Motif affinity and mass spectrometry proteomic approach for the discovery of cellular AMPK targets: Identification of mitochondrial fission factor as a new AMPK substrate

Traditional Chinese medicine and mitophagy: A novel approach for cardiovascular disease management

BACKGROUND

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality worldwide, imposing an enormous economic burden on individuals and human society. Laboratory studies have identified several drugs that target mitophagy for the prevention and treatment of CVD. Only a few of these drugs have been successful in clinical trials, and most studies have been limited to animal and cellular models. Furthermore, conventional drugs used to treat CVD, such as antiplatelet agents, statins, and diuretics, often result in adverse effects on patients' cardiovascular, metabolic, and respiratory systems. In contrast, traditional Chinese medicine (TCM) has gained significant attention for its unique theoretical basis and clinical efficacy in treating CVD.

PURPOSE

This paper systematically summarizes all the herbal compounds, extracts, and active monomers used to target mitophagy for the treatment of CVD in the last five years. It provides valuable information for researchers in the field of basic cardiovascular research, pharmacologists, and clinicians developing herbal medicines with fewer side effects, as well as a useful reference for future mitophagy research.

METHODS

The search terms "cardiovascular disease," "mitophagy," "herbal preparations," "active monomers," and "cardiac disease pathogenesis" in combination with "natural products" and "diseases" were used to search for studies published in the past five years until January 2024.

RESULTS

Studies have shown that mitophagy plays a significant role in the progression and development of CVD, such as atherosclerosis (AS), heart failure (HF), myocardial infarction (MI), myocardial ischemia/reperfusion injury (MI/RI), cardiac hypertrophy, cardiomyopathy, and arrhythmia. Herbal compound preparations, crude extracts, and active monomers have shown potential as effective treatments for these conditions. These substances protect cardiomyocytes by inducing mitophagy, scavenging damaged mitochondria, and maintaining mitochondrial homeostasis. They display notable efficacy in combating CVD.

CONCLUSION

TCM (including herbal compound preparations, extracts, and active monomers) can treat CVD through various pharmacological mechanisms and signaling pathways by inducing mitophagy. They represent a hotspot for future cardiovascular basic research and a promising candidate for the development of future cardiovascular drugs with fewer side effects and better therapeutic efficacy.

Food perception promotes phosphorylation of MFFS131 and mitochondrial fragmentation in liver

Liver mitochondria play a central role in metabolic adaptations to changing nutritional states, yet their dynamic regulation upon anticipated changes in nutrient availability has remained unaddressed. Here, we found that sensory food perception rapidly induced mitochondrial fragmentation in the liver through protein kinase B/AKT (AKT)-dependent phosphorylation of serine 131 of the mitochondrial fission factor (MFFS131). This response was mediated by activation of hypothalamic pro-opiomelanocortin (POMC)-expressing neurons. A nonphosphorylatable MFFS131G knock-in mutation abrogated AKT-induced mitochondrial fragmentation in vitro. In vivo, MFFS131G knock-in mice displayed altered liver mitochondrial dynamics and impaired insulin-stimulated suppression of hepatic glucose production. Thus, rapid activation of a hypothalamus-liver axis can adapt mitochondrial function to anticipated changes of nutritional state in control of hepatic glucose metabolism.

3-O-Methyl-D-Glucose Blunts Cold Ischemia Damage in Kidney via Inhibiting Ferroptosis

BACKGROUND

The glucose derivative 3-O-methyl-D-glucose (OMG) is used as a cryoprotectant in freezing cells. However, its protective role and the related mechanism in static cold storage (CS) of organs are unknown. The present study aimed to investigate the effect of OMG on cod ischemia damage in cold preservation of donor kidney.

METHODS

Pretreatment of OMG on kidney was performed in an isolated renal cold storage model in rats. LDH activity in renal efflux was used to evaluate the cellular damage. Indicators including iron levels, mitochondrial damage, MDA level, and cellular apoptosis were measured. Kidney quality was assessed via a kidney transplantation (KTx) model in rats. The grafted animals were followed up for 7 days. Ischemia reperfusion (I/R) injury and inflammatory response were assessed by biochemical and histological analyses.

RESULTS

OMG pretreatment alleviated prolonged CS-induced renal damage as evidenced by reduced LDH activities and tubular apoptosis. Kidney with pCS has significantly increased iron, MDA, and TUNEL+ cells, implying the increased ferroptosis, which has been partly inhibited by OMG. OMG pretreatment has improved the renal function (p <0.05) and prolonged the 7-day survival of the grafting recipients after KTx, as compared to the control group. OMG has significantly decreased inflammation and tubular damage after KTx, as evidenced by CD3-positive cells and TUNEL-positive cells.

CONCLUSION

Our study demonstrated that OMG protected kidney against the prolonged cold ischemia-caused injuries through inhibiting ferroptosis. Our results suggested that OMG might have potential clinical application in cold preservation of donor kidney.

Mitochondrial network dynamics in pulmonary disease: Bridging the gap between inflammation, oxidative stress, and bioenergetics

Once thought of in terms of bioenergetics, mitochondria are now widely accepted as both the orchestrator of cellular health and the gatekeeper of cell death. The pulmonary disease field has performed extensive efforts to explore the role of mitochondria in regulating inflammation, cellular metabolism, apoptosis, and oxidative stress. However, a critical component of these processes needs to be more studied: mitochondrial network dynamics. Mitochondria morphologically change in response to their environment to regulate these processes through fusion, fission, and mitophagy. This allows mitochondria to adapt their function to respond to cellular requirements, a critical component in maintaining cellular homeostasis. For that reason, mitochondrial network dynamics can be considered a bridge that brings multiple cellular processes together, revealing a potential pathway for therapeutic intervention. In this review, we discuss the critical modulators of mitochondrial dynamics and how they are affected in pulmonary diseases, including chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), acute lung injury (ALI), and pulmonary arterial hypertension (PAH). A dysregulated mitochondrial network plays a crucial role in lung disease pathobiology, and aberrant fission/fusion/mitophagy pathways are druggable processes that warrant further exploration. Thus, we also discuss the candidates for lung disease therapeutics that regulate mitochondrial network dynamics.

Functional, structural, and molecular remodelling of the goldfish (Carassius auratus) heart under moderate hypoxia

The goldfish (Carassius auratus) is known for its physiologic ability to survive even long periods of oxygen limitation (hypoxia), adapting the cardiac performance to the requirements of peripheral tissue perfusion. We here investigated the effects of short-term moderate hypoxia on the heart, focusing on ventricular adaptation, in terms of hemodynamics and structural traits. Functional evaluations revealed that animals exposed to 4 days of environmental hypoxia increased the hemodynamic performance evaluated on ex vivo cardiac preparations. This was associated with a thicker and more vascularized ventricular compact layer and a reduced luminal lacunary space. Compared to normoxic animals, ventricular cardiomyocytes of goldfish exposed to hypoxia showed an extended mitochondrial compartment and a modulation of proteins involved in mitochondria dynamics. The enhanced expression of the pro-fission markers DRP1 and OMA1, and the modulation of the short and long forms of OPA1, suggested a hypoxia-related mitochondria fission. Our data propose that under hypoxia, the goldfish heart undergoes a structural remodelling associated with a potentiated cardiac activity. The energy demand for the highly performant myocardium is supported by an increased number of mitochondria, likely occurring through fission events.

Cingulin family: Structure, function and clinical significance

Cingulin and its paralog paracingulin are vital components of the apical junctional complex in vertebrate epithelial and endothelial cells. They are both found in tight junctions (TJ), and paracingulin is also detectable in adherens junctions (AJ) as TJ cytoplasmic plaque proteins. Cingulin and paracingulin interact with other proteins to perform functions. They interact with cytoskeletal proteins, modulate the activity of small GTPases, such as RhoA and Rac1, and regulate gene expression. In addition, cingulin and paracingulin regulate barrier function and many pathological processes, including inflammation and tumorigenesis. In this review, we summarize the discovery and structure, expression and subcellular distribution, and molecular interactions of cingulin family proteins and discuss their role in development, physiology, and pathological processes.

TBC1D23 mediates Golgi-specific LKB1 signaling

Liver kinase B1 (LKB1), an evolutionarily conserved serine/threonine kinase, is a master regulator of the AMPK subfamily and controls cellular events such as polarity, proliferation, and energy homeostasis. Functions and mechanisms of the LKB1-AMPK axis at specific subcellular compartments, such as lysosome and mitochondria, have been established. AMPK is known to be activated at the Golgi; however, functions and regulatory mechanisms of the LKB1-AMPK axis at the Golgi apparatus remain elusive. Here, we show that TBC1D23, a Golgi-localized protein that is frequently mutated in the neurodevelopment disorder pontocerebellar hypoplasia (PCH), is specifically required for the LKB1 signaling at the Golgi. TBC1D23 directly interacts with LKB1 and recruits LKB1 to Golgi, promoting Golgi-specific activation of AMPK upon energy stress. Notably, Golgi-targeted expression of LKB1 rescues TBC1D23 deficiency in zebrafish models. Furthermore, the loss of LKB1 causes neurodevelopmental abnormalities in zebrafish, which partially recapitulates defects in TBC1D23-deficient zebrafish, and LKB1 sustains normal neuronal development via TBC1D23 interaction. Our study uncovers a regulatory mechanism of the LKB1 signaling, and reveals that a disrupted Golgi-LKB1 signaling underlies the pathogenesis of PCH.

Cellular Senescence, Mitochondrial Dysfunction, and Their Link to Cardiovascular Disease

Cardiovascular diseases (CVDs), a group of disorders affecting the heart or blood vessels, are the primary cause of death worldwide, with an immense impact on patient quality of life and disability. According to the World Health Organization, CVD takes an estimated 17.9 million lives each year, where more than four out of five CVD deaths are due to heart attacks and strokes. In the decades to come, an increased prevalence of age-related CVD, such as atherosclerosis, coronary artery stenosis, myocardial infarction (MI), valvular heart disease, and heart failure (HF) will contribute to an even greater health and economic burden as the global average life expectancy increases and consequently the world's population continues to age. Considering this, it is important to focus our research efforts on understanding the fundamental mechanisms underlying CVD. In this review, we focus on cellular senescence and mitochondrial dysfunction, which have long been established to contribute to CVD. We also assess the recent advances in targeting mitochondrial dysfunction including energy starvation and oxidative stress, mitochondria dynamics imbalance, cell apoptosis, mitophagy, and senescence with a focus on therapies that influence both and therefore perhaps represent strategies with the most clinical potential, range, and utility.

Mitochondrial phosphoproteomes are functionally specialized across tissues

Mitochondria are essential organelles whose dysfunction causes human pathologies that often manifest in a tissue-specific manner. Accordingly, mitochondrial fitness depends on versatile proteomes specialized to meet diverse tissue-specific requirements. Increasing evidence suggests that phosphorylation may play an important role in regulating tissue-specific mitochondrial functions and pathophysiology. Building on recent advances in mass spectrometry (MS)-based proteomics, we here quantitatively profile mitochondrial tissue proteomes along with their matching phosphoproteomes. We isolated mitochondria from mouse heart, skeletal muscle, brown adipose tissue, kidney, liver, brain, and spleen by differential centrifugation followed by separation on Percoll gradients and performed high-resolution MS analysis of the proteomes and phosphoproteomes. This in-depth map substantially quantifies known and predicted mitochondrial proteins and provides a resource of core and tissue-specific mitochondrial proteins (mitophos.de). Predicting kinase substrate associations for different mitochondrial compartments indicates tissue-specific regulation at the phosphoproteome level. Illustrating the functional value of our resource, we reproduce mitochondrial phosphorylation events on dynamin-related protein 1 responsible for its mitochondrial recruitment and fission initiation and describe phosphorylation clusters on MIGA2 linked to mitochondrial fusion.

Kinase signalling adaptation supports dysfunctional mitochondria in disease

Mitochondria form a critical control nexus which are essential for maintaining correct tissue homeostasis. An increasing number of studies have identified dysregulation of mitochondria as a driver in cancer. However, which pathways support and promote this adapted mitochondrial function? A key hallmark of cancer is perturbation of kinase signalling pathways. These pathways include mitogen activated protein kinases (MAPK), lipid secondary messenger networks, cyclic-AMP-activated (cAMP)/AMP-activated kinases (AMPK), and Ca2+/calmodulin-dependent protein kinase (CaMK) networks. These signalling pathways have multiple substrates which support initiation and persistence of cancer. Many of these are involved in the regulation of mitochondrial morphology, mitochondrial apoptosis, mitochondrial calcium homeostasis, mitochondrial associated membranes (MAMs), and retrograde ROS signalling. This review will aim to both explore how kinase signalling integrates with these critical mitochondrial pathways and highlight how these systems can be usurped to support the development of disease. In addition, we will identify areas which require further investigation to fully understand the complexities of these regulatory interactions. Overall, this review will emphasize how studying the interaction between kinase signalling and mitochondria improves our understanding of mitochondrial homeostasis and can yield novel therapeutic targets to treat disease.

Berberine Induces Mitophagy through Adenosine Monophosphate-Activated Protein Kinase and Ameliorates Mitochondrial Dysfunction in PINK1 Knockout Mouse Embryonic Fibroblasts

Mitophagy stimulation has been shown to have a therapeutic effect on various neurodegenerative diseases. However, nontoxic mitophagy inducers are still very limited. In this study, we found that the natural alkaloid berberine exhibited mitophagy stimulation activity in various human cells. Berberine did not interfere with mitochondrial function, unlike the well-known mitophagy inducer carbonyl cyanide m-chlorophenyl hydrazone (CCCP), and subsequently induced mitochondrial biogenesis. Berberine treatment induced the activation of adenosine monophosphate-activated protein kinase (AMPK), and the AMPK inhibitor compound C abolished berberine-induced mitophagy, suggesting that AMPK activation is essential for berberine-induced mitophagy. Notably, berberine treatment reversed mitochondrial dysfunction in PINK1 knockout mouse embryonic fibroblasts. Our results suggest that berberine is a mitophagy-specific inducer and can be used as a therapeutic treatment for neurodegenerative diseases, including Parkinson's disease, and that natural alkaloids are potential sources of mitophagy inducers.

Calcium signals tune AMPK activity and mitochondrial homeostasis in dendrites of developing neurons

Dendritic outgrowth in immature neurons is enhanced by neuronal activity and is considered one of the mechanisms of neural circuit optimization. It is known that calcium signals affect transcriptional regulation and cytoskeletal remodeling necessary for dendritic outgrowth. Here, we demonstrate that activity-dependent calcium signaling also controls mitochondrial homeostasis via AMP-activated protein kinase (AMPK) in growing dendrites of differentiating mouse hippocampal neurons. We found that the inhibition of neuronal activity induced dendritic hypotrophy with abnormally elongated mitochondria. In growing dendrites, AMPK is activated by neuronal activity and dynamically oscillates in synchrony with calcium spikes, and this AMPK oscillation was inhibited by CaMKK2 knockdown. AMPK activation led to phosphorylation of MFF and ULK1, which initiate mitochondrial fission and mitophagy, respectively. Dendritic mitochondria in AMPK-depleted neurons exhibited impaired fission and mitophagy and displayed multiple signs of dysfunction. Genetic inhibition of fission led to dendritic hypoplasia that was reminiscent of AMPK-deficient neurons. Thus, AMPK activity is finely tuned by the calcium-CaMKK2 pathway and regulates mitochondrial homeostasis by facilitating removal of damaged components of mitochondria in growing neurons during normal brain development.

Mitochondrial Dynamics: Working with the Cytoskeleton and Intracellular Organelles to Mediate Mechanotransduction

Cells are constantly exposed to various mechanical environments; therefore, it is important that they are able to sense and adapt to changes. It is known that the cytoskeleton plays a critical role in mediating and generating extra- and intracellular forces and that mitochondrial dynamics are crucial for maintaining energy homeostasis. Nevertheless, the mechanisms by which cells integrate mechanosensing, mechanotransduction, and metabolic reprogramming remain poorly understood. In this review, we first discuss the interaction between mitochondrial dynamics and cytoskeletal components, followed by the annotation of membranous organelles intimately related to mitochondrial dynamic events. Finally, we discuss the evidence supporting the participation of mitochondria in mechanotransduction and corresponding alterations in cellular energy conditions. Notable advances in bioenergetics and biomechanics suggest that the mechanotransduction system composed of mitochondria, the cytoskeletal system, and membranous organelles is regulated through mitochondrial dynamics, which may be a promising target for further investigation and precision therapies.

Mitochondrial dynamics in health and disease: mechanisms and potential targets

Mitochondria are organelles that are able to adjust and respond to different stressors and metabolic needs within a cell, showcasing their plasticity and dynamic nature. These abilities allow them to effectively coordinate various cellular functions. Mitochondrial dynamics refers to the changing process of fission, fusion, mitophagy and transport, which is crucial for optimal function in signal transduction and metabolism. An imbalance in mitochondrial dynamics can disrupt mitochondrial function, leading to abnormal cellular fate, and a range of diseases, including neurodegenerative disorders, metabolic diseases, cardiovascular diseases and cancers. Herein, we review the mechanism of mitochondrial dynamics, and its impacts on cellular function. We also delve into the changes that occur in mitochondrial dynamics during health and disease, and offer novel perspectives on how to target the modulation of mitochondrial dynamics.

The Role of Mitochondrial Dynamics and Mitotic Fission in Regulating the Cell Cycle in Cancer and Pulmonary Arterial Hypertension: Implications for Dynamin-Related Protein 1 and Mitofusin2 in Hyperproliferative Diseases

Mitochondria, which generate ATP through aerobic respiration, also have important noncanonical functions. Mitochondria are dynamic organelles, that engage in fission (division), fusion (joining) and translocation. They also regulate intracellular calcium homeostasis, serve as oxygen-sensors, regulate inflammation, participate in cellular and organellar quality control and regulate the cell cycle. Mitochondrial fission is mediated by the large GTPase, dynamin-related protein 1 (Drp1) which, when activated, translocates to the outer mitochondrial membrane (OMM) where it interacts with binding proteins (Fis1, MFF, MiD49 and MiD51). At a site demarcated by the endoplasmic reticulum, fission proteins create a macromolecular ring that divides the organelle. The functional consequence of fission is contextual. Physiological fission in healthy, nonproliferating cells mediates organellar quality control, eliminating dysfunctional portions of the mitochondria via mitophagy. Pathological fission in somatic cells generates reactive oxygen species and triggers cell death. In dividing cells, Drp1-mediated mitotic fission is critical to cell cycle progression, ensuring that daughter cells receive equitable distribution of mitochondria. Mitochondrial fusion is regulated by the large GTPases mitofusin-1 (Mfn1) and mitofusin-2 (Mfn2), which fuse the OMM, and optic atrophy 1 (OPA-1), which fuses the inner mitochondrial membrane. Mitochondrial fusion mediates complementation, an important mitochondrial quality control mechanism. Fusion also favors oxidative metabolism, intracellular calcium homeostasis and inhibits cell proliferation. Mitochondrial lipids, cardiolipin and phosphatidic acid, also regulate fission and fusion, respectively. Here we review the role of mitochondrial dynamics in health and disease and discuss emerging concepts in the field, such as the role of central versus peripheral fission and the potential role of dynamin 2 (DNM2) as a fission mediator. In hyperproliferative diseases, such as pulmonary arterial hypertension and cancer, Drp1 and its binding partners are upregulated and activated, positing mitochondrial fission as an emerging therapeutic target.

Testis-specific serine kinase 3 is required for sperm morphogenesis and male fertility

BACKGROUND

The importance of phosphorylation in sperm during spermatogenesis has not been pursued extensively. Testis-specific serine kinase 3 (Tssk3) is a conserved gene, but TSSK3 kinase functions and phosphorylation substrates of TSSK3 are not known.

OBJECTIVE

The goals of our studies were to understand the mechanism of action of TSSK3.

MATERIALS AND METHODS

We analyzed the localization of TSSK3 in sperm, used CRISPR/Cas9 to generate Tssk3 knockout (KO) mice in which nearly all of the Tssk3 open reading frame was deleted (ensuring it is a null mutation), analyzed the fertility of Tssk3 KO mice by breeding mice for 4 months, and conducted phosphoproteomics analysis of male testicular germ cells.

RESULTS

TSSK3 is expressed in elongating sperm and localizes to the sperm tail. To define the essential roles of TSSK3 in vivo, heterozygous (HET) or homozygous KO male mice were mated with wild-type females, and fertility was assessed over 4 months; Tssk3 KO males are sterile, whereas HET males produced normal litter sizes. The absence of TSSK3 results in disorganization of all stages of testicular seminiferous epithelium and significantly increased vacuolization of germ cells, leading to dramatically reduced sperm counts and abnormal sperm morphology; despite these histologic changes, Tssk3 null mice have normal testis size. To elucidate the mechanisms causing the KO phenotype, we conducted phosphoproteomics using purified germ cells from Tssk3 HET and KO testes. We found that proteins implicated in male infertility, such as GAPDHS, ACTL7A, ACTL9, and REEP6, showed significantly reduced phosphorylation in KO testes compared to HET testes, despite unaltered total protein levels.

CONCLUSIONS

We demonstrated that TSSK3 is essential for male fertility and crucial for phosphorylation of multiple infertility-related proteins. These studies and the pathways in which TSSK3 functions have implications for human male infertility and nonhormonal contraception.

New insights into activation and function of the AMPK

The classical role of AMP-activated protein kinase (AMPK) is as a cellular energy sensor activated by falling energy status, signalled by increases in AMP to ATP and ADP to ATP ratios. Once activated, AMPK acts to restore energy homeostasis by promoting ATP-producing catabolic pathways while inhibiting energy-consuming processes. In this Review, we provide an update on this canonical (AMP/ADP-dependent) activation mechanism, but focus mainly on recently described non-canonical pathways, including those by which AMPK senses the availability of glucose, glycogen or fatty acids and by which it senses damage to lysosomes and nuclear DNA. We also discuss new findings on the regulation of carbohydrate and lipid metabolism, mitochondrial and lysosomal homeostasis, and DNA repair. Finally, we discuss the role of AMPK in cancer, obesity, diabetes, nonalcoholic steatohepatitis (NASH) and other disorders where therapeutic targeting may exert beneficial effects.

Cold Storage Followed by Transplantation Induces Interferon-Gamma and STAT-1 in Kidney Grafts

Cold storage (CS)-mediated inflammation, a reality of donor kidney processing and transplantation, can contribute to organ graft failure. However, the mechanisms by which this inflammation is perpetuated during and after CS remain unclear. Here, we examined the immunoregulatory roles of signal transducer and activator of transcription (STAT) family proteins, most notably STAT1 and STAT3, with our in vivo model of renal CS and transplant. Donor rat kidneys were exposed to 4 h or 18 h of CS, which was then followed by transplantation (CS + transplant). STAT total protein level and activity (phosphorylation) were evaluated via Western blot analysis and mRNA expression was tabulated using quantitative RT-PCR after organ harvest on day 1 or day 9 post-surgery. In vivo assays were further corroborated via similar analyses featuring in vitro models, specifically proximal tubular cells (human and rat) as well as macrophage cells (Raw 264.7). Strikingly, gene expression of IFN-γ (a pro-inflammatory cytokine inducer of STAT) and STAT1 were markedly increased after CS + transplant. STAT3 dephosphorylation was additionally observed after CS, a result suggestive of dysregulation of anti-inflammatory signaling as phosphorylated STAT3 acts as a transcription factor in the nucleus to increase the expression of anti-inflammatory signaling molecules. In vitro, IFN-γ gene expression as well as amplification of downstream STAT1 and inducible nitric oxide synthase (iNOS; a hallmark of ischemia reperfusion injury) was remarkably increased after CS + rewarming. Collectively, these results demonstrate that aberrant induction of STAT1 is sustained in vivo post-CS exposure and post-transplant. Thus, Jak/STAT signaling may be a viable therapeutic target during CS to mitigate poor graft outcomes when transplanting kidneys from deceased donors.

The Role of Mitophagy in Skeletal Muscle Damage and Regeneration

Mitochondria are cellular organelles that play an essential role in generating the chemical energy needed for the biochemical reactions in cells. Mitochondrial biogenesis, i.e., de novo mitochondria formation, results in enhanced cellular respiration, metabolic processes, and ATP generation, while autophagic clearance of mitochondria (mitophagy) is required to remove damaged or useless mitochondria. The balance between the opposing processes of mitochondrial biogenesis and mitophagy is highly regulated and crucial for the maintenance of the number and function of mitochondria as well as for the cellular homeostasis and adaptations to metabolic demands and extracellular stimuli. In skeletal muscle, mitochondria are essential for maintaining energy homeostasis, and the mitochondrial network exhibits complex behaviors and undergoes dynamic remodeling in response to various conditions and pathologies characterized by changes in muscle cell structure and metabolism, such as exercise, muscle damage, and myopathies. In particular, the involvement of mitochondrial remodeling in mediating skeletal muscle regeneration following damage has received increased attention, as modifications in mitophagy-related signals arise from exercise, while variations in mitochondrial restructuring pathways can lead to partial regeneration and impaired muscle function. Muscle regeneration (through myogenesis) following exercise-induced damage is characterized by a highly regulated, rapid turnover of poor-functioning mitochondria, permitting the synthesis of better-functioning mitochondria to occur. Nevertheless, essential aspects of mitochondrial remodeling during muscle regeneration remain poorly understood and warrant further characterization. In this review, we focus on the critical role of mitophagy for proper muscle cell regeneration following damage, highlighting the molecular mechanisms of the mitophagy-associated mitochondrial dynamics and network reformation.

TRAF3: A novel regulator of mitochondrial physiology and metabolic pathways in B lymphocytes

Mitochondria, the organelle critical for cell survival and metabolism, are exploited by cancer cells and provide an important therapeutic target in cancers. Mitochondria dynamically undergo fission and fusion to maintain their diverse functions. Proteins controlling mitochondrial fission and fusion have been recognized as essential regulators of mitochondrial functions, mitochondrial quality control, and cell survival. In a recent proteomic study, we identified the key mitochondrial fission factor, MFF, as a new interacting protein of TRAF3, a known tumor suppressor of multiple myeloma and other B cell malignancies. This interaction recruits the majority of cytoplasmic TRAF3 to mitochondria, allowing TRAF3 to regulate mitochondrial morphology, mitochondrial functions, and mitochondria-dependent apoptosis in resting B lymphocytes. Interestingly, recent transcriptomic, metabolic and lipidomic studies have revealed that TRAF3 also vitally regulates multiple metabolic pathways in B cells, including phospholipid metabolism, glucose metabolism, and ribonucleotide metabolism. Thus, TRAF3 emerges as a novel regulator of mitochondrial physiology and metabolic pathways in B lymphocytes and B cell malignancies. Here we review current knowledge in this area and discuss relevant clinical implications.

Targeting CRL4 suppresses chemoresistant ovarian cancer growth by inducing mitophagy

Chemoresistance has long been the bottleneck of ovarian cancer (OC) prognosis. It has been shown that mitochondria play a crucial role in cell response to chemotherapy and that dysregulated mitochondrial dynamics is intricately linked with diseases like OC, but the underlying mechanisms remain equivocal. Here, we demonstrate a new mechanism where CRL4^CUL4A/DDB1 manipulates OC cell chemoresistance by regulating mitochondrial dynamics and mitophagy. CRL4^CUL4A/DDB1 depletion enhanced mitochondrial fission by upregulating AMPKα^Thr172 and MFF^{Ser172/Ser146} phosphorylation, which in turn recruited DRP1 to mitochondria. CRL4^CUL4A/DDB1 loss stimulated mitophagy through the Parkin-PINK1 pathway to degrade the dysfunctional and fragmented mitochondria. Importantly, CRL4^CUL4A/DDB1 loss inhibited OC cell proliferation, whereas inhibiting autophagy partially reversed this disruption. Our findings provide novel insight into the multifaceted function of the CRL4 E3 ubiquitin ligase complex in regulating mitochondrial fission, mitophagy, and OC chemoresistance. Disruption of CRL4^CUL4A/DDB1 and mitophagy may be a promising therapeutic strategy to overcome chemoresistance in OC.

AMPK/MFF Activation: Role in Mitochondrial Fission and Mitophagy in Dry Eye

Purpose

To assess the role of mitochondrial morphology and adenosine monophosphate-activated protein kinase (AMPK)/mitochondrial fission factor (MFF) in dry eye and the underlying mechanisms.

Methods

Immortalized human corneal epithelial cells (HCECs) and primary HCECs were cultured under high osmotic pressure (HOP). C57BL/6 female mice were injected subcutaneously with scopolamine. Quantitative real-time PCR was used to measure mRNA expression. Protein expression was assessed by western blot and immunofluorescence staining. Mitochondrial morphology was observed by confocal microscopy and transmission electron microscopy.

Results

First, HOP induced mitochondrial oxidative damage to HCECs, accompanied by mitochondrial fission and increased mitophagy. Then, AMPK/MFF pathway proteins were increased consequent to HOP-induced energy metabolism dysfunction. Interestingly, the AMPK pathway promoted mitochondrial fission and mitophagy by increasing the recruitment of dynamin-related protein 1 (DRP1) to the mitochondrial outer membrane in the HOP group. Moreover, AMPK knockdown attenuated mitochondrial fission and mitophagy due to HOP in HCECs. AMPK activation triggered mitochondrial fission and mitophagy. Mitochondrial fission of HCECs stressed by HOP was mediated via MFF phosphorylation. MFF knockdown reversed mitochondrial fragmentation and mitophagy in HCECs treated with HOP. Inhibition of MFF protected HCECs against oxidative damage, cell death, and inflammation in the presence of HOP. Finally, we detected mitochondrial fission and AMPK pathway activation in vivo.

Conclusions

The AMPK/MFF pathway mediates the development of dry eye by positively regulating mitochondrial fission and mitophagy. Inhibition of mitochondrial fission can alleviate oxidative damage and inflammation in dry eye and may provide experimental evidence for treating dry eye.

AMPK signaling and its targeting in cancer progression and treatment

The intrinsic mechanisms sensing the imbalance of energy in cells are pivotal for cell survival under various environmental insults. AMP-activated protein kinase (AMPK) serves as a central guardian maintaining energy homeostasis by orchestrating diverse cellular processes, such as lipogenesis, glycolysis, TCA cycle, cell cycle progression and mitochondrial dynamics. Given that AMPK plays an essential role in the maintenance of energy balance and metabolism, managing AMPK activation is considered as a promising strategy for the treatment of metabolic disorders such as type 2 diabetes and obesity. Since AMPK has been attributed to aberrant activation of metabolic pathways, mitochondrial dynamics and functions, and epigenetic regulation, which are hallmarks of cancer, targeting AMPK may open up a new avenue for cancer therapies. Although AMPK is previously thought to be involved in tumor suppression, several recent studies have unraveled its tumor promoting activity. The double-edged sword characteristics for AMPK as a tumor suppressor or an oncogene are determined by distinct cellular contexts. In this review, we will summarize recent progress in dissecting the upstream regulators and downstream effectors for AMPK, discuss the distinct roles of AMPK in cancer regulation and finally offer potential strategies with AMPK targeting in cancer therapy.

Aβ42 oligomers trigger synaptic loss through CAMKK2-AMPK-dependent effectors coordinating mitochondrial fission and mitophagy

During the early stages of Alzheimer's disease (AD) in both mouse models and human patients, soluble forms of Amyloid-β 1-42 oligomers (Aβ42o) trigger loss of excitatory synapses (synaptotoxicity) in cortical and hippocampal pyramidal neurons (PNs) prior to the formation of insoluble amyloid plaques. In a transgenic AD mouse model, we observed a spatially restricted structural remodeling of mitochondria in the apical tufts of CA1 PNs dendrites corresponding to the dendritic domain where the earliest synaptic loss is detected in vivo. We also observed AMPK over-activation as well as increased fragmentation and loss of mitochondrial biomass in Ngn2-induced neurons derived from a new APP^Swe/Swe knockin human ES cell line. We demonstrate that Aβ42o-dependent over-activation of the CAMKK2-AMPK kinase dyad mediates synaptic loss through coordinated phosphorylation of MFF-dependent mitochondrial fission and ULK2-dependent mitophagy. Our results uncover a unifying stress-response pathway causally linking Aβ42o-dependent structural remodeling of dendritic mitochondria to synaptic loss.

Opposing effects on regulated insulin secretion of acute vs chronic stimulation of AMP-activated protein kinase

AIMS/HYPOTHESIS

Although targeted in extrapancreatic tissues by several drugs used to treat type 2 diabetes, the role of AMP-activated protein kinase (AMPK) in the control of insulin secretion is still debatable. Previous studies have used pharmacological activators of limited selectivity and specificity, and none has examined in primary pancreatic beta cells the actions of the latest generation of highly potent and specific activators that act via the allosteric drug and metabolite (ADaM) site.

METHODS

AMPK was activated acutely in islets isolated from C57BL6/J mice, and in an EndoC-βH3 cell line, using three structurally distinct ADaM site activators (991, PF-06409577 and RA089), with varying selectivity for β1- vs β2-containing complexes. Mouse lines expressing a gain-of-function mutation in the γ1 AMPK subunit (D316a) were generated to examine the effects of chronic AMPK stimulation in the whole body, or selectively in the beta cell.

RESULTS

Acute (1.5 h) treatment of wild-type mouse islets with 991, PF-06409577 or RA089 robustly stimulated insulin secretion at high glucose concentrations (p<0.01, p<0.05 and p<0.001, respectively), despite a lowering of glucose-induced intracellular free Ca2+ dynamics in response to 991 (AUC, p<0.05) and to RA089 at the highest dose (25 μmol/l) at 5.59 min (p<0.05). Although abolished in the absence of AMPK, the effects of 991 were observed in the absence of the upstream kinase, liver kinase B1, further implicating 'amplifying' pathways. In marked contrast, chronic activation of AMPK, either globally or selectively in the beta cell, achieved using a gain-of-function mutant, impaired insulin release in vivo (p<0.05 at 15 min following i.p. injection of 3 mmol/l glucose) and in vitro (p<0.01 following incubation of islets with 17 mmol/l glucose), and lowered glucose tolerance (p<0.001).

CONCLUSIONS/INTERPRETATION

AMPK activation exerts complex, time-dependent effects on insulin secretion. These observations should inform the design and future clinical use of AMPK modulators.

Mitochondrial Dysfunction in Cardiovascular Diseases: Potential Targets for Treatment

Cardiovascular diseases (CVDs) are serious public health issues and are responsible for nearly one-third of global deaths. Mitochondrial dysfunction is accountable for the development of most CVDs. Mitochondria produce adenosine triphosphate through oxidative phosphorylation and inevitably generate reactive oxygen species (ROS). Excessive ROS causes mitochondrial dysfunction and cell death. Mitochondria can protect against these damages via the regulation of mitochondrial homeostasis. In recent years, mitochondria-targeted therapy for CVDs has attracted increasing attention. Various studies have confirmed that clinical drugs (β-blockers, angiotensin-converting enzyme inhibitors/angiotensin receptor-II blockers) against CVDs have mitochondrial protective functions. An increasing number of cardiac mitochondrial targets have shown their cardioprotective effects in experimental and clinical studies. Here, we briefly introduce the mechanisms of mitochondrial dysfunction and summarize the progression of mitochondrial targets against CVDs, which may provide ideas for experimental studies and clinical trials.

Blocking exosomal secretion aggravates 1,4-Benzoquinone-induced mitochondrial fission activated by the AMPK/MFF/Drp1 pathway in HL-60 cells

There is in vivo and in vitro evidence that exposure to benzene or its metabolites could affect the mitochondrial function. However, the underlying molecular mechanism of mitochondrial damage remains to be elucidated. In this study, exposure of human promyelocytic leukemia cells (HL-60) to 1,4-benzoquinone (1,4-BQ; an active metabolite of benzene) increased the intracellular reactive oxygen species levels, decreased the mitochondrial membrane potential, adenosine triphosphate production and mitochondrial DNA (mtDNA) copy number, up-regulated the expression of mitochondrial fission proteins Drp1 and Fis1, and down-regulated the expression of mitochondrial fusion proteins Mfn2 and Opa1. Further study showed that 1,4-BQ mediated mitochondrial fission through activation of the AMP-activated protein kinase/mitochondrial fission factor/dynamin-related protein 1 pathway. Additionally, we also examined the role of exosomal secretion in mitochondrial damage under 1,4-BQ treatment. Results showed that 1,4-BQ increased the total protein level and mtDNA content in exosomes. Upon pre-treatment with the mitochondria-targeted antioxidant SS-31, there was attenuation of the mitochondrial damage induced by 1,4-BQ, accompanied by a change in the exosome release characteristics, while inhibition of exosomal secretion using GW4869 aggravated the 1,4-BQ-mediated mitochondrial fission. We concluded that exosomal secretion may serve as a self-protective mechanism of cells against 1,4-BQ-induced mitochondria damage and mitochondrial dynamics interference.

The Interplay between Cell-Extracellular Matrix Interaction and Mitochondria Dynamics in Cancer

The tumor microenvironment, in particular the extracellular matrix (ECM), plays a pivotal role in controlling tumor initiation and progression. In particular, the interaction between cancer cells and the ECM promotes cancer cell growth and invasion, leading to the formation of distant metastasis. Alterations in cancer cell metabolism is a key hallmark of cancer, which is often associated with alterations in mitochondrial dynamics. Recent research highlighted that, changes in mitochondrial dynamics are associated with cancer migration and metastasis-these has been extensively reviewed elsewhere. However, less is known about the interplay between the extracellular matrix and mitochondria functions. In this review, we will highlight how ECM remodeling associated with tumorigenesis contribute to the regulation of mitochondrial function, ultimately promoting cancer cell metabolic plasticity, able to fuel cancer invasion and metastasis.

Mitochondrial Quality Surveillance: Mitophagy in cardiovascular health and disease

Selective autophagy of mitochondria, known as mitophagy, is a major quality control pathway in the heart that is involved in removing unwanted or dysfunctional mitochondria from the cell. Baseline mitophagy is critical for maintaining fitness of the mitochondrial network by continuous turnover of aged and less-functional mitochondria. Mitophagy is also critical in adapting to stress associated with mitochondrial damage or dysfunction. The removal of damaged mitochondria prevents reactive oxygen species-mediated damage to proteins and DNA and suppresses activation of inflammation and cell death. Impairments in mitophagy are associated with the pathogenesis of many diseases, including cancers, inflammatory diseases, neurodegeneration, and cardiovascular disease. Mitophagy is a highly regulated and complex process that requires the coordination of labeling dysfunctional mitochondria for degradation while simultaneously promoting de novo autophagosome biogenesis adjacent to the cargo. In this review, we provide an update on our current understanding of these steps in mitophagy induction and discuss the physiological and pathophysiological consequences of altered mitophagy in the heart.

The Imbalance of Mitochondrial Fusion/Fission Drives High-Glucose-Induced Vascular Injury

Emerging evidence shows that mitochondria fusion/fission imbalance is related to the occurrence of hyperglycemia-induced vascular injury. To study the temporal dynamics of mitochondrial fusion and fission, we observed the alteration of mitochondrial fusion/fission proteins in a set of different high-glucose exposure durations, especially in the early stage of hyperglycemia. The in vitro results show that persistent cellular apoptosis and endothelial dysfunction can be induced rapidly within 12 hours’ high-glucose pre-incubation. Our results show that mitochondria maintain normal morphology and function within 4 hours’ high-glucose pre-incubation; with the extended high-glucose exposure, there is a transition to progressive fragmentation; once severe mitochondria fusion/fission imbalance occurs, persistent cellular apoptosis will develop. In vitro and in vivo results consistently suggest that mitochondrial fusion/fission homeostasis alterations trigger high-glucose-induced vascular injury. As the guardian of mitochondria, AMPK is suppressed in response to hyperglycemia, resulting in imbalanced mitochondrial fusion/fission, which can be reversed by AMPK stimulation. Our results suggest that mitochondrial fusion/fission’s staged homeostasis may be a predictive factor of diabetic cardiovascular complications.

Mitochondrial Fission Factor Is a Novel Interacting Protein of the Critical B Cell Survival Regulator TRAF3 in B Lymphocytes

Proteins controlling mitochondrial fission have been recognized as essential regulators of mitochondrial functions, mitochondrial quality control and cell apoptosis. In the present study, we identified the critical B cell survival regulator TRAF3 as a novel binding partner of the key mitochondrial fission factor, MFF, in B lymphocytes. Elicited by our unexpected finding that the majority of cytoplasmic TRAF3 proteins were localized at the mitochondria in resting splenic B cells after ex vivo culture for 2 days, we found that TRAF3 specifically interacted with MFF as demonstrated by co-immunoprecipitation and GST pull-down assays. We further found that in the absence of stimulation, increased protein levels of mitochondrial TRAF3 were associated with altered mitochondrial morphology, decreased mitochondrial respiration, increased mitochondrial ROS production and membrane permeabilization, which eventually culminated in mitochondria-dependent apoptosis in resting B cells. Loss of TRAF3 had the opposite effects on the morphology and function of mitochondria as well as mitochondria-dependent apoptosis in resting B cells. Interestingly, co-expression of TRAF3 and MFF resulted in decreased phosphorylation and ubiquitination of MFF as well as decreased ubiquitination of TRAF3. Moreover, lentivirus-mediated overexpression of MFF restored mitochondria-dependent apoptosis in TRAF3-deficient malignant B cells. Taken together, our findings provide novel insights into the apoptosis-inducing mechanisms of TRAF3 in B cells: as a result of survival factor deprivation or under other types of stress, TRAF3 is mobilized to the mitochondria through its interaction with MFF, where it triggers mitochondria-dependent apoptosis. This new role of TRAF3 in controlling mitochondrial homeostasis might have key implications in TRAF3-mediated regulation of B cell transformation in different cellular contexts. Our findings also suggest that mitochondrial fission is an actionable therapeutic target in human B cell malignancies, including those with TRAF3 deletion or relevant mutations.

Chronic Activation of AMPK Induces Mitochondrial Biogenesis through Differential Phosphorylation and Abundance of Mitochondrial Proteins in Dictyostelium discoideum

Mitochondrial biogenesis is a highly controlled process that depends on diverse signalling pathways responding to cellular and environmental signals. AMP-activated protein kinase (AMPK) is a critical metabolic enzyme that acts at a central control point in cellular energy homeostasis. Numerous studies have revealed the crucial roles of AMPK in the regulation of mitochondrial biogenesis; however, molecular mechanisms underlying this process are still largely unknown. Previously, we have shown that, in cellular slime mould Dictyostelium discoideum, the overexpression of the catalytic α subunit of AMPK led to enhanced mitochondrial biogenesis, which was accompanied by reduced cell growth and aberrant development. Here, we applied mass spectrometry-based proteomics of Dictyostelium mitochondria to determine the impact of chronically active AMPKα on the phosphorylation state and abundance of mitochondrial proteins and to identify potential protein targets leading to the biogenesis of mitochondria. Our results demonstrate that enhanced mitochondrial biogenesis is associated with variations in the phosphorylation levels and abundance of proteins related to energy metabolism, protein synthesis, transport, inner membrane biogenesis, and cellular signalling. The observed changes are accompanied by elevated mitochondrial respiratory activity in the AMPK overexpression strain. Our work is the first study reporting on the global phosphoproteome profiling of D. discoideum mitochondria and its changes as a response to constitutively active AMPK. We also propose an interplay between the AMPK and mTORC1 signalling pathways in controlling the cellular growth and biogenesis of mitochondria in Dictyostelium as a model organism.

Mitochondrial Dynamics: A Potential Therapeutic Target for Ischemic Stroke

Stroke is one of the leading causes of death and disability worldwide. Brain injury after ischemic stroke involves multiple pathophysiological mechanisms, such as oxidative stress, mitochondrial dysfunction, excitotoxicity, calcium overload, neuroinflammation, neuronal apoptosis, and blood-brain barrier (BBB) disruption. All of these factors are associated with dysfunctional energy metabolism after stroke. Mitochondria are organelles that provide adenosine triphosphate (ATP) to the cell through oxidative phosphorylation. Mitochondrial dynamics means that the mitochondria are constantly changing and that they maintain the normal physiological functions of the cell through continuous division and fusion. Mitochondrial dynamics are closely associated with various pathophysiological mechanisms of post-stroke brain injury. In this review, we will discuss the role of the molecular mechanisms of mitochondrial dynamics in energy metabolism after ischemic stroke, as well as new strategies to restore energy homeostasis and neural function. Through this, we hope to uncover new therapeutic targets for the treatment of ischemic stroke.

Autophagy and Mitochondrial Homeostasis During Infection: A Double-Edged Sword

Autophagy, an essential biological process that affects immunity, is a powerful tool that host cells can use to defend against infections caused by pathogenic microorganisms. Autophagy can not only initiate innate immune responses but also degrade the cellular components that provide the conditions for removing the invaders. However, hyperactivated or inhibited autophagy leads to mitochondrial dysfunction, which is harmful to the host itself and is involved in many types of diseases. Mitochondria perform the functions of biological oxidation and energy exchange. In addition, mitochondrial functions are closely related to cell death, oxygen radical formation, and disease. Accumulation of mitochondrial metabolites affects survival of intracellular pathogens. In this mini-review, we focus on the crosstalk between autophagy and mitochondrial homeostasis during infection.

AMPK: restoring metabolic homeostasis over space and time

The evolution of AMPK and its homologs enabled exquisite responsivity and control of cellular energetic homeostasis. Recent work has been critical in establishing the mechanisms that determine AMPK activity, novel targets of AMPK action, and the distribution of AMPK-mediated control networks across the cellular landscape. The role of AMPK as a hub of metabolic control has led to intense interest in pharmacologic activation as a therapeutic avenue for a number of disease states, including obesity, diabetes, and cancer. As such, critical work on the compartmentalization of AMPK, its downstream targets, and the systems it influences has progressed in recent years. The variegated distribution of AMPK-mediated control of metabolic homeostasis has revealed key insights into AMPK in normal biology and future directions for AMPK-based therapeutic strategies.

Inositol serves as a natural inhibitor of mitochondrial fission by directly targeting AMPK

Mitochondrial dynamics regulated by mitochondrial fusion and fission maintain mitochondrial functions, whose alterations underline various human diseases. Here, we show that inositol is a critical metabolite directly restricting AMPK-dependent mitochondrial fission independently of its classical mode as a precursor for phosphoinositide generation. Inositol decline by IMPA1/2 deficiency elicits AMPK activation and mitochondrial fission without affecting ATP level, whereas inositol accumulation prevents AMPK-dependent mitochondrial fission. Metabolic stress or mitochondrial damage causes inositol decline in cells and mice to elicit AMPK-dependent mitochondrial fission. Inositol directly binds to AMPKγ and competes with AMP for AMPKγ binding, leading to restriction of AMPK activation and mitochondrial fission. Our study suggests that the AMP/inositol ratio is a critical determinant for AMPK activation and establishes a model in which AMPK activation requires inositol decline to release AMPKγ for AMP binding. Hence, AMPK is an inositol sensor, whose inactivation by inositol serves as a mechanism to restrict mitochondrial fission.

Phosphorylated cingulin localises GEF-H1 at tight junctions to protect vascular barriers in blood endothelial cells

Dysfunction of vascular barriers is a critical step in inflammatory diseases. Endothelial tight junctions (TJs) control barrier function, and the cytoplasmic adaptor protein cingulin connects TJs to signalling pathways. However, local events at TJs during inflammation are largely unknown. In this study, we investigate the local response of TJ adaptor protein cingulin and its interaction with Rho guanine nucleotide exchange factor H1 (GEF-H1, also known as ARHGEF2) upon vascular barrier disruption to find a new approach to counteract vascular leak. Based on transendothelial-electrical-resistance (TEER) measurements, cingulin strengthened barrier integrity upon stimulation with histamine, thrombin and VEGF. Cingulin also attenuated myosin light chain 2 (MLC2; also known as MYL2) phosphorylation by localising GEF-H1 to cell junctions. By using cingulin phosphomutants, we verified that the phosphorylation of the cingulin head domain is required for its protective effect. Increased colocalisation of GEF-H1 and cingulin was observed in the vessels of vasculitis patients compared to those in healthy skin. Our findings demonstrate that cingulin can counteract vascular leak at TJs, suggesting the existence of a novel mechanism in blood endothelial cells that protects barrier function during disease.

Summary: Vascular leak in response to histamine, thrombin and VEGF can be counteracted by AMPK phosphorylating cingulin at its head domain. Consequential binding of GEF-H1 to tight junctions protects vascular barrier function.

Mitophagy Regulates Neurodegenerative Diseases

Mitochondria play an essential role in supplying energy for the health and survival of neurons. Mitophagy is a metabolic process that removes dysfunctional or redundant mitochondria. This process preserves mitochondrial health. However, defective mitophagy triggers the accumulation of damaged mitochondria, causing major neurodegenerative disorders. This review introduces molecular mechanisms and signaling pathways behind mitophagy regulation. Furthermore, we focus on the recent advances in understanding the potential role of mitophagy in the pathogenesis of major neurodegenerative diseases (Parkinson's, Alzheimer's, Huntington's, etc.) and aging. The findings will help identify the potential interventions of mitophagy regulation and treatment strategies of neurodegenerative diseases.

Novel Insights and Current Evidence for Mechanisms of Atherosclerosis: Mitochondrial Dynamics as a Potential Therapeutic Target

Cardiovascular disease (CVD) is the main cause of death worldwide. Atherosclerosis is the underlying pathological basis of CVD. Mitochondrial homeostasis is maintained through the dynamic processes of fusion and fission. Mitochondria are involved in many cellular processes, such as steroid biosynthesis, calcium homeostasis, immune cell activation, redox signaling, apoptosis, and inflammation, among others. Under stress conditions, mitochondrial dynamics, mitochondrial cristae remodeling, and mitochondrial ROS (mitoROS) production increase, mitochondrial membrane potential (MMP) decreases, calcium homeostasis is imbalanced, and mitochondrial permeability transition pore open (mPTP) and release of mitochondrial DNA (mtDNA) are activated. mtDNA recognized by TLR9 can lead to NF-κB pathway activation and pro-inflammatory factor expression. At the same time, TLR9 can also activate NLRP3 inflammasomes and release interleukin, an event that eventually leads to tissue damage and inflammatory responses. In addition, mitochondrial dysfunction may amplify the activation of NLRP3 through the production of mitochondrial ROS, which together aggravate accumulating mitochondrial damage. In addition, mtDNA defects or gene mutation can lead to mitochondrial oxidative stress. Finally, obesity, diabetes, hypertension and aging are risk factors for the progression of CVD, which are closely related to mitochondrial dynamics. Mitochondrial dynamics may represent a new target in the treatment of atherosclerosis. Antioxidants, mitochondrial inhibitors, and various new therapies to correct mitochondrial dysfunction represent a few directions for future research on therapeutic intervention and amelioration of atherosclerosis.

The influence of aerobic exercise on mitochondrial quality control in skeletal muscle

Mitochondria are dynamic organelles, intricately designed to meet cellular energy requirements. To accommodate alterations in energy demand, mitochondria have a high degree of plasticity, changing in response to transient activation of numerous stress-related pathways. This adaptive response is particularly relevant in highly metabolic tissues such as skeletal muscle, where mitochondria support numerous biological processes related to metabolism, growth and regeneration. Aerobic exercise is a potent stimulus for skeletal muscle remodelling, leading to alterations in substrate utilisation, fibre-type composition and performance. Underlying these physiological responses is a change in mitochondrial quality control (MQC), a term encompassing the co-ordination of mitochondrial synthesis (biogenesis), remodelling (dynamics) and degradation (mitophagy) pathways. Understanding of MQC in skeletal muscle and the regulatory role of aerobic exercise of this process are rapidly advancing, as are the molecular techniques allowing the study of MQC in vivo. Given the emerging link between MQC and the onset of numerous non-communicable diseases, understanding the molecular regulation of MQC, and the role of aerobic exercise in this process, will have substantial future impact on therapeutic approaches to manipulate MQC and maintain mitochondrial function across health span.

AMPK and Pulmonary Hypertension: Crossroads Between Vasoconstriction and Vascular Remodeling

Pulmonary hypertension (PH) is a debilitating and life-threatening disease characterized by increased blood pressure within the pulmonary arteries. Adenosine monophosphate-activated protein kinase (AMPK) is a heterotrimeric serine-threonine kinase that contributes to the regulation of metabolic and redox signaling pathways. It has key roles in the regulation of cell survival and proliferation. The role of AMPK in PH is controversial because both inhibition and activation of AMPK are preventive against PH development. Some clinical studies found that metformin, the first-line antidiabetic drug and the canonical AMPK activator, has therapeutic efficacy during treatment of early-stage PH. Other study findings suggest the use of metformin is preferentially beneficial for treatment of PH associated with heart failure with preserved ejection fraction (PH-HFpEF). In this review, we discuss the "AMPK paradox" and highlight the differential effects of AMPK on pulmonary vasoconstriction and pulmonary vascular remodeling. We also review the effects of AMPK activators and inhibitors on rescue of preexisting PH in animals and include a discussion of gender differences in the response to metformin in PH.

Mitochondrial network remodeling: an important feature of myogenesis and skeletal muscle regeneration

The remodeling of the mitochondrial network is a critical process in maintaining cellular homeostasis and is intimately related to mitochondrial function. The interplay between the formation of new mitochondria (biogenesis) and the removal of damaged mitochondria (mitophagy) provide a means for the repopulation of the mitochondrial network. Additionally, mitochondrial fission and fusion serve as a bridge between biogenesis and mitophagy. In recent years, the importance of these processes has been characterised in multiple tissue- and cell-types, and under various conditions. In skeletal muscle, the robust remodeling of the mitochondrial network is observed, particularly after injury where large portions of the tissue/cell structures are damaged. The significance of mitochondrial remodeling in regulating skeletal muscle regeneration has been widely studied, with alterations in mitochondrial remodeling processes leading to incomplete regeneration and impaired skeletal muscle function. Needless to say, important questions related to mitochondrial remodeling and skeletal muscle regeneration still remain unanswered and require further investigation. Therefore, this review will discuss the known molecular mechanisms of mitochondrial network remodeling, as well as integrate these mechanisms and discuss their relevance in myogenesis and regenerating skeletal muscle.

Genetic Neuropathy Due to Impairments in Mitochondrial Dynamics

Mitochondria are dynamic organelles capable of fusing, dividing, and moving about the cell. These properties are especially important in neurons, which in addition to high energy demand, have unique morphological properties with long axons. Notably, mitochondrial dysfunction causes a variety of neurological disorders including peripheral neuropathy, which is linked to impaired mitochondrial dynamics. Nonetheless, exactly why peripheral neurons are especially sensitive to impaired mitochondrial dynamics remains somewhat enigmatic. Although the prevailing view is that longer peripheral nerves are more sensitive to the loss of mitochondrial motility, this explanation is insufficient. Here, we review pathogenic variants in proteins mediating mitochondrial fusion, fission and transport that cause peripheral neuropathy. In addition to highlighting other dynamic processes that are impacted in peripheral neuropathies, we focus on impaired mitochondrial quality control as a potential unifying theme for why mitochondrial dysfunction and impairments in mitochondrial dynamics in particular cause peripheral neuropathy.

AMPK-dependent phosphorylation is required for transcriptional activation of TFEB and TFE3

Increased macroautophagy/autophagy and lysosomal activity promote tumor growth, survival and chemo-resistance. During acute starvation, autophagy is rapidly engaged by AMPK (AMP-activated protein kinase) activation and MTOR (mechanistic target of rapamycin kinase) complex 1 (MTORC1) inhibition to maintain energy homeostasis and cell survival. TFEB (transcription factor E3) and TFE3 (transcription factor binding to IGHM enhancer 3) are master transcriptional regulators of autophagy and lysosomal activity and their cytoplasm/nuclear shuttling is controlled by MTORC1-dependent multisite phosphorylation. However, it is not known whether and how the transcriptional activity of TFEB or TFE3 is regulated. We show that AMPK mediates phosphorylation of TFEB and TFE3 on three serine residues, leading to TFEB and TFE3 transcriptional activity upon nutrient starvation, FLCN (folliculin) depletion and pharmacological manipulation of MTORC1 or AMPK. Collectively, we show that MTORC1 specifically controls TFEB and TFE3 cytosolic retention, whereas AMPK is essential for TFEB and TFE3 transcriptional activity. This dual and opposing regulation of TFEB and TFE3 by MTORC1 and AMPK is reminiscent of the regulation of another critical regulator of autophagy, ULK1 (unc-51 like autophagy activating kinase 1). Surprisingly, we show that chemoresistance is mediated by AMPK-dependent activation of TFEB, which is abolished by pharmacological inhibition of AMPK or mutation of serine 466, 467 and 469 to alanine residues within TFEB. Altogether, we show that AMPK is a key regulator of TFEB and TFE3 transcriptional activity, and we validate AMPK as a promising target in cancer therapy to evade chemotherapeutic resistance.AbbreviationsACACA: acetyl-CoA carboxylase alpha; ACTB: actin beta; AICAR: 5-aminoimidazole-4-carboxamide ribonucleotide; AMPK: AMP-activated protein kinase; AMPKi: AMPK inhibitor, SBI-0206965; CA: constitutively active; CARM1: coactivator-associated arginine methyltransferase 1; CFP: cyan fluorescent protein; CLEAR: coordinated lysosomal expression and regulation; DKO: double knock-out; DMEM: Dulbecco's modified Eagle's medium; DMSO: dimethyl sulfoxide; DQ-BSA: self-quenched BODIPY® dye conjugates of bovine serum albumin; EBSS: Earle's balanced salt solution; FLCN: folliculin; GFP: green fluorescent protein; GST: glutathione S-transferases; HD: Huntington disease; HTT: huntingtin; KO: knock-out; LAMP1: lysosomal associated membrane protein 1; MEF: mouse embryonic fibroblasts; MITF: melanocyte inducing transcription factor; MTORC1: MTOR complex 1; PolyQ: polyglutamine; RPS6: ribosomal protein S6; RT-qPCR: reverse transcription quantitative polymerase chain reaction; TCL: total cell lysates; TFE3: transcription factor binding to IGHM enhancer 3; TFEB: transcription factor EB; TKO: triple knock-out; ULK1: unc-51 like autophagy activating kinase 1.

Deletion of intestinal epithelial AMP-activated protein kinase alters distal colon permeability but not glucose homeostasis

Objective

The intestinal epithelial barrier (IEB) restricts the passage of microbes and potentially harmful substances from the lumen through the paracellular space, and rupture of its integrity is associated with a variety of gastrointestinal disorders and extra-digestive diseases. Increased IEB permeability has been linked to disruption of metabolic homeostasis leading to obesity and type 2 diabetes. Interestingly, recent studies have uncovered compelling evidence that the AMP-activated protein kinase (AMPK) signaling pathway plays an important role in maintaining epithelial cell barrier function. However, our understanding of the function of intestinal AMPK in regulating IEB and glucose homeostasis remains sparse.

Methods

We generated mice lacking the two α1 and α2 AMPK catalytic subunits specifically in intestinal epithelial cells (IEC AMPK KO) and determined the physiological consequences of intestinal-specific deletion of AMPK in response to high-fat diet (HFD)-induced obesity. We combined histological, functional, and integrative analyses to ascertain the effects of gut AMPK loss on intestinal permeability in vivo and ex vivo and on the development of obesity and metabolic dysfunction. We also determined the impact of intestinal AMPK deletion in an inducible mouse model (i-IEC AMPK KO) by measuring IEB function, glucose homeostasis, and the composition of gut microbiota via fecal 16S rRNA sequencing.

Results

While there were no differences in in vivo intestinal permeability in WT and IEC AMPK KO mice, ex vivo transcellular and paracellular permeability measured in Ussing chambers was significantly increased in the distal colon of IEC AMPK KO mice. This was associated with a reduction in pSer425 GIV phosphorylation, a marker of leaky gut barrier. However, the expression of tight junction proteins in intestinal epithelial cells and pro-inflammatory cytokines in the lamina propria were not different between genotypes. Although the HFD-fed AMPK KO mice displayed suppression of the stress polarity signaling pathway and a concomitant increase in colon permeability, loss of intestinal AMPK did not exacerbate body weight gain or adiposity. Deletion of AMPK was also not sufficient to alter glucose homeostasis or the acute glucose-lowering action of metformin in control diet (CD)- or HFD-fed mice. CD-fed i-IEC AMPK KO mice also presented higher permeability in the distal colon under homeostatic conditions but, surprisingly, this was not detected upon HFD feeding. Alteration in epithelial barrier function in the i-IEC AMPK KO mice was associated with a shift in the gut microbiota composition with higher levels of Clostridiales and Desulfovibrionales.

Conclusions

Altogether, our results revealed a significant role of intestinal AMPK in maintaining IEB integrity in the distal colon but not in regulating glucose homeostasis. Our data also highlight the complex interaction between gut microbiota and host AMPK.

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Deletion of intestinal AMPKα1 and α2 suppresses the stress-polarity signaling (SPS) pathway.

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Loss of the SPS pathway is associated with increased paracellular permeability in the distal colon.

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Intestinal AMPK is dispensable for the acute glucose-lowering action of metformin.

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Loss of intestinal AMPK alters the gut microbiota composition.

MAVS is energized by Mff which senses mitochondrial metabolism via AMPK for acute antiviral immunity

Mitochondria are multifunctional organelles that produce energy and are critical for various signaling pathways. Mitochondrial antiviral signaling (MAVS) is a mitochondrial outer membrane protein essential for the anti-RNA viral immune response, which is regulated by mitochondrial dynamics and energetics; however, the molecular link between mitochondrial metabolism and immunity is unclear. Here we show in cultured mammalian cells that MAVS is activated by mitochondrial fission factor (Mff), which senses mitochondrial energy status. Mff mediates the formation of active MAVS clusters on mitochondria, independent of mitochondrial fission and dynamin-related protein 1. Under mitochondrial dysfunction, Mff is phosphorylated by the cellular energy sensor AMP-activated protein kinase (AMPK), leading to the disorganization of MAVS clusters and repression of the acute antiviral response. Mff also contributes to immune tolerance during chronic infection by disrupting the mitochondrial MAVS clusters. Taken together, Mff has a critical function in MAVS-mediated innate immunity, by sensing mitochondrial energy metabolism via AMPK signaling.

The role of AMPK in metabolism and its influence on DNA damage repair

One of the most complex health disproportions in the human body is the metabolic syndrome (MetS). It can result in serious health consequences such as type 2 diabetes mellitus, atherosclerosis or insulin resistance. The center of energy regulation in human is AMP-activated protein kinase (AMPK), which modulates cells' metabolic pathways and protects them against negative effects of metabolic stress, e.g. reactive oxygen species. Moreover, recent studies show the relationship between the AMPK activity and the regulation of DNA damage repair such as base excision repair (BER) system, which is presented in relation to the influence of MetS on human genome. Hence, AMPK is studied not only in the field of counteracting MetS but also prevention of genetic alterations and cancer development. Through understanding AMPK pathways and its role in cells with damaged DNA it might be possible to improve cell's repair processes and develop new therapies. This review presents AMPK role in eukaryotic cells and focuses on the relationship between AMPK activity and the regulation of BER system through its main component-8-oxoguanine glycosylase (OGG1).

Mitochondrial Dynamics: Fission and Fusion in Fate Determination of Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are pivotal to tissue homeostasis, repair, and regeneration due to their potential for self-renewal, multilineage differentiation, and immune modulation. Mitochondria are highly dynamic organelles that maintain their morphology via continuous fission and fusion, also known as mitochondrial dynamics. MSCs undergo specific mitochondrial dynamics during proliferation, migration, differentiation, apoptosis, or aging. Emerging evidence suggests that mitochondrial dynamics are key contributors to stem cell fate determination. The coordination of mitochondrial fission and fusion is crucial for cellular function and stress responses, while abnormal fission and/or fusion causes MSC dysfunction. This review focuses on the role of mitochondrial dynamics in MSC commitment under physiological and stress conditions. We highlight mechanistic insights into modulating mitochondrial dynamics and mitochondrial strategies for stem cell-based regenerative medicine. These findings shed light on the contribution of mitochondrial dynamics to MSC fate and MSC-based tissue repair.

Quantitative In Vivo Proteomics of Metformin Response in Liver Reveals AMPK-Dependent and -Independent Signaling Networks

Metformin is the front-line treatment for type 2 diabetes worldwide. It acts via effects on glucose and lipid metabolism in metabolic tissues, leading to enhanced insulin sensitivity. Despite significant effort, the molecular basis for metformin response remains poorly understood, with a limited number of specific biochemical pathways studied to date. To broaden our understanding of hepatic metformin response, we combine phospho-protein enrichment in tissue from genetically engineered mice with a quantitative proteomics platform to enable the discovery and quantification of basophilic kinase substrates in vivo. We define proteins whose binding to 14-3-3 are acutely regulated by metformin treatment and/or loss of the serine/threonine kinase, LKB1. Inducible binding of 250 proteins following metformin treatment is observed, 44% of which proteins bind in a manner requiring LKB1. Beyond AMPK, metformin activates protein kinase D and MAPKAPK2 in an LKB1-independent manner, revealing additional kinases that may mediate aspects of metformin response. Deeper analysis uncovered substrates of AMPK in endocytosis and calcium homeostasis.