Mitochondrial transplantation attenuates hypoxic pulmonary hypertension

Considerations for developing mitochondrial transplantation techniques for individualized medicine

Tweetable abstract Mitochondrial transplantation has been used to treat various diseases associated with mitochondrial dysfunction. Here, we highlight the considerations in quality control mechanisms that should be considered in the context of mitochondrial transplantation.

Angiogenic activity of mitochondria; beyond the sole bioenergetic organelle

Angiogenesis is a complex process that involves the expansion of the pre-existing vascular plexus to enhance oxygen and nutrient delivery and is stimulated by various factors, including hypoxia. Since the process of angiogenesis requires a lot of energy, mitochondria play an important role in regulating and promoting this phenomenon. Besides their roles as an oxidative metabolism base, mitochondria are potential bioenergetics organelles to maintain cellular homeostasis via sensing alteration in oxygen levels. Under hypoxic conditions, mitochondria can regulate angiogenesis through different factors. It has been indicated that unidirectional and bidirectional exchange of mitochondria or their related byproducts between the cells is orchestrated via different intercellular mechanisms such as tunneling nanotubes, extracellular vesicles, and gap junctions to maintain the cell homeostasis. Even though, the transfer of mitochondria is one possible mechanism by which cells can promote and regulate the process of angiogenesis under reperfusion/ischemia injury. Despite the existence of a close relationship between mitochondrial donation and angiogenic response in different cell types, the precise molecular mechanisms associated with this phenomenon remain unclear. Here, we aimed to highlight the possible role of mitochondria concerning angiogenesis, especially the role of mitochondrial transport and the possible relation of this transfer with autophagy, the housekeeping phenomenon of cells, and angiogenesis.

Mitochondrial transplantation: the advance to therapeutic application and molecular modulation

Mitochondrial transplantation provides a novel methodology for rescue of cell viability and cell function following ischemia-reperfusion injury and applications for other pathologies are expanding. In this review we present our methods and acquired data and evidence accumulated to support the use of mitochondrial transplantation.

p53 contributes to cardiovascular diseases via mitochondria dysfunction: A new paradigm

Cardiovascular diseases (CVDs) are leading causes of global mortality; however, their underlying mechanisms remain unclear. The tumor suppressor factor p53 has been extensively studied for its role in cancer and is also known to play an important role in regulating CVDs. Abnormal p53 expression levels and modifications contribute to the occurrence and development of CVDs. Additionally, mounting evidence underscores the critical involvement of mitochondrial dysfunction in CVDs. Notably, studies indicate that p53 abnormalities directly correlate with mitochondrial dysfunction and may even interact with each other. Encouragingly, small molecule inhibitors targeting p53 have exhibited remarkable effects in animal models of CVDs. Moreover, therapeutic strategies aimed at mitochondrial-related molecules and mitochondrial replacement therapy have demonstrated their advantageous potential. Therefore, targeting p53 or mitochondria holds immense promise as a pioneering therapeutic approach for combating CVDs. In this comprehensive review, we delve into the mechanisms how p53 influences mitochondrial dysfunction, including energy metabolism, mitochondrial oxidative stress, mitochondria-induced apoptosis, mitochondrial autophagy, and mitochondrial dynamics, in various CVDs. Furthermore, we summarize and discuss the potential significance of targeting p53 or mitochondria in the treatment of CVDs.

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.

Mitochondrial transplantation as a novel therapeutic strategy for cardiovascular diseases

Cardiovascular disease (CVD) is the leading cause of noncommunicable disease-related death worldwide, and effective therapeutic strategies against CVD are urgently needed. Mitochondria dysfunction involves in the onset and development of CVD. Nowadays, mitochondrial transplantation, an alternative treatment aimed at increasing mitochondrial number and improving mitochondrial function, has been emerged with great therapeutic potential. Substantial evidence indicates that mitochondrial transplantation improves cardiac function and outcomes in patients with CVD. Therefore, mitochondrial transplantation has profound implications in the prevention and treatment of CVD. Here, we review the mitochondrial abnormalities that occur in CVD and summarize the therapeutic strategies of mitochondrial transplantation for CVD.

Emerging roles of mitochondria in animal regeneration

The regeneration capacity after an injury is critical to the survival of living organisms. In animals, regeneration ability can be classified into five primary types: cellular, tissue, organ, structure, and whole-body regeneration. Multiple organelles and signaling pathways are involved in the processes of initiation, progression, and completion of regeneration. Mitochondria, as intracellular signaling platforms of pleiotropic functions in animals, have recently gained attention in animal regeneration. However, most studies to date have focused on cellular and tissue regeneration. A mechanistic understanding of the mitochondrial role in large-scale regeneration is unclear. Here, we reviewed findings related to mitochondrial involvement in animal regeneration. We outlined the evidence of mitochondrial dynamics across different animal models. Moreover, we emphasized the impact of defects and perturbation in mitochondria resulting in regeneration failure. Ultimately, we discussed the regulation of aging by mitochondria in animal regeneration and recommended this for future study. We hope this review will serve as a means to advocate for more mechanistic studies of mitochondria related to animal regeneration on different scales.

Rescuers from the Other Shore: Intercellular Mitochondrial Transfer and Its Implications in Central Nervous System Injury and Diseases

As the powerhouse and core of cellular metabolism and survival, mitochondria are the essential organelle in mammalian cells and maintain cellular homeostasis by changing their content and morphology to meet demands through mitochondrial quality control. It has been observed that mitochondria can move between cells under physiological and pathophysiological conditions, which provides a novel strategy for preserving mitochondrial homeostasis and also a therapeutic target for applications in clinical settings. Therefore, in this review, we will summarize currently known mechanisms of intercellular mitochondrial transfer, including modes, triggers, and functions. Due to the highly demanded energy and indispensable intercellular linkages of the central nervous system (CNS), we highlight the mitochondrial transfer in CNS. We also discuss future application possibilities and difficulties that need to be addressed in the treatment of CNS injury and diseases. This clarification should shed light on its potential clinical applications as a promising therapeutic target in neurological diseases. Intercellular mitochondrial transfer maintains the homeostasis of central nervous system (CNS), and its alteration is related to several neurological diseases. Supplementing exogenous mitochondrial donor cells and mitochondria, or utilizing some medications to regulate the process of transfer might mitigate the disease and injury.

Mitochondrial Transfer Regulates Cell Fate Through Metabolic Remodeling in Osteoporosis

Mitochondria are the powerhouse of eukaryotic cells, which regulate cell metabolism and differentiation. Recently, mitochondrial transfer between cells has been shown to direct recipient cell fate. However, it is unclear whether mitochondria can translocate to stem cells and whether this transfer alters stem cell fate. Here, mesenchymal stem cell (MSC) regulation is examined by macrophages in the bone marrow environment. It is found that macrophages promote osteogenic differentiation of MSCs by delivering mitochondria to MSCs. However, under osteoporotic conditions, macrophages with altered phenotypes, and metabolic statuses release oxidatively damaged mitochondria. Increased mitochondrial transfer of M1-like macrophages to MSCs triggers a reactive oxygen species burst, which leads to metabolic remodeling. It is showed that abnormal metabolism in MSCs is caused by the abnormal succinate accumulation, which is a key factor in abnormal osteogenic differentiation. These results reveal that mitochondrial transfer from macrophages to MSCs allows metabolic crosstalk to regulate bone homeostasis. This mechanism identifies a potential target for the treatment of osteoporosis.

Mitotherapy in doxorubicin induced cardiotoxicity: A promising strategy to reduce the complications of treatment

AIMS

Doxorubicin is a potent and broad-spectrum antineoplastic medication prescribed for both solid and hematological malignancies. Despite its value, the clinical use of doxorubicin is limited due to cardio-oncologic complication and cardiotoxic adverse effect. Among the mechanisms proposed for its toxicity, mitochondrial dysfunction has gained more attention. Therefore, if damaged mitochondria are replaced by normal efficient mitochondria, cardiac toxicity is expected to be reduced or improved. In this way, we have studied the efficiency of transplantation of freshly isolated rat liver mitochondria in neonatal rat cardiomyocytes that have been damaged by doxorubicin.

MATERIALS AND METHODS

For this purpose, isolated mitochondria were characterized using mitochondrial complex II, membrane potential and swelling evaluations, and also fluorescence and electron microscopy. Afterward, the effect of mitotherapy on the damaged cardiomyocytes was investigated by using annexin V/PI staining, MTT, ROS, MMP, lipid peroxidation, GSH and ATP evaluations.

KEY FINDINGS AND SIGNIFICANCE

Transplanted mitochondria could remarkably enter the neonatal rat cardiomyocytes. Addition of mitochondria to the damaged cardiomyocytes, significantly increased cell viability by reducing the level of reactive oxygen species and lipid peroxidation, increasing of ∆Ψ, ATP and GSH contents and decreasing of apoptotic and necrotic cell death. Our results showed that mitotherapy has a significant restorative effect on cardiotoxicity induced by doxorubicin, which promises a better future to reduce the complications of cancer treatment.

Targeted Mitochondrial Delivery to Hepatocytes: A Review

Defects in mitochondria are responsible for various genetic and acquired diseases. Mitochondrial transplantation, a method that involves introduction of healthy donor mitochondria into cells with dysfunctional mitochondria, could offer a novel approach to treat such diseases. Some studies have demonstrated the therapeutic benefit of mitochondrial transplantation and targeted delivery in vivo and in vitro within hepatocytes and the liver. This review discusses the issues regarding isolation and delivery of mitochondria to hepatocytes and the liver, and examines the existing literature in order to elucidate the utility and practicality of mitochondrial transplantation in the treatment of liver disease. Studies reviewed demonstrate that mitochondrial uptake could specifically target hepatocytes, address the challenge of non-specific localization of donor mitochondria, and provide evidence of changes in liver function following injection of mitochondria into mouse and rat disease models. While potential benefits and advantages of mitochondrial transplantation are evident, more research is needed to determine the practicality of mitochondrial transplantation for the treatment of genetic and acquired liver diseases.

Reviewing the suitability of mitochondrial transplantation as therapeutic approach for pulmonary hypertension in the era of personalised medicine

Pulmonary hypertension (PH) is a fatal disease, defined as a mean pulmonary artery pressure ≥ 25 mm Hg. It is caused, in part, by mitochondrial dysfunction. Among the various biological therapies proposed to rescue mitochondrial dysfunction, evidence going back as far as 2009, suggests that mitochondrial transplantation is an alternative. Although scant, recent PH findings and other literature supports a role for mitochondrial transplantation as a therapeutic approach in the context of PH. In experimental models of PH, it confers beneficial effects that include reduced pulmonary vasoconstriction, reduced pulmonary vascular remodelling, and improved right ventricular function. It also reduces the proliferation of pulmonary artery smooth muscle cells. However, first, we must understand that more research is needed before mitochondrial transplantation can be considered an effective therapy in the clinical setting, as many of the mechanisms or potential long-term risks are still unknown. Second, the current challenges of mitochondrial transplantation are surmountable and should not deter researchers from further investigating its effectiveness and trying to overcome these challenges in creative ways.

Upregulation of IRF9 Contributes to Pulmonary Artery Smooth Muscle Cell Proliferation During Pulmonary Arterial Hypertension

Abnormal proliferation of pulmonary artery smooth muscle cells (PASMCs) is a critical pathological feature in the pathogenesis of pulmonary arterial hypertension (PAH), but the regulatory mechanisms remain largely unknown. Herein, we demonstrated that interferon regulatory factor 9 (IRF9) accelerated PASMCs proliferation by regulating Prohibitin 1 (PHB1) expression and the AKT-GSK3β signaling pathway. Compared with control groups, the rats treated with chronic hypoxia (CH), monocrotaline (MCT) or sugen5416 combined with chronic hypoxia (SuHx), and mice challenged with CH had significantly thickened pulmonary arterioles and hyperproliferative PASMCs. More importantly, the protein level of IRF9 was found to be elevated in the thickened medial wall of the pulmonary arterioles in all of these PAH models. Notably, overexpression of IRF9 significantly promoted the proliferation of rat and human PASMCs, as evidenced by increased cell counts, EdU-positive cells and upregulated biomarkers of cell proliferation. In contrast, knockdown of IRF9 suppressed the proliferation of rat and human PASMCs. Mechanistically, IRF9 directly restrained PHB1 expression and interacted with AKT to inhibit the phosphorylation of AKT at thr308 site, which finally led to mitochondrial dysfunction and PASMC proliferation. Unsurprisingly, MK2206, a specific inhibitor of AKT, partially reversed the PASMC proliferation inhibited by IRF9 knockdown. Thus, our results suggested that elevation of IRF9 facilitates PASMC proliferation by regulating PHB1 expression and AKT signaling pathway to affect mitochondrial function during the development of PAH, which indicated that targeting IRF9 may serve as a novel strategy to delay the pathological progression of PAH.

Requirements for successful mitochondrial transplantation

Maintenance of mitochondrial oxidative phosphorylation capacity and other mitochondrial functions are essential for the prevention of mitochondrial dysfunction-related diseases such as neurodegenerative, cardiovascular, and liver diseases. To date, no well-known treatment modality has been developed to prevent or reduce mitochondrial dysfunction. However, a novel approach that transplants fully functional mitochondria directly into defective cells has recently caught the attention of scientists. In this review, we provide an overview of the cell/tissue source of the mitochondria to prompt cell regeneration or tissue repair in vitro and in vivo applications. The animal and human models entail that effective procedures should be used in the isolation and confirmation of mitochondrial membrane potential and function. We believe that these procedures for mitochondrial transplantation for tissue or cell culture will confirm intact, viable, and free from contamination isolated mitochondria from the appropriate sources.

Mitotherapy as a Novel Therapeutic Strategy for Mitochondrial Diseases

BACKGROUND

The mitochondrion is a multi-functional organelle that is mainly responsible for energy supply in the mammalian cells. Over 100 human diseases are attributed to mitochondrial dysfunction. Mitochondrial therapy (mitotherapy) aims to transfer functional exogenous mitochondria into mitochondria-defective cells for recovery of the cell viability and consequently, prevention of the disease progress.

OBJECTIVE

The review summarizes the evidence on exogenous mitochondria that can directly enter mammalian cells for disease therapy following local and intravenous administration, and suggests that when healthy cells donate their mitochondria to damaged cells, the mitochondrial transfer between cells serve as a new mode of cell rescue. Then the transferred mitochondria play their roles in recipient cells, including energy production and maintenance of cell function.

CONCLUSION

Mitotherapy makes the of modulation of cell survival possible, and it would be a potential therapeutic strategy for mitochondrial diseases.

Novel molecular insights and public omics data in pulmonary hypertension

Pulmonary hypertension is a rare disease with high morbidity and mortality which mainly affects women of reproductive age. Despite recent advances in understanding the pathogenesis of pulmonary hypertension, the high heterogeneity in the presentation of the disease among different patients makes it difficult to make an accurate diagnosis and to apply this knowledge to effective treatments. Therefore, new studies are required to focus on translational and personalized medicine to overcome the lack of specificity and efficacy of current management. Here, we review the majority of public databases storing 'omics' data of pulmonary hypertension studies, from animal models to human patients. Moreover, we review some of the new molecular mechanisms involved in the pathogenesis of pulmonary hypertension, including non-coding RNAs and the application of 'omics' data to understand this pathology, hoping that these new approaches will provide insights to guide the way to personalized diagnosis and treatment.

Mitochondria Donation by Mesenchymal Stem Cells: Current Understanding and Mitochondria Transplantation Strategies

The phenomenon of mitochondria donation is found in various tissues of humans and animals and is attracting increasing attention. To date, numerous studies have described the transfer of mitochondria from stem cells to injured cells, leading to increased ATP production, restoration of mitochondria function, and rescue of recipient cells from apoptosis. Mitochondria transplantation is considered as a novel therapeutic approach for the treatment of mitochondrial diseases and mitochondrial function deficiency. Mitochondrial dysfunction affects cells with high energy needs such as neural, skeletal muscle, heart, and liver cells and plays a crucial role in type 2 diabetes, as well as Parkinson's, Alzheimer's diseases, ischemia, stroke, cancer, and age-related disorders. In this review, we summarize recent findings in the field of mitochondria donation and mechanism of mitochondria transfer between cells. We review the existing clinical trials and discuss advantages and disadvantages of mitochondrial transplantation strategies based on the injection of stem cells, isolated functional mitochondria, or EVs containing mitochondria.

Intercellular Mitochondria Transfer to Macrophages Regulates White Adipose Tissue Homeostasis and Is Impaired in Obesity

Recent studies suggest that mitochondria can be transferred between cells to support the survival of metabolically compromised cells. However, whether intercellular mitochondria transfer occurs in white adipose tissue (WAT) or regulates metabolic homeostasis in vivo remains unknown. We found that macrophages acquire mitochondria from neighboring adipocytes in vivo and that this process defines a transcriptionally distinct macrophage subpopulation. A genome-wide CRISPR-Cas9 knockout screen revealed that mitochondria uptake depends on heparan sulfates (HS). High-fat diet (HFD)-induced obese mice exhibit lower HS levels on WAT macrophages and decreased intercellular mitochondria transfer from adipocytes to macrophages. Deletion of the HS biosynthetic gene Ext1 in myeloid cells decreases mitochondria uptake by WAT macrophages, increases WAT mass, lowers energy expenditure, and exacerbates HFD-induced obesity in vivo. Collectively, this study suggests that adipocytes and macrophages employ intercellular mitochondria transfer as a mechanism of immunometabolic crosstalk that regulates metabolic homeostasis and is impaired in obesity.

Mitochondrial Transplantation: A Critical Analysis

"Mitochondrial transplantation" refers to a procedure for introducing isolated mitochondria into a damaged area of a heart or other organ. A considerable amount of data has been accumulated on the therapeutic effects of "mitochondrial transplantation" in animals with ischemic heart damage. In 2017, the first attempts were made to apply this procedure in a clinic. The authors of the method suggest that exogenous mitochondria penetrate into cardiomyocytes, retaining functional activity, and compensate for impaired energy output of endogenous mitochondria. This hypothesis contradicts the well-known fact of loss of mitochondrial functions in the presence of high concentrations of Ca2+, which are characteristic of the extracellular medium. This review critically considers the possible mechanisms of the therapeutic effect of "mitochondrial transplantation".

Mitochondrial Transplantation for Ischemia Reperfusion Injury

Mitochondrial transplantation is a novel therapeutic intervention to treat ischemia-reperfusion-related disorders. This approach uses replacement of native mitochondria with viable, respiration-competent mitochondria isolated from non-ischemic tissue obtained from the patient's own body, to overcome the many deleterious effects of ischemia-reperfusion injury on native mitochondria. The safety and efficacy of this methodology has been demonstrated in cell culture, animal models and has been shown to be safe and efficacious in a phase I clinical trial in pediatric cardiac patients with ischemia-reperfusion injury. These studies have demonstrated that mitochondrial transplantation rescues myocardial cellular viability and significantly enhances postischemic myocardial function following ischemia-reperfusion injury. Herein, we describe methodologies for the delivery of isolated mitochondria.

Phenylalanine induces pulmonary hypertension through calcium-sensing receptor activation

Phenylalanine levels are associated with pulmonary hypertension in metabolic profiling clinical studies. However, the pathophysiological role of phenylalanine on pulmonary circulation is still unclear. We experimentally addressed the direct impact of phenylalanine on pulmonary circulation in rats and explored the underlying molecular pathway. Phenylalanine was injected intraperitoneally into Sprague-Dawley rats (400 mg/100 g body wt) as a single dose or daily in a chronic manner for 2, 3, and 4 wk. Chronic injection of phenylalanine induced pulmonary hypertension with time-dependent severity, evidenced by elevated pulmonary artery pressure and pulmonary vascular resistance as well as pulmonary artery and right ventricular hypertrophy. Using tandem mass spectrometry analysis, we found a quick twofold increase in blood level of phenylalanine 2 h following injection. This increase led to a significant accumulation of phenylalanine in lung after 4 h, which remained sustained at up to a threefold increase after 4 wk. In addition, a cellular thermal shift assay with lung tissues from phenylalanine-injected rats revealed the binding of phenylalanine to the calcium-sensing receptor (CaSR). In vitro experiments with cultured pulmonary arterial smooth muscle cells showed that phenylalanine activated CaSR, as indicated by an increase in intracellular calcium content, which was attenuated or diminished by the inhibition or knockdown of CaSR. Finally, the global knockout or lung-specific knockdown of CaSR significantly attenuated phenylalanine-induced pulmonary hypertension. Chronic phenylalanine injection induces pulmonary hypertension through binding to CaSR and its subsequent activation. Here, we demonstrate a pathophysiological role of phenylalanine in pulmonary hypertension through the CaSR. This study provides a novel animal model for pulmonary hypertension and reveals a potentially clinically significant role for this metabolite in human pulmonary hypertension as a marker, a mediator of disease, and a possible therapeutic target.

Mitochondrial transplantation enhances murine lung viability and recovery after ischemia-reperfusion injury

The most common cause of acute lung injury is ischemia-reperfusion injury (IRI), during which mitochondrial damage occurs. We have previously demonstrated that mitochondrial transplantation is an efficacious therapy to replace or augment mitochondria damaged by IRI, allowing for enhanced muscle viability and function in cardiac tissue. Here, we investigate the efficacy of mitochondrial transplantation in a murine lung IRI model using male C57BL/6J mice. Transient ischemia was induced by applying a microvascular clamp on the left hilum for 2 h. Upon reperfusion mice received either vehicle or vehicle-containing mitochondria either by vascular delivery (Mito V) through the pulmonary artery or by aerosol delivery (Mito Neb) via the trachea (nebulization). Sham control mice underwent thoracotomy without hilar clamping and were ventilated for 2 h before returning to the cage. After 24 h recovery, lung mechanics were assessed and lungs were collected for analysis. Our results demonstrated that at 24 h of reperfusion, dynamic compliance and inspiratory capacity were significantly increased and resistance, tissue damping, elastance, and peak inspiratory pressure (Mito V only) were significantly decreased (P < 0.05) in Mito groups as compared with their respective vehicle groups. Neutrophil infiltration, interstitial edema, and apoptosis were significantly decreased (P < 0.05) in Mito groups as compared with vehicles. No significant differences in cytokines and chemokines between groups were shown. All lung mechanics results in Mito groups except peak inspiratory pressure in Mito Neb showed no significant differences (P > 0.05) as compared with Sham. These results conclude that mitochondrial transplantation by vascular delivery or nebulization improves lung mechanics and decreases lung tissue injury.

Mitochondria transfer from mesenchymal stem cells structurally and functionally repairs renal proximal tubular epithelial cells in diabetic nephropathy in vivo

The underlying therapeutic mechanism of renal tubular epithelium repair of diabetic nephropathy (DN) by bone marrow-derived mesenchymal stem cells (BM-MSCs) has not been fully elucidated. Recently, mitochondria (Mt) transfer was reported as a novel action of BM-MSCs to rescue injured cells. We investigated Mt transfer from systemically administered BM-MSCs to renal proximal tubular epithelial cells (PTECs) in streptozotocin (STZ)-induced diabetic animals. BM-MSCs also transferred their Mt to impaired PTECs when co-cultured in vitro, which suppressed apoptosis of impaired PTECs. Additionally, BM-MSC-derived isolated Mt enhanced the expression of mitochondrial superoxide dismutase 2 and Bcl-2 expression and inhibited reactive oxygen species (ROS) production in vitro. Isolated Mt also inhibited nuclear translocation of PGC-1α and restored the expression of megalin and SGLT2 under high glucose condition (HG) in PTECs. Moreover, isolated Mt directly injected under the renal capsule of STZ rats improved the cellular morphology of STZ-PTECs, and the structure of the tubular basement membrane and brush border in vivo. This study is the first to show Mt transfer from systemically administered BM-MSCs to damaged PTECs in vivo, and the first to investigate mechanisms underlying the potential therapeutic effects of Mt transfer from BM-MSCs in DN.

HMGB1 is mechanistically essential in the development of experimental pulmonary hypertension

Pulmonary hypertension (PH) is a mortal disease featuring pulmonary vascular constriction and remodeling, right heart failure, and eventual death. Several reports showed that high-mobility group box 1 (HMGB1) appears to be critical for the development of PH; the underlying mechanism, however, has not been revealed. Experiments in the present study demonstrated that HMGB1 levels were elevated in the lung tissue and blood plasma of rats after chronic hypoxia exposure and monocrotaline treatment. HMGB1 was originally located within the nucleus and translocated to the cytoplasm of pulmonary artery smooth muscle cells (PASMCs) upon hypoxia exposure, a process that appeared to be mediated by endogenous H₂O₂. Exposure to HMGB1 mobilized calcium signaling in PASMCs, a response that was attenuated by extracellular Ca²⁺ removal, Toll-like receptor 4 (TLR4) inhibition by TAK-242, or transient receptor potential channel (TRPC) suppression with 2-aminoethoxydiphenyl borate (2-APB) and SKF-96365. The sustained phosphorylation of the Akt pathway modulated HMGB1-induced migration of PASMCs. The blockage of HMGB1 with glycyrrhizin or anti-HMGB1 neutralizing antibody attenuated lung inflammation and PH establishment in rats after hypoxia exposure and monocrotaline treatment. The above findings reveal the mechanistic importance of HMGB1 in PH through TLR4- and TRPC-associated Ca²⁺ influx and Akt phosphorylation-driven PASMC migration.

Pathobiology, pathology and genetics of pulmonary hypertension: Update from the Cologne Consensus Conference 2018

The European guidelines, which focus on clinical aspects of pulmonary hypertension (PH), provide only minimal information about the pathophysiological concepts of PH. Here, we review this topic in greater detail, focusing on specific aspects in the pathobiology, pathology and genetics, which include mechanisms of vascular inflammation, the role of transcription factors, ion channels/ion channel diseases, hypoxic pulmonary vasoconstriction, genetics/epigenetics, metabolic dysfunction, and the potential future role of histopathology of PH in the modern era of PH therapy. In addition to new insights in the pathobiology of this disease, this working group of the Cologne Consensus Conference also highlights novel concepts and potential new therapeutic targets to further improve the treatment options in PAH.

Muscle-derived autologous mitochondrial transplantation: A novel strategy for treating cerebral ischemic injury

The available evidence showed that mitochondrial transfer by releasing the extracellular vesicles containing mitochondria from astrocytes to neurons exerted a neuroprotective effect after stroke. Whether extracellular mitochondrial replenishment could rescue the tissues from cerebral ischemic injury still needs to be explored completely. It was hypothesized that the augmentation of mitochondrial damage after cerebral ischemia could be resolved by timely replenishment of exogenous mitochondria. A stroke model of middle cerebral artery occlusion (MCAO) was used in this study to verify this hypothesis. This study found that the number of extracellular mitochondria increased in rat cerebrospinal fluid after MCAO, and a higher proportion of mitochondria were associated with good neurological outcomes. Following 90-min ischemia, autologously derived mitochondria (isolated from autologous pectoralis major) or vehicle alone was infused directly into the lateral ventricles, and the rats were allowed to recover for 4 weeks. A plenty of infused mitochondria were found to be distributed in the boundary and ischemic penumbra areas. Furthermore, the transplantation of mitochondria reduced cellular oxidative stress and apoptosis, attenuated reactive astrogliosis, and promoted neurogenesis after stroke. Moreover, the transplantation of mitochondria decreased brain infarct volume and reversed neurological deficits. The findings suggested that the delivery of mitochondria through the lateral ventricles resulted in their widespread distribution throughout the brain and exerted a neuroprotective effect after ischemia-reperfusion injury.

COMP-prohibitin 2 interaction maintains mitochondrial homeostasis and controls smooth muscle cell identity

Vascular smooth muscle cells (VSMCs) are highly phenotypically plastic, and loss of the contractile phenotype in VSMCs has been recognized at the early onset of the pathology of a variety of vascular diseases. However, the endogenous regulatory mechanism to maintain contractile phenotype in VSMCs remains elusive. Moreover, little has been known about the role of the mitochondrial bioenergetics in terms of VSMC homeostasis. Herein, we asked if glycoprotein COMP (Cartilage oligomeric matrix protein) is involved in mitochondrial bioenergetics and therefore regulates VSMCs homeostasis. By using fluorescence assay, subcellular western blot and liquid chromatography tandem mass spectrometry analysis, we found that extracellular matrix protein COMP unexpectedly localized within mitochondria. Further mitochondrial transplantation revealed that both mitochondrial and non-mitochondrial COMP maintained VSMC identity. Moreover, microarray analysis revealed that COMP deficiency impaired mitochondrial oxidative phosphorylation in VSMCs. Further study confirmed that COMP deficiency caused mitochondrial oxidative phosphorylation dysfunction accompanied by morphological abnormality. Moreover, the interactome of mitochondrial COMP revealed that COMP interacted with prohibitin 2, and COMP-prohibitin 2 interaction maintained mitochondrial homeostasis. Additionally, disruption of COMP-prohibitin 2 interaction caused VSMC dedifferentiation in vitro and enhanced the neointima formation post rat carotid artery injury in vivo. In conclusion, COMP-prohibitin 2 interaction in mitochondria plays an important role in maintaining the contractile phenotype of VSMCs by regulating mitochondrial oxidative phosphorylation. Maintaining the homeostasis of mitochondrial respiration through COMP-prohibitin 2 interaction may shed light on prevention of vascular disease.

Mitochondrial dysfunction and pulmonary hypertension: cause, effect, or both

Pulmonary hypertension describes a heterogeneous disease defined by increased pulmonary artery pressures, and progressive increase in pulmonary vascular resistance due to pathologic remodeling of the pulmonary vasculature involving pulmonary endothelial cells, pericytes, and smooth muscle cells. This process occurs under various conditions, and although these populations vary, the clinical manifestations are the same: progressive dyspnea, increases in right ventricular (RV) afterload and dysfunction, RV-pulmonary artery uncoupling, and right-sided heart failure with systemic circulatory collapse. The overall estimated 5-yr survival rate is 72% in highly functioning patients, and as low as 28% for those presenting with advanced symptoms. Metabolic theories have been suggested as underlying the pathogenesis of pulmonary hypertension with growing evidence of the role of mitochondrial dysfunction involving the major proteins of the electron transport chain, redox-related enzymes, regulators of the proton gradient and calcium homeostasis, regulators of apoptosis, and mitophagy. There remain more studies needed to characterize mitochondrial dysfunction leading to impaired vascular relaxation, increase proliferation, and failure of regulatory mechanisms. The effects on endothelial cells and resulting interactions with their microenvironment remain uncharted territory for future discovery. Additionally, on the basis of observations that the "plexigenic lesions" of pulmonary hypertension resemble the unregulated proliferation of tumor cells, similarities between cancer pathobiology and pulmonary hypertension have been drawn, suggesting interactions between mitochondria and angiogenesis. Recently, mitochondria targeting has become feasible, which may yield new therapeutic strategies. We present a state-of-the-art review of the role of mitochondria in both the pathobiology of pulmonary hypertension and potential therapeutic targets in pulmonary vascular processes.

Hypoxia selectively upregulates cation channels and increases cytosolic [Ca2+] in pulmonary, but not coronary, arterial smooth muscle cells

Ca²⁺ signaling, particularly the mechanism via store-operated Ca²⁺ entry (SOCE) and receptor-operated Ca²⁺ entry (ROCE), plays a critical role in the development of acute hypoxia-induced pulmonary vasoconstriction and chronic hypoxia-induced pulmonary hypertension. This study aimed to test the hypothesis that chronic hypoxia differentially regulates the expression of proteins that mediate SOCE and ROCE [stromal interacting molecule (STIM), Orai, and canonical transient receptor potential channel TRPC6] in pulmonary (PASMC) and coronary (CASMC) artery smooth muscle cells. The resting cytosolic [Ca²⁺] ([Ca²⁺]_cyt) and the stored [Ca²⁺] in the sarcoplasmic reticulum were not different in CASMC and PASMC. Seahorse measurement showed a similar level of mitochondrial bioenergetics (basal respiration and ATP production) between CASMC and PASMC. Glycolysis was significantly higher in PASMC than in CASMC. The amplitudes of cyclopiazonic acid-induced SOCE and OAG-induced ROCE in CASMC are slightly, but significantly, greater than in PASMC. The frequency and the area under the curve of Ca²⁺ oscillations induced by ATP and histamine were also larger in CASMC than in PASMC. Na⁺/Ca²⁺ exchanger-mediated increases in [Ca²⁺]_cyt did not differ significantly between CASMC and PASMC. The basal protein expression levels of STIM1/2, Orai1/2, and TRPC6 were higher in CASMC than in PASMC, but hypoxia (3% O₂ for 72 h) significantly upregulated protein expression levels of STIM1/STIM2, Orai1/Orai2, and TRPC6 and increased the resting [Ca²⁺]_cyt only in PASMC, but not in CASMC. The different response of essential components of store-operated and receptor-operated Ca²⁺ channels to hypoxia is a unique intrinsic property of PASMC, which is likely one of the important explanations why hypoxia causes pulmonary vasoconstriction and induces pulmonary vascular remodeling, but causes coronary vasodilation.

Mitochondrial Transplantation in Myocardial Ischemia and Reperfusion Injury

Ischemic heart disease remains the leading cause of death worldwide. Mitochondria are the power plant of the cardiomyocyte, generating more than 95% of the cardiac ATP. Complex cellular responses to myocardial ischemia converge on mitochondrial malfunction which persists and increases after reperfusion, determining the extent of cellular viability and post-ischemic functional recovery. In a quest to ameliorate various points in pathways from mitochondrial damage to myocardial necrosis, exhaustive pharmacologic and genetic tools have targeted various mediators of ischemia and reperfusion injury and procedural techniques without applicable success. The new concept of replacing damaged mitochondria with healthy mitochondria at the onset of reperfusion by auto-transplantation is emerging not only as potential therapy of myocardial rescue, but as gateway to a deeper understanding of mitochondrial metabolism and function. In this chapter, we explore the mechanisms of mitochondrial dysfunction during ischemia and reperfusion, current developments in the methodology of mitochondrial transplantation, mechanisms of cardioprotection and their clinical implications.

Recent advances in oxygen sensing and signal transduction in hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is a physiological reaction, which adapts lung perfusion to regional ventilation and optimizes gas exchange. Impaired HPV may cause systemic hypoxemia, while generalized HPV contributes to the development of pulmonary hypertension. The triggering mechanisms underlying HPV are still not fully elucidated. Several hypotheses are currently under debate, including a possible decrease as well as an increase in reactive oxygen species as a triggering event. Recent findings suggest an increase in the production of reactive oxygen species in pulmonary artery smooth muscle cells by complex III of the mitochondrial electron transport chain and occurrence of oxygen sensing at complex IV. Other essential components are voltage-dependent potassium and possibly L-type, transient receptor potential channel 6, and transient receptor potential vanilloid 4 channels. The release of arachidonic acid metabolites appears also to be involved in HPV regulation. Further investigation of the HPV mechanisms will facilitate the development of novel therapeutic strategies for the treatment of HPV-related disorders.

Hypoxia-Induced Mitogenic Factor Acts as a Nonclassical Ligand of Calcium-Sensing Receptor, Therapeutically Exploitable for Intermittent Hypoxia-Induced Pulmonary Hypertension

Hypoxia-induced mitogenic factor (HIMF) is an inflammatory cytokine playing important role(s) in the development of hypoxic pulmonary hypertension. The molecular target mediating HIMF-stimulated downstream events remains unclear. The coimmunoprecipitation screen identified extracellular calcium-sensing receptor (CaSR) as the binding partner for HIMF in pulmonary artery smooth muscle cells. The yeast 2-hybrid assay then revealed the binding of HIMF to the intracellular, not the extracellular, domain of extracellular CaSR. The binding of HIMF enhanced the activity of extracellular CaSR and mediated hypoxia-evoked proliferation of pulmonary artery smooth cells and the development of pulmonary vascular remodeling and pulmonary hypertension, all of which was specifically attenuated by a synthesized membrane-permeable peptide flanking the core amino acids of the intracellular binding domain of extracellular CaSR. Thus, HIMF induces pulmonary hypertension as a nonclassical ligand of extracellular CaSR, and the binding motif of extracellular CaSR can be therapeutically exploitable.