Inhibition of Kir2.1 channel-induced depolarization promotes cell biological activity and differentiation by modulating autophagy in late endothelial progenitor cells

Advancements in the study of inward rectifying potassium channels on vascular cells

Inward rectifier potassium channels (Kir channels) exist in a variety of cells and are involved in maintaining resting membrane potential and signal transduction in most cells, as well as connecting metabolism and membrane excitability of body cells. It is closely related to normal physiological functions of body and the occurrence and development of some diseases. Although the functional expression of Kir channels and their role in disease have been studied, they have not been fully elucidated. In this paper, the functional expression of Kir channels in vascular endothelial cells and smooth muscle cells and their changes in disease states were reviewed, especially the recent research progress of Kir channels in stem cells was introduced, in order to have a deeper understanding of Kir channels in vascular tissues and provide new ideas and directions for the treatment of related ion channel diseases.

Inhibition of KIR2.1 decreases pulmonary artery smooth muscle cell proliferation and migration

The investigation of effective therapeutic drugs for pulmonary hypertension (PH) is critical. KIR2.1 plays crucial roles in regulating cell proliferation and migration, and vascular remodeling. However, researchers have not yet clearly determined whether KIR2.1 participates in the proliferation and migration of pulmonary artery smooth muscle cells (PASMCs) and its role in pulmonary vascular remodeling (PVR) also remains elusive. The present study aimed to examine whether KIR2.1 alters PASMC proliferation and migration, and participates in PVR, as well as to explore its mechanisms of action. For the in vivo experiment, a PH model was established by intraperitoneally injecting Sprague-Dawley rats monocrotaline (MCT). Hematoxylin and eosin staining revealed evidence of PVR in the rats with PH. Immunofluorescence staining and western blot analysis revealed increased levels of the KIR2.1, osteopontin (OPN) and proliferating cell nuclear antigen (PCNA) proteins in pulmonary blood vessels and lung tissues following exposure to MCT, and the TGF-β1/SMAD2/3 signaling pathway was activated. For the in vitro experiments, the KIR2.1 inhibitor, ML133, or the TGF-β1/SMAD2/3 signaling pathway blocker, SB431542, were used to pre-treat human PASMCs (HPASMCs) for 24 h, and the cells were then treated with platelet-derived growth factor (PDGF)-BB for 24 h. Scratch and Transwell assays revealed that PDGF-BB promoted cell proliferation and migration. Immunofluorescence staining and western blot analysis demonstrated that PDGF-BB upregulated OPN and PCNA expression, and activated the TGF-β1/SMAD2/3 signaling pathway. ML133 reversed the proliferation and migration induced by PDGF-BB, inhibited the expression of OPN and PCNA, inhibited the TGF-β1/SMAD2/3 signaling pathway, and reduced the proliferation and migration of HPASMCs. SB431542 pre-treatment also reduced cell proliferation and migration; however, it did not affect KIR2.1 expression. On the whole, the results of the present study demonstrate that KIR2.1 regulates the TGF-β1/SMAD2/3 signaling pathway and the expression of OPN and PCNA proteins, thereby regulating the proliferation and migration of PASMCs and participating in PVR.

Slight up-regulation of Kir2.1 channel promotes endothelial progenitor cells to transdifferentiate into a pericyte phenotype by Akt/mTOR/Snail pathway

It was shown that endothelial progenitor cells (EPCs) have bidirectional differentiation potential and thus perform different biological functions. The purpose of this study was to investigate the effects of slight up‐regulation of the Kir2.1 channel on EPC transdifferentiation and the potential mechanism on cell function and transformed cell type. First, we found that the slight up‐regulation of Kir2.1 expression promoted the expression of the stem cell stemness factors ZFX and NS and inhibited the expression of senescence‐associated β‐galactosidase. Further studies showed the slightly increased expression of Kir2.1 could also improve the expression of pericyte molecular markers NG2, PDGFRβ and Desmin. Moreover, adenovirus‐mediated Kir2.1 overexpression had an enhanced contractile response to norepinephrine of EPCs. These results suggest that the up‐regulated expression of the Kir2.1 channel promotes EPC transdifferentiation into a pericyte phenotype. Furthermore, the mechanism of EPC transdifferentiation to mesenchymal cells (pericytes) was found to be closely related to the channel functional activity of Kir2.1 and revealed that this channel could promote EPC EndoMT by activating the Akt/mTOR/Snail signalling pathway. Overall, this study suggested that in the early stage of inflammatory response, regulating the Kir2.1 channel expression affects the biological function of EPCs, thereby determining the maturation and stability of neovascularization.

Impaired Hippocampal Neurovascular Coupling in a Mouse Model of Alzheimer's Disease

Alzheimer’s disease (AD), the most common form of dementia, is characterized by neuronal degeneration and cerebrovascular dysfunction. Increasing evidence indicates that cerebrovascular dysfunction may be a key or an aggravating pathogenic factor in AD. This emphasizes the importance to investigate the tight coupling between neuronal activity and cerebral blood flow (CBF) termed neurovascular coupling (NVC). NVC depends on all cell types of the neurovascular unit within which astrocytes are important players in the progression of AD. Hence, the objective of this study was to characterize the hippocampal NVC in a mouse model of AD. Hippocampal NVC was studied in 6-month-old amyloid-beta precursor protein (APP) transgenic mice and their corresponding wild-type littermates using in vivo laser Doppler flowmetry to measure CBF in area CA1 of the hippocampus in response to Schaffer collaterals stimulation. Ex vivo two-photon microscopy experiments were performed to determine astrocytic Ca²⁺ and vascular responses to electrical field stimulation (EFS) or caged Ca²⁺ photolysis in hippocampal slices. Neuronal synaptic transmission, astrocytic endfeet Ca²⁺ in correlation with reactive oxygen species (ROS), and vascular reactivity in the presence or absence of Tempol, a mimetic of superoxide dismutase, were further investigated using electrophysiological, caged Ca²⁺ photolysis or pharmacological approaches. Whisker stimulation evoked-CBF increases and ex vivo vascular responses to EFS were impaired in APP mice compared with their age-matched controls. APP mice were also characterized by decreased basal synaptic transmission, a shorter astrocytic Ca²⁺ increase, and altered vascular response to elevated perivascular K⁺. However, long-term potentiation, astrocytic Ca²⁺ amplitude in response to EFS, together with vascular responses to nitric oxide remained unchanged. Importantly, we found a significantly increased Ca²⁺ uncaging-induced ROS production in APP mice. Tempol prevented the vascular response impairment while normalizing astrocytic Ca²⁺ in APP mice. These findings suggest that NVC is altered at many levels in APP mice, at least in part through oxidative stress. This points out that therapies against AD should include an antioxidative component to protect the neurovascular unit.

Combined NOX/ROS/PKC Signaling Pathway and Metabolomic Analysis Reveals the Mechanism of TRAM34-Induced Endothelial Progenitor Cell Senescence

It has been shown that the KCa3.1 channel-specific blocker, TRAM34, is a promising antiatherosclerosis (AS) agent, but its side effects restrict its clinical application. Notably, its effect on endothelial progenitor cells (EPCs) is unclear. We aim to unravel the effect of TRAM34 on EPCs and identify the underlying mechanism. Rats were injected intraperitoneally with TRAM34, and EPCs were isolated from bone marrow. The gene and protein levels of corresponding factors were detected by real-time PCR, enzyme-linked immunosorbent assay, western blotting, and fluorescence-activated cell sorting. Liquid chromatography-tandem mass spectrometry (LC-MS) was applied to detect metabolite differences. We showed that when rats were treated with TRAM34 in vivo, colony formation and proliferation of early EPCs were reduced, but their senescence and apoptosis were enhanced. Moreover, TRAM34 enhanced NOX activity, promoted an increase in intracellular ROS levels, increased PKC expression, and subsequently promoted EPC senescence, which is unfavorable for EPC angiogenesis in vivo and in vitro. Combining these results with LC-MS data, we found that TRAM34 significantly promoted pyrimidine and purine metabolism, leading to cellular senescence. Furthermore, the NOX inhibitor, Setanaxib, enhanced antioxidant metabolic pathways, especially S-adenosylmethioninamine (SAM) metabolism, to exert an antisenescence effect. Finally, we confirmed that SAM alleviates TRAM34-induced cellular senescence, suggesting an efficient approach to improve the quality of endogenous EPCs. This study reveals the mechanism of TRAM34-induced EPC senescence, providing a solution for the extended application of KCa3.1 inhibitor in AS.

Next-generation inward rectifier potassium channel modulators: discovery and molecular pharmacology

Inward rectifying potassium (Kir) channels play important roles in both excitable and nonexcitable cells of various organ systems and could represent valuable new drug targets for cardiovascular, metabolic, immune, and neurological diseases. In nonexcitable epithelial cells of the kidney tubule, for example, Kir1.1 (KCNJ1) and Kir4.1 (KCNJ10) are linked to sodium reabsorption in the thick ascending limb of Henle's loop and distal convoluted tubule, respectively, and have been explored as novel-mechanism diuretic targets for managing hypertension and edema. G protein-coupled Kir channels (Kir3) channels expressed in the central nervous system are critical effectors of numerous signal transduction pathways underlying analgesia, addiction, and respiratory-depressive effects of opioids. The historical dearth of pharmacological tool compounds for exploring the therapeutic potential of Kir channels has led to a molecular target-based approach using high-throughput screen (HTS) of small-molecule libraries and medicinal chemistry to develop "next-generation" Kir channel modulators that are both potent and specific for their targets. In this article, we review recent efforts focused specifically on discovery and improvement of target-selective molecular probes. The reader is introduced to fluorescence-based thallium flux assays that have enabled much of this work and then provided with an overview of progress made toward developing modulators of Kir1.1 (VU590, VU591), Kir2.x (ML133), Kir3.X (ML297, GAT1508, GiGA1, VU059331), Kir4.1 (VU0134992), and Kir7.1 (ML418). We discuss what is known about the small molecules' molecular mechanisms of action, in vitro and in vivo pharmacology, and then close with our view of what critical work remains to be done.

Ion Channels and Transporters in Autophagy

Ion exchange between intracellular and extracellular spaces is the basic mechanism for controlling cell metabolism and signal transduction. This process is mediated by ion channels and transporters on the plasma membrane, or intracellular membranes that surround various organelles, in response to environmental stimuli. Macroautophagy (hereafter referred to as autophagy) is one of the lysosomal-dependent degradation pathways that maintains homeostasis through the degradation and recycling of cellular components (e.g., dysfunctional proteins and damaged organelles). Although autophagy-related (ATG) proteins play a central role in regulating the formation of autophagy-related member structures (e.g., phagophores, autophagosomes, and autolysosomes), the autophagic process also involves changes in expression and function of ion channels and transporters. Here we discuss current knowledge of the mechanisms that regulate autophagy in mammalian cells, with special attention to the ion channels and transporters. We also highlight prospects for the development of drugs targeting ion channels and transporters in autophagy.

The effects of membrane potential and extracellular matrix composition on vascular differentiation of cardiac progenitor cells

Historically, the field of tissue engineering has been adept at modulating the chemical and physical microenvironment. This approach has yielded significant progress, but it is imperative to further integrate our understanding of other fundamental cell signaling paradigms into tissue engineering methods. Bioelectric signaling has been demonstrated to be a vital part of tissue development, regeneration, and function across organ systems and the extracellular matrix is known to alter the bioelectric properties of cells. Thus, there is a need to bolster our understanding of how matrix and bioelectric signals interact to drive cell phenotype. We examine how cardiac progenitor cell differentiation is altered by simultaneous changes in both resting membrane potential and extracellular matrix composition. Pediatric c-kit⁺ cardiac progenitor cells were differentiated on fetal or adult cardiac extracellular matrix while being treated with drugs that alter resting membrane potential. Smooth muscle gene expression was increased with depolarization and decreased with hyperpolarization while endothelial and cardiac expression were unchanged. Early smooth muscle protein expression is modified by matrix developmental age, with fetal ECM appearing to amplify the effects of resting membrane potential. Thus, combining matrix composition and bioelectric signaling represents a potential alternative for guiding cell behavior in tissue engineering and regenerative medicine.

Oscillating shear stress mediates mesenchymal transdifferentiation of EPCs by the Kir2.1 channel

Although endothelial progenitor cells (EPCs) are considered to be an essential source of vascular endothelial repair, their bidirectional differentiation determines that they play a double-edged role in the restoration of endothelial injury. In this research, we investigated the effect of Kir2.1 ion channel on the transdifferentiation of endothelial progenitor cells (EPCs) under the oscillating shear stress (OSS) and the molecular mechanisms underlying the pathological vascular remodeling. EPCs were treated with OSS (± 3.5 dynes/cm², 1 Hz) simulated with the parallel flow chamber system. The results have shown that OSS promoted the expression of α-SMA and SM22, markers of mesenchymal cells on EPCs. Moreover, OSS also increased expression of Kir2.1 in EPCs. The down-regulation of Kir2.1 reduced OSS-induced EPC mesenchymal transdifferentiation. The overexpression of Kir2.1 suppressed the angiogenic abilities of EPCs in vitro. In parallel, the overexpression of Kir2.1 on EPCs thickened the carotid tunica intima in rat carotid artery balloon injured model in vivo. Taken together, those data indicated that the OSS could facilitate the transdifferentiation of EPCs by increasing Kir2.1 expression. This study provides a novel insight into the pathogenesis of cardiovascular diseases and gives evidence for Kir2.1 as a potential therapeutic target.