Suppression of endothelial PGC-1α is associated with hypoxia-induced endothelial dysfunction and provides a new therapeutic target in pulmonary arterial hypertension

Emerging insights into pulmonary hypertension: the potential role of mitochondrial dysfunction and redox homeostasis

Pulmonary hypertension (PH) is heterogeneous diseases that can lead to death due to progressive right heart failure. Emerging evidence suggests that, in addition to its role in ATP production, changes in mitochondrial play a central role in their pathogenesis, regulating integrated metabolic and signal transduction pathways. This review focuses on the basic principles of mitochondrial redox status in pulmonary vascular and right ventricular disorders, a series of dysfunctional processes including mitochondrial quality control (mitochondrial biogenesis, mitophagy, mitochondrial dynamics, mitochondrial unfolded protein response) and mitochondrial redox homeostasis. In addition, we will summarize how mitochondrial renewal and dynamic changes provide innovative insights for studying and evaluating PH. This will provide us with a clearer understanding of the initial signal transmission of mitochondria in PH, which would further improve our understanding of the pathogenesis of PH.

p16INK4a promoted progress of MCT induced pulmonary hypertension via maintaining redox balance and autophagy pathway

Pulmonary arterial hypertension (PAH) is a disease characterized by increased pulmonary vascular resistance and elevated pulmonary arterial pressure. Currently, pathogenesis of PAH remains poorly understood, and therapeutic options are limited. In this study, we aimed to explore role of p16INK4A (p16) in the development of PAH using mouse model induced by monocrotaline (MCT). We utilized p16 knockout mice to investigate protective effects on PAH pathophysiology. Histopathological analysis, Western blotting, and transcriptomic profiling revealed that p16 knockout significantly reduced pathological changes associated with MCT-induced PAH, including vascular remodeling and pulmonary fibrosis. These effects were correlated with enhanced autophagy and balanced oxidative stress response following p16 deletion. Transcriptome analysis indicated that the regulatory impact of p16 on autophagy and oxidative stress was primarily mediated through its modulation of oxidative phosphorylation and glutathione metabolic pathways. Our findings provide new insights in PAH pathogenesis and suggest that targeting p16 may offer novel therapeutic approach for treating PAH. These results highlighted that p16 could be a therapeutic target for modulating autophagy and oxidative stress in PAH, paving the way for future research in this area.

The impact of high altitude (hypobaric hypoxia) on insulin resistance in humans

Exposure to hypobaric hypoxia (high altitude) diminishes systemic tissue oxygenation. Tissue hypoxia induces insulin resistance and a metabolic switch that reduces oxidative phosphorylation and glucose storage while enhancing glycolysis. Similarly to hypobaric hypoxia, insulin resistance develops in normal humans undergoing normobaric hypoxia and in patients with obstructive sleep apnea. Following acute exposure to high altitude, insulin resistance returns to baseline values upon returning to sea level or when compensatory mechanisms restore tissue oxygenation. However, insulin resistance persists in subjects unable to achieve sufficient oxygen delivery to tissues. Likewise, long-term residents at high altitude develop persistent insulin resistance when compensatory mechanisms do not attain adequate tissue oxygenation. Among these subjects, insulin resistance may cause clinical complications, such as hypertriglyceridemia, reduced HDL-c, visceral obesity, metabolic dysfunction-associated steatotic liver disease, essential hypertension, type 2 diabetes, subclinical vascular injury, cardiovascular disease, and kidney disease. Impaired tissue oxygenation allows the stabilization of hypoxia-inducible factor-1 (HIF-1), a transcription factor that modulates the transcriptional activity of a number of genes to coordinate the physiological responses to tissue hypoxia. Among them, HIF-1 downregulates PPARG, that codes peroxisome proliferator-activated receptor-gamma (PPAR-γ) and PPARGCA, that codes PPAR-γ coactivator-1α, in order to enable insulin resistance and the metabolic switch from oxidative phosphorylation toward glycolysis.

The Impact of Modifiable Risk Factors on the Endothelial Cell Methylome and Cardiovascular Disease Development

Cardiovascular disease (CVD) is the most prevalent cause of mortality and morbidity in the Western world. A common underlying hallmark of CVD is the plaque-associated arterial thickening, termed atherosclerosis. Although the molecular mechanisms underlying the aetiology of atherosclerosis remain unknown, it is clear that both its development and progression are associated with significant changes in the pattern of DNA methylation within the vascular cell wall. The endothelium is the major regulator of vascular homeostasis, and endothelial cell dysfunction (ED) is considered an early marker for atherosclerosis. Thus, it is speculated that changes in DNA methylation within endothelial cells may, in part, be causal in ED, leading to atherosclerosis and CVD generally. This review will evaluate the extensive evidence that environmental risk factors, known to be associated with atherosclerosis, such as diabetes, metabolic disorder, smoking, hypertension and hypercholesterolaemia etc. can affect the methylome of the endothelium and consequently act to alter gene transcription and function. Further, the potential mechanisms whereby such risk factors might impact upon the activities and/or specificities of the epigenetic writers and erasers which determine the methylome [the DNA methyl transferases (DNMTs) and Ten Eleven translocases (TETs)] are considered here. Notably, the TET proteins are members of the 2-oxoglutarate-dependent dioxygenase superfamily which require molecular oxygen (O2) and α-ketoglutarate (α-KG) as substrates and iron-2+ (Fe II) as a cofactor. This renders their activities subject to modulation by hypoxia, metabolic flux and cellular redox. The potential significance of this, with respect to the impact of modifiable risk factors upon the activities of the TETs and the methylome of the endothelium is discussed.

The causes of pulmonary hypertension and the benefits of aerobic exercise for pulmonary hypertension from an integrated perspective

Pulmonary hypertension is a progressive disease of the pulmonary arteries that begins with increased pulmonary artery pressure, driven by progressive remodeling of the small pulmonary arteries, and ultimately leads to right heart failure and death. Vascular remodeling is the main pathological feature of pulmonary hypertension, but treatments for pulmonary hypertension are lacking. Determining the process of vascular proliferation and dysfunction may be a way to decipher the pathogenesis of pulmonary hypertension. In this review, we summarize the important pathways of pulmonary hypertension pathogenesis. We show how these processes are integrated and emphasize the benign role of aerobic exercise, which, as an adjunctive therapy, may be able to modify vascular remodeling in pulmonary hypertension.

The role and mechanism of AMPK in pulmonary hypertension

Pulmonary hypertension (PH) is a chronic progressive disease with high mortality. There has been more and more research focusing on the role of AMPK in PH. AMPK consists of three subunits-α, β, and γ. The crosstalk among these subunits ultimately leads to a delicate balance to affect PH, which results in conflicting conclusions about the role of AMPK in PH. It is still unclear how these subunits interfere with each other and achieve balance to improve or deteriorate PH. Several signaling pathways are related to AMPK in the treatment of PH, including AMPK/eNOS/NO pathway, Nox4/mTORC2/AMPK pathway, AMPK/BMP/Smad pathway, and SIRT3-AMPK pathway. Among these pathways, the role and mechanism of AMPK/eNOS/NO and Nox4/mTORC2/AMPK pathways are clearer than others, while the SIRT3-AMPK pathway remains still unclear in the treatment of PH. There are drugs targeting AMPK to improve PH, such as metformin (MET), MET combination, and rhodiola extract. In addition, several novel factors target AMPK for improving PH, such as ADAMTS8, TUFM, and Salt-inducible kinases. However, more researches are needed to explore the specific AMPK signaling pathways involved in these novel factors in the future. In conclusion, AMPK plays an important role in PH.

Sodium butyrate improves mitochondrial function and kidney tissue injury in diabetic kidney disease via the AMPK/PGC-1α pathway

PURPOSE

Investigate the mechanism of how sodium butyrate (NaBut) improves mitochondrial function and kidney tissue injury in diabetic kidney disease (DKD) via the AMPK/PGC-1α pathway.

METHODS

Assess the effects of NaBut on glucose and insulin tolerance, urine, and gut microbial composition in db/db and db/m mice. Use flow cytometry and western blotting to detect the effects of NaBut on apoptosis, kidney mitochondrial function, and AMPK/PGC-1α signaling. Use HK-2 cells induced by high glucose (HG) to establish the DKD model in vitro and detect changes in the AMPK/PGC-1α signaling pathway and mitochondrial function after NaBut intervention.

RESULTS

NaBut attenuated blood glucose levels and reversed increases in urine and serum levels of glucose, BUN, Ucr, TG, TC, and UAE in db/db mice. NaBut improved insulin tolerance, reversed PGC-1α and p-AMPK expression level in the kidneys of db/db mice, and improved lipid accumulation and mitochondrial function. NaBut was able to reverse the effects of elevated glucose, compound C, and siRNA-PGC on ROS and ATP levels. Additionally, it increased protein expression of PGC-1α and p-AMPK.

CONCLUSION

NaBut activates the kidney mitochondrial AMPK/PGC-1α signaling pathway and improves mitochondrial dysfunction in DKD, thus protecting kidney tissue in vitro and in vivo.

PGC-1α-mediated angiogenesis prevents pulmonary hypertension in mice

Pulmonary hypertension (PH) is a life-threatening disease characterized by a progressive narrowing of pulmonary arterioles. Although VEGF is highly expressed in lung of patients with PH and in animal PH models, the involvement of angiogenesis remains elusive. To clarify the pathophysiological function of angiogenesis in PH, we compared the angiogenic response in hypoxia (Hx) and SU5416 (a VEGFR2 inhibitor) plus Hx (SuHx) mouse PH models using 3D imaging. The 3D imaging analysis revealed an angiogenic response in the lung of the Hx-PH, but not of the severer SuHx-PH model. Selective VEGFR2 inhibition with cabozantinib plus Hx in mice also suppressed angiogenic response and exacerbated Hx-PH to the same extent as SuHx. Expression of endothelial proliferator-activated receptor γ coactivator 1α (PGC-1α) increased along with angiogenesis in lung of Hx-PH but not SuHx mice. In pulmonary endothelial cell-specific Ppargc1a-KO mice, the Hx-induced angiogenesis was suppressed, and PH was exacerbated along with increased oxidative stress, cellular senescence, and DNA damage. By contrast, treatment with baicalin, a flavonoid enhancing PGC-1α activity in endothelial cells, ameliorated Hx-PH with increased Vegfa expression and angiogenesis. Pulmonary endothelial PGC-1α-mediated angiogenesis is essential for adaptive responses to Hx and might represent a potential therapeutic target for PH.

Mitochondria in hypoxic pulmonary hypertension, roles and the potential targets

Mitochondria are the centrol hub for cellular energy metabolisms. They regulate fuel metabolism by oxygen levels, participate in physiological signaling pathways, and act as oxygen sensors. Once oxygen deprived, the fuel utilizations can be switched from mitochondrial oxidative phosphorylation to glycolysis for ATP production. Notably, mitochondria can also adapt to hypoxia by making various functional and phenotypes changes to meet the demanding of oxygen levels. Hypoxic pulmonary hypertension is a life-threatening disease, but its exact pathgenesis mechanism is still unclear and there is no effective treatment available until now. Ample of evidence indicated that mitochondria play key factor in the development of hypoxic pulmonary hypertension. By hypoxia-inducible factors, multiple cells sense and transmit hypoxia signals, which then control the expression of various metabolic genes. This activation of hypoxia-inducible factors considered associations with crosstalk between hypoxia and altered mitochondrial metabolism, which plays an important role in the development of hypoxic pulmonary hypertension. Here, we review the molecular mechanisms of how hypoxia affects mitochondrial function, including mitochondrial biosynthesis, reactive oxygen homeostasis, and mitochondrial dynamics, to explore the potential of improving mitochondrial function as a strategy for treating hypoxic pulmonary hypertension.

Targeting Mitochondrial Metabolic Dysfunction in Pulmonary Hypertension: Toward New Therapeutic Approaches?

Pulmonary arterial hypertension (PAH) is a rare disease characterized by pulmonary vascular remodeling leading to right heart failure and death. To date, despite the three therapeutic approaches targeting the three major endothelial dysfunction pathways based on the prostacyclin, nitric oxide/cyclic guanosine monophosphate, and endothelin pathways, PAH remains a serious disease. As such, new targets and therapeutic agents are needed. Mitochondrial metabolic dysfunction is one of the mechanisms involved in PAH pathogenesis in part through the induction of a Warburg metabolic state of enhanced glycolysis but also through the upregulation of glutaminolysis, tricarboxylic cycle and electron transport chain dysfunction, dysregulation of fatty acid oxidation or mitochondrial dynamics alterations. The aim of this review is to shed light on the main mitochondrial metabolic pathways involved in PAH and to provide an update on the resulting interesting potential therapeutic perspectives.

Nanoparticle endothelial delivery of PGC-1α attenuates hypoxia-induced pulmonary hypertension by attenuating EndoMT-caused vascular wall remodeling

Pulmonary hypertension (PH) induced by chronic hypoxia is characterized by thickening of pulmonary artery walls, elevated pulmonary vascular resistance, and right-heart failure. Dysfunction of endothelial cells is the hallmark event in the progression of PH. Among various mechanisms, endothelial to mesenchymal transition (EndoMT) has emerged as an important source of endothelial cell dysfunction in PH. However, the mechanisms underlying the EndoMT in PH remain largely unknown. Our results showed that peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) expression was decreased in pulmonary arterial endothelial cells (PAECs) in PH patients and hypoxia-induced PH mouse model compared to the normal controls. Endothelial-specific overexpression of PGC-1α using nanoparticle delivery significantly attenuated the progression of PH, as shown by the significantly decreased right ventricular systolic pressure and diminished artery thickness as well as reduced vascular muscularization. Moreover, Endothelial-specific overexpression of PGC-1α blocked the EndoMT of PAECs during PH, indicating that loss of PGC-1α promotes PH development by mediating EndoMT, which damages the integrity of endothelium. Intriguingly, we found that PGC-1α overexpression rescued the expression of endothelial nitric oxide synthase in mouse lung tissues that was deceased by hypoxia treatment in vivo and in endothelial cells treated with TGF-β in vitro. Consistently, PAECs and vascular smooth muscle co-culture showed that overexpression of PGC-1α in PAECs increases nitric oxide release, which would likely diffuse to smooth muscle cells, where it activates specific protein kinases, and initiates SMC relaxation by diminishing the calcium flux. Endothelial-specific overexpression of PGC-1α also attenuated hypoxia-induced pulmonary artery stiffness which appeared to be caused by both the decreased endothelial nitric oxide production and increased vascular remodeling. Taken together, these results demonstrated that endothelial-specific delivery of PGC-1α prevents PH development by inhibiting EndoMT of PAECs and thus restoring endothelial function and reducing vascular remodeling.

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.

PGC-1 alpha regulates mitochondrial biogenesis to ameliorate hypoxia-inhibited cementoblast mineralization

Hypoxia often occurs in inflammatory tissues, such as tissues affected by periodontitis and apical periodontitis lesions. Mitochondrial biogenesis can be disrupted in hypoxia. Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) is a core factor required for mitochondrial biogenesis. Cementoblasts are root surface lining cells that play an integral role in cementum formation. There is a dearth of research on the effect of hypoxia on cementoblasts and underlying mechanisms, particularly in relation to mitochondrial biogenesis during the hypoxic process. In this study, we found that the expression of hypoxia inducible factor-1α was elevated in apical periodontitis tissues in vivo. In contrast, periapical lesions exhibited a reduction of PGC-1α expression. For in vitro experiments, cobalt chloride (CoCl₂ ) was used to induce hypoxia. We observed that CoCl₂ -induced hypoxia suppressed the mineralization ability and mitochondrial biogenesis of cementoblasts, accompanied by abnormal mitochondria morphology. Furthermore, we found that CoCl₂ blocked the p38 pathway, while it activated the Erk1/2 pathway, with the former upregulating the expression of PGC-1α, while the latter reversed the effects. Overall, our findings demonstrate that mitochondrial biogenesis, especially via PGC-1α, is impaired during cementogenesis in the context of CoCl₂ -induced hypoxia, dependent on the mitogen-activated protein kinase signaling pathway.

Signal Transduction during Metabolic and Inflammatory Reprogramming in Pulmonary Vascular Remodeling

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by (mal)adaptive remodeling of the pulmonary vasculature, which is associated with inflammation, fibrosis, thrombosis, and neovascularization. Vascular remodeling in PAH is associated with cellular metabolic and inflammatory reprogramming that induce profound endothelial and smooth muscle cell phenotypic changes. Multiple signaling pathways and regulatory loops act on metabolic and inflammatory mediators which influence cellular behavior and trigger pulmonary vascular remodeling in vivo. This review discusses the role of bioenergetic and inflammatory impairments in PAH development.

Endothelial Dec1-PPARγ Axis Impairs Proliferation and Apoptosis Homeostasis Under Hypoxia in Pulmonary Arterial Hypertension

Background: The hypoxia-induced pro-proliferative and anti-apoptotic characteristics of pulmonary arterial endothelial cells (PAECs) play critical roles in pulmonary vascular remodeling and contribute to hypoxic pulmonary arterial hypertension (PAH) pathogenesis. However, the mechanism underlying this hypoxic disease has not been fully elucidated.

Methods: Bioinformatics was adopted to screen out the key hypoxia-related genes in PAH. Gain- and loss-function assays were then performed to test the identified hypoxic pathways in vitro. Human PAECs were cultured under hypoxic (3% O₂) or normoxic (21% O₂) conditions. Hypoxia-induced changes in apoptosis and proliferation were determined by flow cytometry and Ki-67 immunofluorescence staining, respectively. Survival of the hypoxic cells was estimated by cell counting kit-8 assay. Expression alterations of the target hypoxia-related genes, cell cycle regulators, and apoptosis factors were investigated by Western blot.

Results: According to the Gene Expression Omnibus dataset (GSE84538), differentiated embryo chondrocyte expressed gene 1-peroxisome proliferative-activated receptor-γ (Dec1-PPARγ) axis was defined as a key hypoxia-related signaling in PAH. A negative correlation was observed between Dec1 and PPARγ expression in patients with hypoxic PAH. In vitro observations revealed an increased proliferation and a decreased apoptosis in PAECs under hypoxia. Furthermore, hypoxic PAECs exhibited remarkable upregulation of Dec1 and downregulation of PPARγ. Dec1 was confirmed to be crucial for the imbalance of proliferation and apoptosis in hypoxic PAECs. Furthermore, the pro-surviving effect of hypoxic Dec1 was mediated through PPARγ inhibition.

Conclusion: For the first time, Dec1-PPARγ axis was identified as a key determinant hypoxia-modifying signaling that is necessary for the imbalance between proliferation and apoptosis of PAECs. These novel endothelial signal transduction events may offer new diagnostic and therapeutic options for patients with hypoxic PAH.

Endothelial cells in the pathogenesis of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a devastating disease that involves pulmonary vasoconstriction, small vessel obliteration, large vessel thickening and obstruction, and development of plexiform lesions. PAH vasculopathy leads to progressive increases in pulmonary vascular resistance, right heart failure and, ultimately, premature death. Besides other cell types that are known to be involved in PAH pathogenesis (e.g. smooth muscle cells, fibroblasts and leukocytes), recent studies have demonstrated that endothelial cells (ECs) have a crucial role in the initiation and progression of PAH. The EC-specific role in PAH is multi-faceted and affects numerous pathophysiological processes, including vasoconstriction, inflammation, coagulation, metabolism and oxidative/nitrative stress, as well as cell viability, growth and differentiation. In this review, we describe how EC dysfunction and cell signalling regulate the pathogenesis of PAH. We also highlight areas of research that warrant attention in future studies, and discuss potential molecular signalling pathways in ECs that could be targeted therapeutically in the prevention and treatment of PAH.

Oxygen sensing, mitochondrial biology and experimental therapeutics for pulmonary hypertension and cancer

The homeostatic oxygen sensing system (HOSS) optimizes systemic oxygen delivery. Specialized tissues utilize a conserved mitochondrial sensor, often involving NDUFS2 in complex I of the mitochondrial electron transport chain, as a site of pO₂-responsive production of reactive oxygen species (ROS). These ROS are converted to a diffusible signaling molecule, hydrogen peroxide (H₂O₂), by superoxide dismutase (SOD2). H₂O₂ exits the mitochondria and regulates ion channels and enzymes, altering plasma membrane potential, intracellular Ca²⁺ and Ca²⁺-sensitization and controlling acute, adaptive, responses to hypoxia that involve changes in ventilation, vascular tone and neurotransmitter release. Subversion of this O₂-sensing pathway creates a pseudohypoxic state that promotes disease progression in pulmonary arterial hypertension (PAH) and cancer. Pseudohypoxia is a state in which biochemical changes, normally associated with hypoxia, occur despite normal pO₂. Epigenetic silencing of SOD2 by DNA methylation alters H₂O₂ production, activating hypoxia-inducible factor 1α, thereby disrupting mitochondrial metabolism and dynamics, accelerating cell proliferation and inhibiting apoptosis. Other epigenetic mechanisms, including dysregulation of microRNAs (miR), increase pyruvate dehydrogenase kinase and pyruvate kinase muscle isoform 2 expression in both diseases, favoring uncoupled aerobic glycolysis. This Warburg metabolic shift also accelerates cell proliferation and impairs apoptosis. Disordered mitochondrial dynamics, usually increased mitotic fission and impaired fusion, promotes disease progression in PAH and cancer. Epigenetic upregulation of dynamin-related protein 1 (Drp1) and its binding partners, MiD49 and MiD51, contributes to the pathogenesis of PAH and cancer. Finally, dysregulation of intramitochondrial Ca²⁺, resulting from impaired mitochondrial calcium uniporter complex (MCUC) function, links abnormal mitochondrial metabolism and dynamics. MiR-mediated decreases in MCUC function reduce intramitochondrial Ca²⁺, promoting Warburg metabolism, whilst increasing cytosolic Ca²⁺, promoting fission. Epigenetically disordered mitochondrial O₂-sensing, metabolism, dynamics, and Ca²⁺ homeostasis offer new therapeutic targets for PAH and cancer. Promoting glucose oxidation, restoring the fission/fusion balance, and restoring mitochondrial calcium regulation are promising experimental therapeutic strategies.

Zafirlukast promotes mitochondrial respiration by stimulating mitochondrial biogenesis in human bronchial epithelial cells

Lung diseases, including asthma, pose a serious global health issue. Loss of mitochondrial function and decreased mitochondrial biogenesis play pivotal roles in the initiation and progression of chronic lung diseases. Thus, maintaining mitochondrial function and homeostasis is an important treatment goal. Zafirlukast is a CysLTR1 antagonist that is widely used as an adjuvant treatment for asthma. In the present study, we investigated the effects of zafirlukast in vitro using human bronchial epithelial cells (BECs). We performed measurements of oxygen consumption and bioenergetics and found that zafirlukast increased mitochondrial respiration and biogenesis in human BECs as evidenced by increased mitochondrial mass and mtDNA/nDNA. Through real-time PCR and western blot analysis, we found that zafirlukast significantly increased the expression of PGC-1α, NRF1, and TFAM at both the mRNA and protein levels. Finally, we determined that these effects are mediated through CREB signaling and that inhibition of CREB with its specific inhibitor H89 abolished the effects of zafirlukast described above. Thus, zafirlukast might have potential in enhancing mitochondrial function by promoting mitochondrial biogenesis in human bronchial epithelial cells through upregulating the expression of PGC-1α and activating the CREB pathway.

Endothelial cell crosstalk improves browning but hinders white adipocyte maturation in 3D engineered adipose tissue

Central to the development of adipose tissue (AT) engineered models is the supporting vasculature. It is a key part of AT function and long-term maintenance, but the crosstalk between adipocytes and endothelial cells is not well understood. Here, we directly co-culture the two cell types at varying ratios in a 3D Type I collagen gel. Constructs were evaluated for adipocyte maturation and function and vascular network organization. Further, these constructs were treated with forskolin, a beta-adrenergic agonist, to stimulate lipolysis and browning. Adipocytes in co-cultures were found to be less mature than an adipocyte-only control, shown by smaller lipid droplets and downregulation of key adipocyte-related genes. The most extensive vascular network formation was found in the 1:1 co-culture, supported by vascular endothelial growth factor (VEGF) upregulation. After forskolin treatment, the presence of endothelial cells was shown to upregulate PPAR coactivator 1 alpha (PGC-1α) and leptin, but not uncoupling protein 1 (UCP1), suggesting a specific crosstalk that enhances early stages of browning.

The effect of extracellular vesicles on the regulation of mitochondria under hypoxia

Mitochondria are indispensable organelles for maintaining cell energy metabolism, and also are necessary to retain cell biological function by transmitting information as signal organelles. Hypoxia, one of the important cellular stresses, can directly regulates mitochondrial metabolites and mitochondrial reactive oxygen species (mROS), which affects the nuclear gene expression through mitochondrial retrograde signal pathways, and also promotes the delivery of signal components into cytoplasm, causing cellular injury. In addition, mitochondria can also trigger adaptive mechanisms to maintain mitochondrial function in response to hypoxia. Extracellular vesicles (EVs), as a medium of information transmission between cells, can change the biological effects of receptor cells by the release of cargo, including nucleic acids, proteins, lipids, mitochondria, and their compositions. The secretion of EVs increases in cells under hypoxia, which indirectly changes the mitochondrial function through the uptake of contents by the receptor cells. In this review, we focus on the mitochondrial regulation indirectly through EVs under hypoxia, and the possible mechanisms that EVs cause the changes in mitochondrial function. Finally, we discuss the significance of this EV-mitochondria axis in hypoxic diseases.

The possible role of sirtuin 5 in the pathogenesis of apical periodontitis

OBJECTIVES

We investigated the relation between expression of sirtuin 5 (SIRT5) in osteoblastic cells and progression of apical periodontitis. The role of SIRT5 in hypoxia-induced reactive oxygen species (ROS) formation and osteoblast apoptosis was also examined.

MATERIALS AND METHODS

Progression of rat apical periodontitis was monitored by conventional radiography and microcomputed tomography. SIRT5 and oxidative stress biomarker 8-OHdG in bone-lining cells were assessed by immunohistochemistry. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling was used to demonstrate apoptosis. In primary human osteoblasts cultured under hypoxia, Western blot was used to analyze SIRT5 expression and cleavage of pro-caspase 3 and poly(ADP-ribose) polymerase (PARP). SIRT5 was overexpressed through lentiviral technique. ROS formation and mitochondrial membrane potential changes were assessed by MitoSOX-Red and JC-1 fluorescence, respectively. Immunofluorescence microscope was used to evaluate mitochondrial release of cytochrome c.

RESULTS

In rat apical periodontitis, disease progression was accompanied by decreased expression of SIRT5, increased oxidative stress, and enhanced apoptosis in bone-lining cells. SIRT5 was suppressed in cultured osteoblasts under hypoxia. SIRT5 overexpression ameliorated hypoxia-enhanced ROS formation, mitochondrial depolarization, cytochrome c leakage, activation of caspase-3, and PARP fragmentation.

CONCLUSIONS

SIRT5 is able to alleviate hypoxia-enhanced osteoblast apoptosis. SIRT5 augmentation may have therapeutic potential for apical periodontitis.

Perivascular Inflammation in Pulmonary Arterial Hypertension

Perivascular inflammation is a prominent pathologic feature in most animal models of pulmonary hypertension (PH) as well as in pulmonary arterial hypertension (PAH) patients. Accumulating evidence suggests a functional role of perivascular inflammation in the initiation and/or progression of PAH and pulmonary vascular remodeling. High levels of cytokines, chemokines, and inflammatory mediators can be detected in PAH patients and correlate with clinical outcome. Similarly, multiple immune cells, including neutrophils, macrophages, dendritic cells, mast cells, T lymphocytes, and B lymphocytes characteristically accumulate around pulmonary vessels in PAH. Concomitantly, vascular and parenchymal cells including endothelial cells, smooth muscle cells, and fibroblasts change their phenotype, resulting in altered sensitivity to inflammatory triggers and their enhanced capacity to stage inflammatory responses themselves, as well as the active secretion of cytokines and chemokines. The growing recognition of the interaction between inflammatory cells, vascular cells, and inflammatory mediators may provide important clues for the development of novel, safe, and effective immunotargeted therapies in PAH.

Molecular mechanisms of right ventricular dysfunction in pulmonary arterial hypertension: focus on the coronary vasculature, sex hormones, and glucose/lipid metabolism

Pulmonary arterial hypertension (PAH) is a rare, life-threatening condition characterized by dysregulated metabolism, pulmonary vascular remodeling, and loss of pulmonary vascular cross-sectional area due to a variety of etiologies. Right ventricular (RV) dysfunction in PAH is a critical mediator of both long-term morbidity and mortality. While combinatory oral pharmacotherapy and/or intravenous prostacyclin aimed at decreasing pulmonary vascular resistance (PVR) have improved clinical outcomes, there are currently no treatments that directly address RV failure in PAH. This is, in part, due to the incomplete understanding of the pathogenesis of RV dysfunction in PAH. The purpose of this review is to discuss the current understanding of key molecular mechanisms that cause, contribute and/or sustain RV dysfunction, with a special focus on pathways that either have led to or have the potential to lead to clinical therapeutic intervention. Specifically, this review discusses the mechanisms by which vessel loss and dysfunctional angiogenesis, sex hormones, and metabolic derangements in PAH directly contribute to RV dysfunction. Finally, this review discusses limitations and future areas of investigation that may lead to novel understanding and therapeutic interventions for RV dysfunction in PAH.

Mitochondria in the Pulmonary Vasculature in Health and Disease: Oxygen-Sensing, Metabolism, and Dynamics

In lung vascular cells, mitochondria serve a canonical metabolic role, governing energy homeostasis. In addition, mitochondria exist in dynamic networks, which serve noncanonical functions, including regulation of redox signaling, cell cycle, apoptosis, and mitochondrial quality control. Mitochondria in pulmonary artery smooth muscle cells (PASMC) are oxygen sensors and initiate hypoxic pulmonary vasoconstriction. Acquired dysfunction of mitochondrial metabolism and dynamics contribute to a cancer-like phenotype in pulmonary arterial hypertension (PAH). Acquired mitochondrial abnormalities, such as increased pyruvate dehydrogenase kinase (PDK) and pyruvate kinase muscle isoform 2 (PKM2) expression, which increase uncoupled glycolysis (the Warburg phenomenon), are implicated in PAH. Warburg metabolism sustains energy homeostasis by the inhibition of oxidative metabolism that reduces mitochondrial apoptosis, allowing unchecked cell accumulation. Warburg metabolism is initiated by the induction of a pseudohypoxic state, in which DNA methyltransferase (DNMT)-mediated changes in redox signaling cause normoxic activation of HIF-1α and increase PDK expression. Furthermore, mitochondrial division is coordinated with nuclear division through a process called mitotic fission. Increased mitotic fission in PAH, driven by increased fission and reduced fusion favors rapid cell cycle progression and apoptosis resistance. Downregulation of the mitochondrial calcium uniporter complex (MCUC) occurs in PAH and is one potential unifying mechanism linking Warburg metabolism and mitochondrial fission. Mitochondrial metabolic and dynamic disorders combine to promote the hyperproliferative, apoptosis-resistant, phenotype in PAH PASMC, endothelial cells, and fibroblasts. Understanding the molecular mechanism regulating mitochondrial metabolism and dynamics has permitted identification of new biomarkers, nuclear and CT imaging modalities, and new therapeutic targets for PAH. © 2020 American Physiological Society. Compr Physiol 10:713-765, 2020.

Redox Biology of Peroxisome Proliferator-Activated Receptor-γ in Pulmonary Hypertension

Significance: Peroxisome proliferator-activated receptor-gamma (PPARγ) maintains pulmonary vascular health through coordination of antioxidant defense systems, inflammation, and cellular metabolism. Insufficient PPARγ contributes to pulmonary hypertension (PH) pathogenesis, whereas therapeutic restoration of PPARγ activity attenuates PH in preclinical models. Recent Advances: Numerous studies in the past decade have elucidated the complex mechanisms by which PPARγ in the pulmonary vasculature and right ventricle (RV) protects against PH. The scope of PPARγ-interconnected pathways continues to expand and includes induction of antioxidant genes, transrepression of inflammatory signaling, regulation of mitochondrial biogenesis and bioenergetic integrity, control of cell cycle and proliferation, and regulation of vascular tone through interactions with nitric oxide and endogenous vasoactive molecules. Furthermore, PPARγ interacts with an extensive regulatory network of transcription factors and microRNAs leading to broad impact on cell signaling. Critical Issues: Abundant evidence suggests that targeting PPARγ exerts diverse salutary effects in PH and represents a novel and potentially translatable therapeutic strategy. However, progress has been slowed by an incomplete understanding of how specific PPARγ pathways are critically disrupted across PH disease subtypes and lack of optimal pharmacological ligands. Future Directions: Recent studies indicate that ligand-induced post-translational modifications of the PPARγ receptor differentially induce therapeutic benefits versus adverse side effects of PPARγ receptor activation. Strategies to selectively target PPARγ activity in diseased cells of pulmonary circulation and RV, coupled with development of ligands designed to specifically regulate post-translational PPARγ modifications, may unlock the full therapeutic potential of this versatile master transcriptional and metabolic regulator in PH.

Mitochondrial Dysfunction: Metabolic Drivers of Pulmonary Hypertension

Significance: Pulmonary hypertension (PH) is a progressive disease characterized by pulmonary vascular remodeling and lung vasculopathy. The disease displays progressive dyspnea, pulmonary artery uncoupling and right ventricular (RV) dysfunction. The overall survival rate is ranging from 28-72%. Recent Advances: The molecular events that promote the development of PH are complex and incompletely understood. Metabolic impairment has been proposed to contribute to the pathophysiology of PH with evidence for mitochondrial dysfunction involving the electron transport chain proteins, antioxidant enzymes, apoptosis regulators, and mitochondrial quality control. Critical Issues: It is vital to characterize the mechanisms by which mitochondrial dysfunction contribute to PH pathogenesis. This review focuses on the currently available publications that supports mitochondrial mechanisms in PH pathophysiology. Future Directions: Further studies of these metabolic mitochondrial alterations in PH could be viable targets of diagnostic and therapeutic intervention.

Paeonol protects mitochondrial injury and prevents pulmonary vascular remodeling in hypoxia

Mitochondrial injury of pulmonary artery smooth muscle cells (PASMCs) is an important stage in the development of pulmonary arterial hypertension (PAH). Recent studies revealed that Paeonol exerts anti-proliferative effects on vascular smooth muscle cells. However, whether Paeonol is directly involved in mitochondrial injury related to PAH remains unknown. Here, we found that hypoxia-induced mitochondrial injury in vivo was alleviated in the presence of Paeonol. Hypoxia mediated the mitochondrial injuries in PASMCs in vitro, including decreased ATP generation, morphological alterations, mitochondrial polarization and increased reactive oxygen species production, which were suppressed by Paeonol. Our results also indicated that the expression of peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC-1α) was regulated by Paeonol. Paeonol caused significant alterations in mitochondrion-dependent apoptosis through PGC-1α in PASMCs. Taken together, these results provide the first evidence confirming the protective effect of Paeonol in mediating mitochondrial injury under hypoxia and elucidating the necessary role of PGC-1α in the effects of Paeonol in inducing PASMC apoptosis.

Targeting mitochondria-associated membranes as a potential therapy against endothelial injury induced by hypoxia

Mitochondrial dysfunction plays a principal role in hypoxia-induced endothelial injury, which is involved in hypoxic pulmonary hypertension and ischemic cardiovascular diseases. Recent studies have identified mitochondria-associated membranes (MAMs) that modulate mitochondrial function under a variety of pathophysiological conditions such as high-fat diet-mediated insulin resistance, hypoxia reoxygenation-induced myocardial death, and hypoxia-evoked vascular smooth muscle cell proliferation. However, the role of MAMs in hypoxia-induced endothelial injury remains unclear. To explore this further, human umbilical vein endothelial cells and human pulmonary artery endothelial cells were exposed to hypoxia (1% O₂ ) for 24 hours. An increase in MAM formation was uncovered by immunoblotting and immunofluorescence. Then, we performed small interfering RNA transfection targeted to MAM constitutive proteins and explored the biological effects. Knockdown of MAM constitutive proteins attenuated hypoxia-induced elevation of mitochondrial Ca²⁺ and repressed mitochondrial impairment, leading to an increase in mitochondrial membrane potential and ATP production and a decline in reactive oxygen species. Then, we found that MAM disruption mitigated cell apoptosis and promoted cell survival. Next, other protective effects, such as those pertaining to the repression of inflammatory response and the promotion of NO synthesis, were investigated. With the disruption of MAMs under hypoxia, inflammatory molecule expression was repressed, and the eNOS-NO pathway was enhanced. This study demonstrates that the disruption of MAMs might be of therapeutic value for treating endothelial injury under hypoxia, suggesting a novel strategy for preventing hypoxic pulmonary hypertension and ischemic injuries.

Aralia taibaiensis Protects against I/R-Induced Brain Cell Injury through the Akt/SIRT1/FOXO3a Pathway

BACKGROUND

Saponin from Aralia taibaiensis (sAT) showed excellent antioxidative effects in several models; however, its effects on brain cells were unknown to us. The present study was designed to evaluate the protective effects of sAT on ischemia/reperfusion- (I/R-) induced injury and clarify its mechanisms.

METHODS

In vitro, HT22 cells were pretreated with sAT and then subjected to I/R. Apoptosis rate, mitochondrial function, and antioxidant proteins were measured. To clarify the mechanisms, siRNA were used. In vivo, sAT was pretreated through intragastric administration for 7 days and the I/R model was induced. The neurobehavioral scores, infarction volumes, and some cytokines in the brain were measured. Protein levels were investigated by Western blotting.

RESULTS

The results showed that sAT treatment significantly protected cells from I/R-induced cell apoptosis and mitochondrial dysfunction. The antioxidant protein levels were increased in a dose-dependent manner. Further study revealed that sAT induced the deacetylation and phosphorylation of PGC-1α and FOXO3a. sAT treatment also induced the phosphorylation levels of Akt and the expression levels of SIRT1. Using the specific targeted siRNA transfection, the interplay relationship between Akt, SIRT1, PGC-1α, and FOXO3a was verified. Furthermore, the same protective effects were also observed in rats subjected to I/R.

CONCLUSION

sAT protected brain cells from I/R-induced mitochondrial oxidative stress and dysfunction through regulating the Akt/SIRT1/FOXO3a/PGC-1α pathway.

Mutual promotion of FGF21 and PPARγ attenuates hypoxia-induced pulmonary hypertension

IMPACT STATEMENT

In this study, we reported for the first time that FGF21 alleviated hypoxia-induced pulmonary hypertension through attenuation of increased pulmonary arterial pressure, pulmonary arterial remodeling and collagen deposition in vivo, and we confirmed the mutual promotion of FGF21 and PPARγ in hypoxia-induced pulmonary hypertension. Additionally, we found that FGF21 and PPARγ mutually promote each other's expression via the AMPK/PGC-1α pathway and KLB protein in vitro and in vivo. Pulmonary hypertension is a progressive and serious pathological phenomenon with a poor prognosis, and current therapies are highly limited. Our results provide novel insight into potential clinical therapies for pulmonary hypertension and establish the possibility of using this drug combination and potential dosage reductions in clinical settings.

Review on Chamber-Specific Differences in Right and Left Heart Reactive Oxygen Species Handling

Reactive oxygen species (ROS) exert signaling character (redox signaling), or damaging character (oxidative stress) on cardiac tissue depending on their concentration and/or reactivity. The steady state of ROS concentration is determined by the interplay between its production (mitochondrial, cytosolic, and sarcolemmal enzymes) and ROS defense enzymes (mitochondria, cytosol). Recent studies suggest that ROS regulation is different in the left and right ventricle of the heart, specifically by a different activity of superoxide dismutase (SOD). Mitochondrial ROS defense seems to be lower in right ventricular tissue compared to left ventricular tissue. In this review we summarize the current evidence for heart chamber specific differences in ROS regulation that may play a major role in an observed inability of the right ventricle to compensate for cardiac stress such as pulmonary hypertension. Based on the current knowledge regimes to increase ROS defense in right ventricular tissue should be in the focus for the development of future therapies concerning right heart failure.

Effects of tumor necrosis factor-α-induced exosomes on the endothelial cellular behavior, metabolism and bioenergetics

OBJECTIVE

To investigate the effects of TNF-α-induced exosomes release on the biological behavior, metabolism, and bioenergetics of HUVECs.

METHODS

Exosomes were isolated from conditioned media of HUVECs by ultracentrifugation after treatment with or without TNF-α. HUVECs were treated with or without TNF-α, or different concentrations of exosomes isolated from conditioned media with or without TNF-α induction (T_Exo and C_Exo , respectively).

RESULTS

The results showed that TNF-α significantly inhibited migration, tube formation, and increased apoptosis rate of HUVECs compared with controls. Furthermore, TNF-α-induced exosomes (T_Exo ) rather than C_Exo , indicated similar effects to inhibit migration, tube formation and promote endothelial apoptosis. Although TNF-α treatment did not show a statistical difference, T_Exo significantly inhibited extracellular OCR compared with controls. T_Exo could significantly inhibited intracellular OCR in a hypoxia condition. TNF-α significantly increased L-ECA compared with control cells, and T_Exo showed similar stimulative effect on L-ECA.

CONCLUSIONS

TNF-α-induced exosomes could significantly (a) change migration, tube formation, and apoptosis; (b) inhibit endothelial extracellular OCR and intracellular OCR (hypoxia); (c) increase glycolysis rate of the endothelial cells. These data provide new evidence for exploring endothelial behavior regulation using exosomes and their effects on endothelial metabolism and bioenergetics.

Yiqihuoxue decoction protects against post-myocardial infarction injury via activation of cardiomyocytes PGC-1α expression

BACKGROUND

Mitochondrial dysfunction has been implicated in the pathogenesis of ischemic heart disease, exacerbating cardiomyocytes injury in myocardial infarction (MI). Peroxisome proliferator-activated receptor gamma co-activator (PGC-1α) has been recognized as the key regulator of mitochondrial biogenesis and energy metabolism. Yiqihuoxue decoction (YQHX), a Traditional Chinese Medicine (TCM) prescription, can prevent and treat ischemic heart disease. However, the mechanisms of YQHX on PGC-1α expression in the ischemic heart have remained unclear.

METHODS

Myocardial ischemia rat model and ischemia/hypoxia injury model in the cardiomyocytes were used to minic human cardiovascular disease. Rats were randomly assigned into 4 groups: Sham, Model, YQHX (8.2 g/kg) and Trimetazidine (10 mg/kg) group. 28 days after MI, cardiac functions and morphology were detected by echocardiography and HE staining, respectively. In vitro, the effects of YQHX on H9c2 cell viability, LDH and ROS were detected, respectively. PGC-1α relevant proteins were evaluated by Western blotting.

RESULTS

In vivo, echocardiography and HE staining results showed that YQHX improved cardiac functions and modified pathological changes. YQHX enhanced PGC-1α expression and improved the mitochondrial ultrastructure and functions in rats MI model for 4 weeks. Further, we explored its potential mechanisms in cardiomyocytes. In vitro, YQHX significantly enhanced cell viability and reduced LDH release and ROS production induced by hypoxia in cardiomyocytes. Interestingly, exposure of cardiomyocytes to hypoxic conditions for 12 h induced the downregulation of PGC-1α expression, but the expression levels nearly returned to the normal state after hypoxia for 24 h. YQHX significantly enhanced PGC-1α expression between 12 h and 24 h induced by hypoxia through a mechanism associated with the activation of AMPK phosphorylation in H9c2 cells. In addition, YQHX upregulated the expression of Tfam and NRF-1, while NRF-1 expression was completely blocked by an AMPK inhibitor. YQHX largely restored the mitochondrial morphology and increased mitochondrial membrane potential in hypoxia-induced injury. Furthermore, the UHPLC-LTQ-Orbitrap-MSn analysis found that there were 87 chemical constituents in YQHX.

CONCLUSIONS

These results suggest that the protective effect of YQHX on cardiomyocytes against hypoxia-induced injury may be attributed to activation of PGC-1α and maintenance of mitochondrial functions through a mechanism involving the activation of AMPK phosphorylation.

Mitochondrial metabolism in pulmonary hypertension: beyond mountains there are mountains

Pulmonary hypertension (PH) is a heterogeneous and fatal disease of the lung vasculature, where metabolic and mitochondrial dysfunction may drive pathogenesis. Similar to the Warburg effect in cancer, a shift from mitochondrial oxidation to glycolysis occurs in diseased pulmonary vessels and the right ventricle. However, appreciation of metabolic events in PH beyond the Warburg effect is only just emerging. This Review discusses molecular, translational, and clinical concepts centered on the mitochondria and highlights promising, controversial, and challenging areas of investigation. If we can move beyond the "mountains" of obstacles in this field and elucidate these fundamental tenets of pulmonary vascular metabolism, such work has the potential to usher in much-needed diagnostic and therapeutic approaches for the mitochondrial and metabolic management of PH.

Cytoprotective Effect of the UCP2-SIRT3 Signaling Pathway by Decreasing Mitochondrial Oxidative Stress on Cerebral Ischemia-Reperfusion Injury

Recovered blood supply after cerebral ischemia for a certain period of time fails to restore brain function, with more severe dysfunctional problems developing, called cerebral ischemia–reperfusion injury (CIR). CIR involves several extremely complex pathophysiological processes in which the interactions between key factors at various stages have not been fully elucidated. Mitochondrial dysfunction is one of the most important mechanisms of CIR. The mitochondrial deacetylase, sirtuin 3 (SIRT3), can inhibit mitochondrial oxidative stress by deacetylation, to maintain mitochondrial stability. Uncoupling protein 2 (UCP2) regulates ATP (Adenosine triphosphate) and reactive oxygen species production by affecting the mitochondrial respiratory chain, which may play a protective role in CIR. Finally, we propose that UCP2 regulates the activity of SIRT3 through sensing the energy level and, in turn, maintaining the mitochondrial steady state, which demonstrates a cytoprotective effect on CIR.

Suppression of NADPH oxidase attenuates hypoxia-induced dysfunctions of endothelial progenitor cells

NADPH oxidases (NOX) - derived reactive oxygen species (ROS) contribute to oxidative injury in hypoxia-induced pulmonary arterial hypertension. This study aims to evaluate the status of NOX in endothelial progenitor cells (EPCs) under hypoxic condition and to determine whether NOX inhibitors could attenuate hypoxia-induced dysfunctions of EPCs. EPCs were isolated from peripheral blood of SD rats and subjected to hypoxia (O2/N2/CO2, 1/94/5) for 24 h. The cells were collected for β-galactosidase or Hoechst staining, or for functional analysis (migration, adhesion and tube formation). The NOX expression, activity and H2O2 content in EPCs were measured. The results showed that hypoxia treatment promoted EPC senescence and apoptosis, accompanied by the deteriorated functions of EPCs (the reduced abilities in adhesion, migration and tube formation), as well as an increase in NOX2 and NOX4 expression, NOX activity and H2O2 production, these phenomena were attenuated by NOX inhibitors. Furthermore, administration of catalase could also improve the functions of hypoxia-treated EPCs. Based on these observations, we conclude that NOX-derived ROS contributes to the dysfunctions of EPCs under hypoxic condition. Thus, suppression of NOX may provide a novel strategy to improve endothelial functions in hypoxia-relevant diseases.

Glycyrrhizic Acid Prevents Diabetic Nephropathy by Activating AMPK/SIRT1/PGC-1α Signaling in db/db Mice

Diabetic nephropathy (DN) is a major cause of end-stage renal disease (ESRD). Glycyrrhizic acid (GA) is an effective inhibitor of reactive oxygen species (ROS) production. We investigated the role of GA in the progression of renal injury in DN. Albumin (Alb)/creatinine (crea) levels were significantly lower, and renal histopathology was attenuated in the diabetic db/db mice that were treated with GA (15 mg/kg via intraperitoneal injection) once per day for eight weeks. These changes were associated with significantly lower levels of α-smooth muscle actin (α-SMA) and transforming growth factor β1 (TGF-β1) expression. Additionally, diabetic db/db mice displayed more terminal deoxynucleotidyl transferase-mediated nick-end labeling- (TUNEL-) positive nuclei and diabetes-induced ROS production in the kidneys, and these effects were attenuated by the treatment with GA, which activated adenosine monophosphate-activated protein kinase (AMPK)/silent information regulator 1 (SIRT1)/peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) signaling in the kidneys. In summary, in diabetic db/db mice, the effect of GA on DN involved, in part, the inhibition of ROS and the activation of AMPK/SIRT1/PGC-1α signaling in the kidneys. GA, therefore, shows therapeutic potential for preventing and treating DN.

Emerging concepts in smooth muscle contributions to airway structure and function: implications for health and disease

Airway structure and function are key aspects of normal lung development, growth, and aging, as well as of lung responses to the environment and the pathophysiology of important diseases such as asthma, chronic obstructive pulmonary disease, and fibrosis. In this regard, the contributions of airway smooth muscle (ASM) are both functional, in the context of airway contractility and relaxation, as well as synthetic, involving production and modulation of extracellular components, modulation of the local immune environment, cellular contribution to airway structure, and, finally, interactions with other airway cell types such as epithelium, fibroblasts, and nerves. These ASM contributions are now found to be critical in airway hyperresponsiveness and remodeling that occur in lung diseases. This review emphasizes established and recent discoveries that underline the central role of ASM and sets the stage for future research toward understanding how ASM plays a central role by being both upstream and downstream in the many interactive processes that determine airway structure and function in health and disease.