyclic GMP-AMP synthase (cGAS) and its downstream receptor stimulator of interferon genes (STING) to promote type I interferons (IFNs) production, which play an important regulatory function during the initiation of an innate immune response to various diseases, including CVD. This pathway represents an essential defense regulatory mechanism in an organism's innate immune system. In this review, we outline the overall profile of cGAS-STING signaling, summarize the latest findings on nucleic acid release and trafficking, and discuss their potential role in CVD. This review also sheds light on potential directions for future investigations on CVD.

The role of inflammation and antioxidant defenses in the cardiotoxicity of doxorubicin in elderly CD-1 male mice

Doxorubicin (DOX) is a potent chemotherapeutic agent used against several cancer types. However, due to its cardiotoxic adverse effects, the use of this drug may be also life-threatening. Although most cancer patients are elderly, they are poorly represented and evaluated in pre-clinical and clinical studies. Considering this, the present work aims to evaluate inflammation and oxidative stress as the main mechanisms of DOX-induced cardiotoxicity, in an innovative approach using an experimental model constituted of elderly animals treated with a clinically relevant human cumulative dose of DOX. Elderly (18-20 months) CD-1 male mice received biweekly DOX administrations, for 3 weeks, to reach a cumulative dose of 9.0 mg/kg. One week (1W) or two months (2 M) after the last DOX administration, the heart was collected to determine both drug's short and longer cardiac adverse effects. The obtained results showed that DOX causes cardiac histological damage and fibrosis at both time points. In the 1W-DOX group, the number of nuclear factor kappa B (NF-κB) p65 immunopositive cells increased and a trend toward increased NF-κB p65 expression was seen. An increase of inducible nitric oxide synthase (iNOS) and interleukin (IL)-33 and a trend toward increased IL-6 and B-cell lymphoma-2-associated X (Bax) expression were seen after DOX. In the same group, a decrease in IL-1β, p62, and microtubule-associated protein 1A/1B-light chain 3 (LC3)-I, p38 mitogen-activated protein kinase (MAPK) expression was observed. Contrariwise, the animals sacrificed 2 M after DOX showed a significant increase in glutathione peroxidase 1 and Bax expression with persistent cardiac damage and fibrosis, while carbonylated proteins, erythroid-2-related factor 2 (Nrf2), NF-κB p65, myeloperoxidase, LC3-I, and LC3-II expression decreased. In conclusion, our study demonstrated that in an elderly mouse population, DOX induces cardiac inflammation, autophagy, and apoptosis in the heart in the short term. When kept for a longer period, oxidative-stress-linked pathways remained altered, as well as autophagy markers and tissue damage after DOX treatment, emphasizing the need for continuous post-treatment cardiac monitoring.

Targeting gut microbiota in aging-related cardiovascular dysfunction: focus on the mechanisms

The global population is aging and age-related cardiovascular disease is increasing. Even after controlling for cardiovascular risk factors, readmission and mortality rates remain high. In recent years, more and more in-depth studies have found that the composition of the gut microbiota and its metabolites, such as trimethylamine N-oxide (TMAO), bile acids (BAs), and short-chain fatty acids (SCFAs), affect the occurrence and development of age-related cardiovascular diseases through a variety of molecular pathways, providing a new target for therapy. In this review, we discuss the relationship between the gut microbiota and age-related cardiovascular diseases, and propose that the gut microbiota could be a new therapeutic target for preventing and treating cardiovascular diseases.

Folic Acid Protects against Ethanol-Induced Hepatic Mitophagy Imbalance by ROS Scavenging and Attenuating the Elevated Hcy Levels

Ample evidence indicates that ethanol-induced oxidative stress and mitochondrial dysfunction are central to the pathogenesis of alcoholic liver disease (ALD). As an adaptive quality control mechanism, mitophagy removes dysfunctional mitochondria to avert hepatic lesions in ALD. Folic acid exhibits potential radical scavenging properties and has been proven to ameliorate mitochondrial disorder in oxidative stress-related diseases. In this study, we aimed to uncover the mitophagy regulatory effects of folic acid in a 10w alcohol C57BL/6J mice feeding model (56% v/v) and L02 cells model cultured with ethanol (2.5% v/v). The results showed that folic acid alleviates ethanol-induced liver injury, decreasing oxidative stress and restoring liver enzyme. Furthermore, folic acid improved the mitochondrial function and inhibited ethanol-activated mitophagy through decreasing PINK1-Parkin and Drp1 expression, which inhibited the release of mitochondrial cytochrome C to the cytoplasm, preventing hepatocyte apoptosis. Intriguingly, folic acid attenuates the elevated hepatic homocysteine (Hcy) level. Additionally, the pretreatment of L02 cells with folic acid also ameliorated Hcy-induced oxidative damage, mitochondrial fission, and mitophagy. In summary, these results suggest that folic acid has beneficial effects in mitophagy remodeling by ROS scavenging and facilitating Hcy metabolism and could be developed as a potential therapeutic agent against ALD.

Protective effects of catalpol on cardio-cerebrovascular diseases: A comprehensive review

Catalpol, an iridoid glucoside isolated from Rehmannia glutinosa, has gained attention due to its potential use in treating cardio-cerebrovascular diseases (CVDs). This extensive review delves into recent studies on catalpol's protective properties in relation to various CVDs, such as atherosclerosis, myocardial ischemia, infarction, cardiac hypertrophy, and heart failure. The review also explores the compound's anti-oxidant, anti-inflammatory, and anti-apoptotic characteristics, emphasizing the role of vital signaling pathways, including PGC-1α/TERT, PI3K/Akt, AMPK, Nrf2/HO-1, estrogen receptor (ER), Nox4/NF-κB, and GRP78/PERK. The article discusses emerging findings on catalpol's ability to alleviate diabetic cardiovascular complications, thrombosis, and other cardiovascular-related conditions. Although clinical studies specifically addressing catalpol's impact on CVDs are scarce, the compound's established safety and well-tolerated nature suggest that it could be a valuable treatment alternative for CVD patients. Further investigation into catalpol and related iridoid derivatives may unveil new opportunities for devising natural and efficacious CVD therapies.

Aerobic exercise enhances mitochondrial homeostasis to counteract D-galactose-induced sarcopenia in zebrafish

Sarcopenia is a common skeletal muscle degenerative disease characterized by decreased skeletal muscle mass and mitochondrial dysfunction that involves microRNAs (miR) as regulatory factors in various pathways. Exercise reduces age-related oxidative damage and chronic inflammation and increases autophagy, among others. Moreover, whether aerobic exercise can regulate mitochondrial homeostasis by modulating the miR-128/insulin-like growth factor-1 (IGF-1) signaling pathway and can improve sarcopenia requires further investigation. Interestingly, zebrafish have been used as a model for aging research for over a decade due to their many outstanding advantages. Therefore, we established a model of zebrafish sarcopenia using d-galactose immersion and observed substantial changes, including reduced skeletal muscle cross-sectional area, increased tissue fibrosis, decreased motility, increased skeletal muscle reactive oxygen species, and notable alterations in mitochondrial morphology and function. We found that miR-128 expression was considerably upregulated, where as Igf1 and peroxisome proliferator-activated receptor gamma coactivator 1-alpha were significantly downregulated; moreover, mitochondrial homeostasis was reduced. Four weeks of aerobic exercise delayed sarcopenia progression and prevented the disruption of mitochondrial function and homeostasis. The genes related to atrophy and miR-128 were downregulated, Igf1 expression was considerably upregulated, and the phosphorylation levels of Pi3k, Akt, and Foxo3a were upregulated. Furthermore, mitochondrial respiration and homeostasis were enhanced. In conclusion, aerobic exercise improved skeletal muscle quality and function via the miR-128/IGF-1 signaling pathway, consequently ameliorating mitochondrial homeostasis in aging skeletal muscle.

Mitochondrial heterogeneity in diseases

As key organelles involved in cellular metabolism, mitochondria frequently undergo adaptive changes in morphology, components and functions in response to various environmental stresses and cellular demands. Previous studies of mitochondria research have gradually evolved, from focusing on morphological change analysis to systematic multiomics, thereby revealing the mitochondrial variation between cells or within the mitochondrial population within a single cell. The phenomenon of mitochondrial variation features is defined as mitochondrial heterogeneity. Moreover, mitochondrial heterogeneity has been reported to influence a variety of physiological processes, including tissue homeostasis, tissue repair, immunoregulation, and tumor progression. Here, we comprehensively review the mitochondrial heterogeneity in different tissues under pathological states, involving variant features of mitochondrial DNA, RNA, protein and lipid components. Then, the mechanisms that contribute to mitochondrial heterogeneity are also summarized, such as the mutation of the mitochondrial genome and the import of mitochondrial proteins that result in the heterogeneity of mitochondrial DNA and protein components. Additionally, multiple perspectives are investigated to better comprehend the mysteries of mitochondrial heterogeneity between cells. Finally, we summarize the prospective mitochondrial heterogeneity-targeting therapies in terms of alleviating mitochondrial oxidative damage, reducing mitochondrial carbon stress and enhancing mitochondrial biogenesis to relieve various pathological conditions. The possibility of recent technological advances in targeted mitochondrial gene editing is also discussed.

The additive effects of nicotinamide mononucleotide and melatonin on mitochondrial biogenesis and fission/fusion, autophagy, and microRNA-499 in the aged rat heart with reperfusion injury

The prognosis of myocardial ischemia/reperfusion (I/R) injury is poor in elderly patients. Aging increases the susceptibility of the heart to cell death from I/R injury and prevents the optimal effectiveness of cardioprotective modalities. Since the interaction of aging with cardioprotection is multifactorial, combination therapy may overcome the above-mentioned burden through correcting various components of the injury. Here, we explored the effects of nicotinamide mononucleotide (NMN)/melatonin combination therapy on mitochondrial biogenesis and fission/fusion, autophagy, and microRNA-499 in the aged rat heart with reperfusion injury. Ex vivo model of myocardial I/R injury was established by coronary occlusion and re-opening in 30 aged male Wistar rats (400-450 g, 22-24 months old). NMN (100 mg/kg/48 h, intraperitoneally) was administered over 28 days before I/R, and melatonin (50 µM) was added to the perfusion solution at early reperfusion. CK-MB release and expression of mitochondrial biogenesis genes and proteins, mitochondrial fission/fusion proteins, autophagy genes, and microRNA-499 were assessed. NMN/melatonin combination therapy concomitantly decreased CK-MB release in aged reperfused hearts (P < .001). It also upregulated SIRT1/PGC-1α/Nrf1/TFAM profiles at both gene and protein levels, Mfn2 protein, and microRNA-499 expression, and downregulated Drp1 protein and Beclin1, LC3, and p62 genes (P < .05 to P < .001). The effect of combination therapy was greater than individual ones. Co-application of NMN/melatonin within the setting of I/R injury in the aged rat heart induced noticeable cardioprotection through modulation of a coordinated network including microRNA-499 expression along with mitochondrial biogenesis associated with SIRT1/PGC-1α/Nrf1/TFAM profiles, mitochondrial fission/fusion, and autophagy, therefore, appears to prevent the burden of myocardial I/R injury in elderly patients.

Mitochondrial dysfunction in heart diseases: Potential therapeutic effects of Panax ginseng

Heart diseases have a high incidence and mortality rate, and seriously affect people's quality of life. Mitochondria provide energy for the heart to function properly. The process of various heart diseases is closely related to mitochondrial dysfunction. Panax ginseng (P. ginseng), as a traditional Chinese medicine, is widely used to treat various cardiovascular diseases. Many studies have confirmed that P. ginseng and ginsenosides can regulate and improve mitochondrial dysfunction. Therefore, the role of mitochondria in various heart diseases and the protective effect of P. ginseng on heart diseases by regulating mitochondrial function were reviewed in this paper, aiming to gain new understanding of the mechanisms, and promote the clinical application of P. ginseng.

Cardiovascular disease treatment using traditional Chinese medicine：Mitochondria as the Achilles' heel

Cardiovascular disease (CVD), involving the pathological alteration of the heart or blood vessels, is one of the main causes of disability and death worldwide, with an estimated 18.6 million deaths per year. CVDs are caused by a variety of risk factors, including inflammation, hyperglycemia, hyperlipidemia, and increased oxidative stress. Mitochondria, the hub of ATP production and the main generator of reactive oxygen species (ROS), are linked to multiple cellular signaling pathways that regulate the progression of CVD and therefore are recognized as an essential target for CVD management. Initial treatment of CVD generally focuses on diet and lifestyle interventions; proper drugs or surgery can prolong or save the patient's life. Traditional Chinese medicine (TCM), a holistic medical care system with an over 2500-year history, has been proven to be efficient in curing CVD and other illnesses, with a strengthening effect on the body. However, the mechanisms underlying TCM alleviation of CVD remain elusive. Recent studies have recognized that TCM can alleviate cardiovascular disease by manipulating the quality and function of mitochondria. This review systematically summarizes the association of mitochondria with cardiovascular risk factors, and the relationships between mitochondrial dysfunction and CVD progression. We will investigate the research progress of managing cardiovascular disease by TCM and cover widely used TCMs that target mitochondria for the treatment of cardiovascular disease.

Mitochondrial quality control in cardiac fibrosis: Epigenetic mechanisms and therapeutic strategies

Cardiac fibrosis (CF) is considered an ultimate common pathway of a wide variety of heart diseases in response to diverse pathological and pathophysiological stimuli. Mitochondria are characterized as isolated organelles with a double-membrane structure, and they primarily contribute to and maintain highly dynamic energy and metabolic networks whose distribution and structure exert potent support for cellular properties and performance. Because the myocardium is a highly oxidative tissue with high energy demands to continuously pump blood, mitochondria are the most abundant organelles within mature cardiomyocytes, accounting for up to one-third of the total cell volume, and play an essential role in maintaining optimal performance of the heart. Mitochondrial quality control (MQC), including mitochondrial fusion, fission, mitophagy, mitochondrial biogenesis, and mitochondrial metabolism and biosynthesis, is crucial machinery that modulates cardiac cells and heart function by maintaining and regulating the morphological structure, function and lifespan of mitochondria. Certain investigations have focused on mitochondrial dynamics, including manipulating and maintaining the dynamic balance of energy demand and nutrient supply, and the resultant findings suggest that changes in mitochondrial morphology and function may contribute to bioenergetic adaptation during cardiac fibrosis and pathological remodeling. In this review, we discuss the function of epigenetic regulation and molecular mechanisms of MQC in the pathogenesis of CF and provide evidence for targeting MQC for CF. Finally, we discuss how these findings can be applied to improve the treatment and prevention of CF.

Txnip Gene Knockout Ameliorated High-Fat Diet-Induced Cardiomyopathy Via Regulating Mitochondria Dynamics and Fatty Acid Oxidation

ABSTRACT

Epidemic of obesity accelerates the increase in the number of patients with obesity cardiomyopathy. Thioredoxin interacting protein (TXNIP) has been implicated in the pathogenesis of multiple cardiovascular diseases. However, its specific role in obesity cardiomyopathy is still not well understood. Here, we evaluated the role of TXNIP in obesity-induced cardiomyopathy by feeding wild-type and txnip gene knockout mice with either normal diet or high-fat diet (HFD) for 24 weeks. Our results suggested that TXNIP deficiency improved mitochondrial dysfunction via reversing the shift from mitochondrial fusion to fission in the context of chronic HFD feeding, thus promoting cardiac fatty acid oxidation to alleviate chronic HFD-induced lipid accumulation in the heart, and thereby ameliorating the cardiac function in obese mice. Our work provides a theoretical basis for TXNIP exerting as a potential therapeutic target for the interventions of obesity cardiomyopathy.

Aryl hydrocarbon receptor maintains hepatic mitochondrial homeostasis in mice

OBJECTIVE

Mitophagy removes damaged mitochondria to maintain cellular homeostasis. Aryl hydrocarbon receptor (AhR) expression in the liver plays a crucial role in supporting normal liver functions, but its impact on mitochondrial function is unclear. Here, we identified a new role of AhR in the regulation of mitophagy to control hepatic energy homeostasis.

METHODS

In this study, we utilized primary hepatocytes from AhR knockout (KO) mice and AhR knockdown AML12 hepatocytes. An endogenous AhR ligand, kynurenine (Kyn), was used to activate AhR in AML12 hepatocytes. Mitochondrial function and mitophagy process were comprehensively assessed by MitoSOX and mt-Keima fluorescence imaging, Seahorse XF-based oxygen consumption rate measurement, and Mitoplate S-1 mitochondrial substrate utilization analysis.

RESULTS

Transcriptomic analysis indicated that mitochondria-related gene sets were dysregulated in AhR KO liver. In both primary mouse hepatocytes and AML12 hepatocyte cell lines, AhR inhibition strongly suppressed mitochondrial respiration rate and substrate utilization. AhR inhibition also blunted the fasting response of several essential autophagy genes and the mitophagy process. We further identified BCL2 interacting protein 3 (BNIP3), a mitophagy receptor that senses nutrient stress, as an AhR target gene. AhR is directly recruited to the Bnip3 genomic locus, and Bnip3 transcription was enhanced by AhR endogenous ligand treatment in wild-type liver and abolished entirely in AhR KO liver. Mechanistically, overexpression of Bnip3 in AhR knockdown cells mitigated the production of mitochondrial reactive oxygen species (ROS) and restored functional mitophagy.

CONCLUSIONS

AhR regulation of the mitophagy receptor BNIP3 coordinates hepatic mitochondrial function. Loss of AhR induces mitochondrial ROS production and impairs mitochondrial respiration. These findings provide new insight into how endogenous AhR governs hepatic mitochondrial homeostasis.

Mitochondrion: A bridge linking aging and degenerative diseases

Aging is a natural process, characterized by progressive loss of physiological integrity, impaired function, and increased vulnerability to death. For centuries, people have been trying hard to understand the process of aging and find effective ways to delay it. However, limited breakthroughs have been made in anti-aging area. Since the hallmarks of aging were summarized in 2013, increasing studies focus on the role of mitochondrial dysfunction in aging and aging-related degenerative diseases, such as neurodegenerative diseases, osteoarthritis, metabolic diseases, and cardiovascular diseases. Accumulating evidence indicates that restoring mitochondrial function and biogenesis exerts beneficial effects in extending lifespan and promoting healthy aging. In this paper, we provide an overview of mitochondrial changes during aging and summarize the advanced studies in mitochondrial therapies for the treatment of degenerative diseases. Current challenges and future perspectives are proposed to provide novel and promising directions for future research.

Polydatin inhibits mitochondrial damage and mitochondrial ROS by promoting PINK1-Parkin-mediated mitophagy in allergic rhinitis

Polydatin (PD), a natural product derived from Polygonum cuspidatum, has anti-inflammatory and antioxidant effects and has significant benefits in treating allergic diseases. However, its role and mechanism in allergic rhinitis (AR) have not been fully elucidated. Herein, we investigated the effect and mechanism of PD in AR. AR model was established in mice with OVA. Human nasal epithelial cells (HNEpCs) were stimulated with IL-13. HNEpCs were also treated with an inhibitor of mitochondrial division or transfected with siRNA. The levels of IgE and cellular inflammatory factors were examined by enzyme linked immunosorbent assay and flow cytometry. The expressions of PINK1, Parkin, P62, LC3B, NLRP3 inflammasome proteins, and apoptosis proteins in nasal tissues and HNEpCs were measured by Western blot. We found that PD suppressed OVA-induced epithelial thickening and eosinophil accumulation in the nasal mucosa, reduced IL-4 production in NALF, and regulated Th1/Th2 balance. In addition, mitophagy was induced in AR mice after OVA challenge and in HNEpCs after IL-13 stimulation. Meanwhile, PD enhanced PINK1-Parkin-mediated mitophagy but decreased mitochondrial reactive oxygen species (mtROS) production, NLRP3 inflammasome activation, and apoptosis. However, PD-induced mitophagy was abrogated after PINK1 knockdown or Mdivi-1 treatment, indicating a key role of the PINK1-Parkin in PD-induced mitophagy. Moreover, mitochondrial damage, mtROS production, NLRP3 inflammasome activation, and HNEpCs apoptosis under IL-13 exposure were more severe after PINK1 knockdown or Mdivi-1 treatment. Conclusively, PD may exert protective effects on AR by promoting PINK1-Parkin-mediated mitophagy, which further suppresses apoptosis and tissue damage in AR through decreasing mtROS production and NLRP3 inflammasome activation.

The Drp1-Mediated Mitochondrial Fission Protein Interactome as an Emerging Core Player in Mitochondrial Dynamics and Cardiovascular Disease Therapy

Mitochondria, the membrane-bound cell organelles that supply most of the energy needed for cell function, are highly regulated, dynamic organelles bearing the ability to alter both form and functionality rapidly to maintain normal physiological events and challenge stress to the cell. This amazingly vibrant movement and distribution of mitochondria within cells is controlled by the highly coordinated interplay between mitochondrial dynamic processes and fission and fusion events, as well as mitochondrial quality-control processes, mainly mitochondrial autophagy (also known as mitophagy). Fusion connects and unites neighboring depolarized mitochondria to derive a healthy and distinct mitochondrion. In contrast, fission segregates damaged mitochondria from intact and healthy counterparts and is followed by selective clearance of the damaged mitochondria via mitochondrial specific autophagy, i.e., mitophagy. Hence, the mitochondrial processes encompass all coordinated events of fusion, fission, mitophagy, and biogenesis for sustaining mitochondrial homeostasis. Accumulated evidence strongly suggests that mitochondrial impairment has already emerged as a core player in the pathogenesis, progression, and development of various human diseases, including cardiovascular ailments, the leading causes of death globally, which take an estimated 17.9 million lives each year. The crucial factor governing the fission process is the recruitment of dynamin-related protein 1 (Drp1), a GTPase that regulates mitochondrial fission, from the cytosol to the outer mitochondrial membrane in a guanosine triphosphate (GTP)-dependent manner, where it is oligomerized and self-assembles into spiral structures. In this review, we first aim to describe the structural elements, functionality, and regulatory mechanisms of the key mitochondrial fission protein, Drp1, and other mitochondrial fission adaptor proteins, including mitochondrial fission 1 (Fis1), mitochondrial fission factor (Mff), mitochondrial dynamics 49 (Mid49), and mitochondrial dynamics 51 (Mid51). The core area of the review focuses on the recent advances in understanding the role of the Drp1-mediated mitochondrial fission adaptor protein interactome to unravel the missing links of mitochondrial fission events. Lastly, we discuss the promising mitochondria-targeted therapeutic approaches that involve fission, as well as current evidence on Drp1-mediated fission protein interactions and their critical roles in the pathogeneses of cardiovascular diseases (CVDs).

Intrinsic Dynamics of the ClpXP Proteolytic Machine Using Elastic Network Models

ClpXP complex is an ATP-dependent mitochondrial matrix protease that binds, unfolds, translocates, and subsequently degrades specific protein substrates. Its mechanisms of operation are still being debated, and several have been proposed, including the sequential translocation of two residues (SC/2R), six residues (SC/6R), and even long-pass probabilistic models. Therefore, it has been suggested to employ biophysical-computational approaches that can determine the kinetics and thermodynamics of the translocation. In this sense, and based on the apparent inconsistency between structural and functional studies, we propose to apply biophysical approaches based on elastic network models (ENM) to study the intrinsic dynamics of the theoretically most probable hydrolysis mechanism. The proposed models ENM suggest that the ClpP region is decisive for the stabilization of the ClpXP complex, contributing to the flexibility of the residues adjacent to the pore, favoring the increase in pore size and, therefore, with the energy of interaction of its residues with a larger portion of the substrate. It is predicted that the complex may undergo a stable configurational change once assembled and that the deformability of the system once assembled is oriented, to increase the rigidity of the domains of each region (ClpP and ClpX) and to gain flexibility of the pore. Our predictions could suggest under the conditions of this study the mechanism of the interaction of the system, of which the substrate passes through the unfolding of the pore in parallel with a folding of the bottleneck. The variations in the distance calculated by molecular dynamics could allow the passage of a substrate with a size equivalent to ∼3 residues. The theoretical behavior of the pore and the stability and energy of binding to the substrate based on ENM models suggest that in this system, there are thermodynamic, structural, and configurational conditions that allow a possible translocation mechanism that is not strictly sequential.

MORN4 protects cardiomyocytes against ischemic injury via MFN2-mediated mitochondrial dynamics and mitophagy

The imbalance of mitochondrial fission and fusion dynamics causes ischemic cardiomyocyte apoptosis and heart injury by affecting mitophagy. Regulation of mitochondrial dynamics is an important therapeutic strategy for ischemic heart diseases. Considering the important roles of MORN motifs in heart diseases and chloroplast fission, we aimed to investigate the possible role of MORN repeat-containing protein 4 (MORN4) in the progression of myocardial infarction (MI), ischemic cardiomyocyte apoptosis, mitochondrial dynamics, and mitophagy. We found that in the MI mouse, MORN4 knockdown remarkably accelerated cardiac injury and fibrosis with deteriorating cardiac dysfunction. Sphingosylphosphorylcholine (SPC) alleviated ischemic cardiomyocyte apoptosis and heart injury through increased level of MORN4, indicating a vital function of MORN4 in heart with SPC used to clarify the molecular mechanisms underlying the functions of MORN4. Mechanistically, we found that MORN4 directly binds to MFN2 and promotes the phosphorylation of MFN2 S442 through Rho-associated protein kinase 2 (ROCK2), which mediates beneficial mitophagy induced by mitochondrial dynamics, while SPC promoted the binding of MORN4 and MFN2 and the process. Taken together, our data reveal a new perspective role of MORN4 in ischemic heart injury, and report that SPC could regulate myocardial mitochondrial homeostasis by activating the MORN4-MFN2 axis during the ischemic situation, this finding provides novel targets for improving myocardial ischemia tolerance and rescue of acute myocardial infarction.

The protective effect of inhibiting mitochondrial fission on the juvenile rat brain following PTZ kindling through inhibiting the BCL2L13/LC3 mitophagy pathway

Maintaining the balance of mitochondrial fission and mitochondrial autophagy on seizures is helpful to find a solution to control seizures and reduce brain injuries. The present study is to investigate the protective effect of inhibiting mitochondrial fission on brain injury in juvenile rat epilepsy induced by pentatetrazol (PTZ) by inhibiting the BCL2L13/LC3-mediated mitophagy pathway. PTZ was injected (40 mg/kg) to induce kindling once every other day, for a total of 15 times. In the PTZ + DMSO (DMSO), PTZ + Mdivi-1 (Mdivi-1), and PTZ + WY14643 (WY14643) groups, rats were pretreated with DMSO, Mdivi-1 and WY14643 for half an hour prior to PTZ injection. The seizure attacks of young rats were observed for 30 min after model establishment. The Morris water maze (MWM) was used to test the cognition of experimental rats. After the test, the numbers of NeuN(+) neurons and GFAP(+) astrocytes were observed and counted by immunofluorescence (IF). The protein expression levels of Drp1, BCL2L13, LC3 and caspase 3 in the hippocampus of young rats were detected by immunohistochemistry (IHC) and Western blotting (WB). Compared with the PTZ and DMSO groups, the seizure latency in the Mdivi-1 group was longer (P < 0.01), and the severity degree and frequency of seizures were lower (P < 0.01). The MWM test showed that the incubation periods of crossing the platform in the Mdivi-1 group was significantly shorter. The number of platform crossings, the platform stay time, and the ratio of residence time/total stay time were significantly increased in the Mdivi-1 group (P < 0.01). The IF results showed that the number of NeuN(+) neurons in the Mdivi-1 group was greater, while the number of GFAP(+) astrocytes was lower. IHC and WB showed that the average optical density (AOD) and relative protein expression levels of Drp1, BCL2L13, LC3 and caspase 3 in the hippocampi of rats in the Mdivi-1 group were higher (P < 0.05). The above results in the WY14643 group were opposite to those in the Mdivi-1 group. Inhibition of mitochondrial fission could reduce seizure attacks, protect injured neurons, and improve cognition following PTZ-induced epilepsy by inhibiting mitochondrial autophagy mediated by the BCL2L13/LC3 mitophagy pathway.

Site-specific ubiquitination of VDAC1 restricts its oligomerization and mitochondrial DNA release in liver fibrosis

Mitochondrial DNA (mtDNA) released through protein oligomers, such as voltage-dependent anion channel 1 (VDAC1), triggers innate immune activation and thus contributes to liver fibrosis. Here, we investigated the role of Parkin, an important regulator of mitochondria, and its regulation of VDAC1-mediated mtDNA release in liver fibrosis. The circulating mitochondrial DNA (mtDNA) and protein levels of liver Parkin and VDAC1 were upregulated in patients with liver fibrosis. A 4-week CCl₄ challenge induced release of mtDNA, activation of STING signaling, a decline in autophagy, and apoptosis in mouse livers, and the knockout of Parkin aggravated these effects. In addition, Parkin reduced mtDNA release and prevented VDAC1 oligomerization in a manner dependent on its E3 activity in hepatocytes. We found that site-specific ubiquitination of VDAC1 at lysine 53 by Parkin interrupted VDAC1 oligomerization and prevented mtDNA release into the cytoplasm under stress. The ubiquitination-defective VDAC1 K53R mutant predominantly formed oligomers that resisted suppression by Parkin. Hepatocytes expressing VDAC1 K53R exhibited mtDNA release and thus activated the STING signaling pathway in hepatic stellate cells, and this effect could not be abolished by Parkin. We propose that the ubiquitination of VDAC1 at a specific site by Parkin confers protection against liver fibrosis by interrupting VDAC1 oligomerization and mtDNA release.

Autophagy of naïve CD4+ T cells in aging - the role of body adiposity and physical fitness

Life expectancy has increased exponentially in the last century accompanied by disability, poor quality of life, and all-cause mortality in older age due to the high prevalence of obesity and physical inactivity in older people. Biologically, the aging process reduces the cell's metabolic and functional efficiency, and disrupts the cell's anabolic and catabolic homeostasis, predisposing older people to many dysfunctional conditions such as cardiovascular disease, neurodegenerative disorders, cancer, and diabetes. In the immune system, aging also alters cells' metabolic and functional efficiency, a process known as 'immunosenescence', where cells become more broadly inflammatory and their functionality is altered. Notably, autophagy, the conserved and important cellular process that maintains the cell's efficiency and functional homeostasis may protect the immune system from age-associated dysfunctional changes by regulating cell death in activated CD4+ T cells. This regulatory process increases the delivery of the dysfunctional cytoplasmic material to lysosomal degradation while increasing cytokine production, proliferation, and differentiation of CD4+ T cell-mediated immune responses. Poor proliferation and diminished responsiveness to cytokines appear to be ubiquitous features of aged T cells and may explain the delayed peak in T cell expansion and cytotoxic activity commonly observed in the 'immunosenescence' phenotype in the elderly. On the other hand, physical exercise stimulates the expression of crucial nutrient sensors and inhibits the mechanistic target of the rapamycin (mTOR) signaling cascade which increases autophagic activity in cells. Therefore, in this perspective review, we will first contextualize the overall view of the autophagy process and then, we will discuss how body adiposity and physical fitness may counteract autophagy in naïve CD4+ T cells in aging.

Alamandine/MrgD axis prevents TGF-β1-mediated fibroblast activation via regulation of aerobic glycolysis and mitophagy

BACKGROUND

Idiopathic pulmonary fibrosis is a chronic progressive, lethal disease in which ectopic lung fibroblast (LF) activation plays a vital part. We have previously shown that alamandine (ALA) exerts anti-fibrosis effects via the MAS-related G-protein coupled receptor D (MrgD). Here, we further investigate how it moderates transforming growth factor β1 (TGF-β1)-induced LF activation by regulating glucose metabolism and mitochondria autophagy (mitophagy).

METHODS

In vitro, we examined glycolysis-related protein hexokinase 2 (HK2), 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), and lactic acid in cells treated with TGF-β1. The oxygen consumption rate and the extracellular acidification rate were detected using Seahorse assays. Then, mitophagy was evaluated using transmission electron microscopy, mt-Keima, and the co-localization of Parkin and COX IV with LC3 and LAMP1, respectively. The autophagic degradation of HK2 and PFKFB3 was detected by 3MA and bafilomycin A1 and assessed by their co-localization with LC3 and LAMP1, respectively. The effects of ALA on LF activation markers collagen I and α-SMA were detected. The effects of ALA on glucose metabolism, mitophagy, and the activation of LF were also investigated in vivo.

RESULTS

We found that the ALA/MrgD axis improved TGF-β1-mediated LF activation by repressing glycolysis by downregulating HK2 and PFKFB3 expression. Lactic acid sustained positive feedback between glycolysis and LF activation by maintaining the expression of HK2 and PFKFB3. We also showed that glycolysis enhancement resulted from blocking the autophagic degradation of HK2 and PFKFB3 while upregulated mRNA levels by TGF-β1, while all of those improved by ALA adding. Importantly, we determined that moderation of Parkin/LC3-mediated mitophagy by TGF-β1 also promotes glycolysis but is reversed by ALA. Furthermore, we proved that ALA counteracts the effects of bleomycin on HK2, PFKFB3, LC3, Parkin, and LF activation in vivo.

CONCLUSION

In this study, we show that the ALA/MrgD axis prevents TGF-β1-mediated fibroblast activation via regulation of aerobic glycolysis and mitophagy.

Early cardiac aging linked to impaired stress-resistance and transcriptional control of stress response, quality control and mitochondrial pathways

Phenotypic and transcriptomic evidence of early cardiac aging, and associated mechanisms, were investigated in young to middle-aged male mice (C57Bl/6; ages 8, 16, 32, 48 wks). Left ventricular gene expression (profiled via Illumina MouseWG-6 BeadChips), contractile and coronary function, and stress-resistance were assessed in Langendorff perfused hearts under normoxic conditions and following ischemic insult (20 min global ischemia-45 min reperfusion; I-R). Baseline or normoxic contractile function was unaltered by age, while cardiac and coronary 'reserves' (during β-adrenoceptor stimulation; 1 μM isoproterenol) declined by 48 wks. Resistance to I-R injury fell from 16 to 32 wks. Age-dependent transcriptional changes In un-stressed hearts were limited to 104 genes (>1.3-fold; 0.05 FDR), supporting: up-regulated innate defenses (glutathione and xenobiotic metabolism, chemotaxis, interleukins) and catecholamine secretion; and down-regulated extracellular matrix (ECM), growth factor and survival (PI3K/Akt) signaling. In stressed (post-ischemic) myocardium, ∼15-times as many genes (1528) were age-dependent, grouped into 6 clusters (>1.3-fold change; 0.05 FDR): most changing from 16 wks (45 % up/44 % down), a further 5 % declining from 32 wks. Major age-dependent Biological Processes in I-R hearts reveal: declining ATP metabolism, oxidative phosphorylation, cardiac contraction and morphogenesis, phospholipid metabolism and calcineurin signaling; increasing proteolysis and negative control of MAPK; and mixed changes in nuclear transport and angiogenic genes. Pathway analysis supports reductions in: autophagy, stress response, ER protein processing, mRNA surveillance and ribosome/translation genes; with later falls in mitochondrial biogenesis, oxidative phosphorylation and proteasome genes in I-R hearts. Summarizing, early cardiac aging is evident from 16 to 32 wks in male mice, characterized by: declining cardiovascular reserve and stress-resistance, transcriptomic evidence of constitutive stress and altered catecholamine and survival/growth signaling in healthy hearts; and declining stress response, quality control, mitochondrial energy metabolism and cardiac modeling processes in stressed hearts. These very early changes, potentially key substrate for advanced aging, may inform approaches to healthy aging and cardioprotection in the adult heart.

Mitochondrial quality control mechanisms as therapeutic targets in doxorubicin-induced cardiotoxicity

Doxorubicin (DOX) is a chemotherapeutic drug that is utilized for solid tumors and hematologic malignancies, but its clinical application is hampered by life-threatening cardiotoxicity including cardiac dilation and heart failure. Mitochondrial quality control processes, including mitochondrial proteostasis, mitophagy, and mitochondrial dynamics and biogenesis, serve to maintain mitochondrial homeostasis in the cardiovascular system. Importantly, recent advances have unveiled a major role for defective mitochondrial quality control in the etiology of DOX cardiomyopathy. Moreover, specific interventions targeting these quality control mechanisms to preserve mitochondrial function have emerged as potential therapeutic strategies to attenuate DOX cardiotoxicity. However, clinical translation is challenging because of obscure mechanisms of action and potential adverse effects. The purpose of this review is to provide new insights regarding the role of mitochondrial quality control in the pathogenesis of DOX cardiotoxicity, and to explore promising therapeutic approaches targeting these mechanisms to aid clinical management.

Tobacco smoke exposure and mitochondrial DNA copy number on neurobehavioural performance: A community study

The influence of tobacco smoke has been a controversial and very questionable subject within the field of neurological behaviours. To examine the dose-response relationships between tobacco smoke and neurological performance, we investigated whether mitochondrial DNA copy number (mtDNAcn) mediates these relationships. We used restricted cubic spline models to estimate the dose-response relationships. A mediation model was also used to detect the mediating effect. Increased cotinine was negatively associated with auditory memory scores and a 0.51 decrease in mtDNAcn. MtDNAcn acts as a mediator between cotinine and auditory memory. Tobacco smoke levels were inversely associated with mtDNAcn and neurobehavioural changes, and there was a mediation effect between cotinine levels and auditory memory by mtDNAcn.

O-GlcNAcylation of SIRT1 Protects against Cold Stress-Induced Skeletal Muscle Damage via Amelioration of Mitochondrial Homeostasis

Cold stress disturbs cellular metabolic and energy homeostasis, which is one of the causes of stress-induced illnesses. O-GlcNAcylation is a nutrient-sensing pathway involved in a myriad of cellular processes. It plays a key role in metabolic homeostasis. Nevertheless, a specific sensing mechanism linking skeletal muscle to O-GlcNAcylation in cold stress is unknown. In this study, O-GlcNAcylation of SIRT1 was targeted to explore the mechanism of skeletal muscle adaptation to cold stress. Ogt mKO aggravated skeletal muscle fibrosis induced by cold stress. At the same time, Ogt gene deletion accelerated the homeostasis imbalance and oxidative stress of skeletal muscle mitochondria induced by cold stress. In vitro results showed that inhibition of SIRT1's O-GlcNAcylation accelerated mild hypothermia induced mitochondrial homeostasis in mouse myogenic cells (C2C12 cells). However, overexpression of SIRT1's O-GlcNAcylation improved the above phenomena. Thus, these results reveal a protective role of OGT-SIRT1 in skeletal muscle's adaptation to cold stress, and our findings will provide new avenues to combat stress-induced diseases.

Mammary Fibrosis Tendency and Mitochondrial Adaptability in Dairy Cows with Mastitis

Dairy cow mammary gland fibrosis causes huge economic losses to livestock production, however, research on dairy cow mammary gland fibrosis is in its infancy and it lacks effective treatments. Therefore, the purpose of this experiment was to explore the correlation between mastitis and fibrosis and mitochondrial damage, and to further explore its pathogenesis. In vivo, mammary tissue and milk samples were collected from healthy cows (n = 10) and mastitis cows (n = 10). The results of the study showed that compared with the control group, the mastitis tissue showed tissue damage, accumulation of collagen fibers, and the content of TGF-β1 in mammary tissue and milk was significantly increased; the level of inflammatory mediators was significantly increased; the fibrotic phenotype, collagen 1, α-SMA, vimentin gene, and protein levels were significantly increased, while the E-cadherin gene and protein levels were significantly decreased. In vitro, based on TGF-β1-induced bMECs, the above experimental results were further confirmed, and TGF-β1 significantly promoted the fibrotic phenotype of bMECs. On the other hand, in vivo results showed that fibrotic mammary tissue had a significantly stronger mitochondrial damage phenotype and significantly higher ROS than the control group. In vitro, the results also found that TGF-β1 induced a significant increase in the mitochondrial damage phenotype of bMECs, accompanied by a large amount of ROS production. Furthermore, in a TGF-β1-induced bMEC model, inhibiting the accumulation of ROS effectively alleviated the elevated fibrotic phenotype of TGF-β1-induced bMECs. In conclusion, the fibrotic phenotype of mammary gland tissue in dairy cows with mastitis was significantly increased, and mastitis disease was positively correlated with mammary fibrotic lesions. In an in vitro and in vivo model of cow mammary fibrosis, bMECs have impaired mitochondrial structure and dysfunction. Inhibiting the accumulation of ROS effectively alleviates the elevated fibrotic phenotype, which may be a potential therapeutic approach to alleviate mammary fibrosis.

Novel insights into exhaustive exercise-induced myocardial injury: Focusing on mitochondrial quality control

Regular moderate-intensity exercise elicits benefit cardiovascular health outcomes. However, exhaustive exercise (EE) triggers arrhythmia, heart failure, and sudden cardiac death. Therefore, a better understanding of unfavorable heart sequelae of EE is important. Various mechanisms have been postulated for EE-induced cardiac injury, among which mitochondrial dysfunction is considered the cardinal machinery for pathogenesis of various diseases. Mitochondrial quality control (MQC) is critical for clearance of long-lived or damaged mitochondria, regulation of energy metabolism and cell apoptosis, maintenance of cardiac homeostasis and alleviation of EE-induced injury. In this review, we will focus on MQC mechanisms and propose mitochondrial pathophysiological targets for the management of EE-induced myocardial injury. A thorough understanding of how MQC system functions in the maintenance of mitochondrial homeostasis will provide a feasible rationale for developing potential therapeutic interventions for EE-induced injury.

Silica nanoparticles perturbed mitochondrial dynamics and induced myocardial apoptosis via PKA-DRP1-mitochondrial fission signaling

Silica nanoparticles (SiNPs) are among the most abundantly produced nanosized particles in the global market, and their potential toxicity has aroused a great concern. Increasing epidemiological investigations and experimental evidence revealed the threaten of SiNPs exposure to cardiovascular system. The myocardial toxicity caused by SiNPs was gradually demonstrated, nevertheless, the underlying mechanisms remain unclear. In view of mitochondria serving as the centrality in the prominent of cardiovascular disease, we investigated the role of mitochondria and related mechanisms in SiNPs-induced adverse effects on cardiomyocytes. As a result, SiNPs were found in cytoplasm, accompanied with morphological alterations in mitochondria, such as cristae fracture or disappearance, vacuolation. The induction of mitochondrial dysfunction by SiNPs was confirmed, as indicated by the excessive reactive oxygen species (ROS) formation, and blockage of cellular respiratory and ATP production. Concomitantly, SiNPs activated mitochondria-mediated apoptotic signaling in view of the up-regulated BAX, increased Caspase-9 cleavage and declined Bcl-2, ultimately resulting in myocardial apoptosis. It was noteworthy that SiNPs disturbed mitochondrial dynamics toward fission phenotype, which was supported by the dysregulated fission/fusion regulators. Especially, DRP1 and its phosphorylated level at s616 (p-DRP1^s616) were up-regulated, whilst its phosphorylated level at s637 (p-DRP1^s637) and PKA phosphorylation were down-regulated in SiNPs-treated cardiomyocytes in a dose-dependent manner. More importantly, the mechanistic investigations revealed PKA-DRP1-mediated mitochondrial fission was responsible for SiNPs-induced cardiomyocyte apoptosis through the mitochondria-mediated apoptotic way. This study firstly demonstrated the disturbance of mitochondrial dynamics played a crucial role in cardiomyocyte apoptosis caused by SiNPs, attributing to PKA-DRP1-mitochondrial fission signaling.

Mitophagy in cardiovascular diseases: molecular mechanisms, pathogenesis, and treatment

With the growing prevalence of cardiovascular disease (CVD), there is an urgent need to explore non-conventional therapeutic measures to alleviate the burden of CVD on global healthcare. Mitochondrial injury plays a cardinal role in the pathogenesis of CVD. Mitochondrial dynamics and mitophagy are essential machineries that govern mitochondrial health in cardiomyocytes in physiological and pathophysiological settings. However, with the onset and progression of CVD, homeostasis of mitophagy is disturbed through largely unknown pathological mechanisms, causing mitochondrial damage and ultimately cardiomyocyte death. In this review we decipher the dual regulatory role of mitophagy in CVD pathogenesis, summarize controversies in mitophagy, and highlight recently identified compounds capable of modulating mitophagy. We share our perspectives on future mitophagy research directions in the context of CVD.

Downregulation of SIRT3 Aggravates Lung Ischemia Reperfusion Injury by Increasing Mitochondrial Fission and Oxidative Stress through HIF-1α-Dependent Mechanisms

Lung ischemia-reperfusion injury (LIRI) is a severe multifaceted pathological condition that can lead to poor patient outcome where oxidative stress and the resulting inflammatory response can trigger and exacerbate tissue damage in LIRI patients. Sirtuin3 (SIRT3), a member of the sirtuin family, protects against oxidative stress-related diseases. However, it remains unclear if and how SIRT3 alleviates lung injury induced by ischemia/reperfusion (I/R). Our previous study showed that lung tissue structures were severely damaged at 6 h after lung I/R in mice, however, repair of the injured lung tissue was significant at 24 h. In this study, we found that both SIRT3 mRNA and protein levels were markedly increased at 24 h after lung I/R in vivo. Meanwhile, inhibition of SIRT3 aggravated lung injury and inflammation, augmented mitochondrial fission and oxidative stress and increased Hypoxia-inducible factor-1α (HIF-1α) expression in vivo. The results suggest that SIRT3 may be an upstream regulator of HIF-1α expression. Knockdown of SIRT3 resulted in excessive mitochondrial fission and increased oxidative stress in vitro, and we found that knocking down the expression of HIF-1α alleviated these changes. This suggests that the SIRT3-HIF-1α signaling pathway is involved in regulating mitochondrial function and oxidative stress. Furthermore, inhibition of dynamin-related protein 1 (Drp-1) by the inhibitor of mitophagy, Mdivi-1, blocked mitochondrial fission and alleviated oxidative stress in vitro. Taken together, our results demonstrated that downregulation of SIRT3 aggravates LIRI by increasing mitochondrial fission and oxidative stress. Activation of SIRT3 inhibits mitochondrial fission and this mechanism may serve as a new therapeutic strategy to treat LIRI.

PGC-1α activity and mitochondrial dysfunction in preterm infants

Extremely low gestational age neonates (ELGANs) are born in a relatively hyperoxic environment with weak antioxidant defenses, placing them at high risk for mitochondrial dysfunction affecting multiple organ systems including the nervous, respiratory, ocular, and gastrointestinal systems. The brain and lungs are highly affected by mitochondrial dysfunction and dysregulation in the neonate, causing white matter injury (WMI) and bronchopulmonary dysplasia (BPD), respectively. Adequate mitochondrial function is important in providing sufficient energy for organ development as it relates to alveolarization and axonal myelination and decreasing oxidative stress via reactive oxygen species (ROS) and reactive nitrogen species (RNS) detoxification. Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) is a master regulator of mitochondrial biogenesis and function. Since mitochondrial dysfunction is at the root of WMI and BPD pathobiology, exploring therapies that can regulate PGC-1α activity may be beneficial. This review article describes several promising therapeutic agents that can mitigate mitochondrial dysfunction through direct and indirect activation and upregulation of the PGC-1α pathway. Metformin, resveratrol, omega 3 fatty acids, montelukast, L-citrulline, and adiponectin are promising candidates that require further pre-clinical and clinical studies to understand their efficacy in decreasing the burden of disease from WMI and BPD in preterm infants.