TRPV1 activation mitigates hypoxic injury in mouse cardiomyocytes by inducing autophagy through the AMPK signaling pathway

Targeting TRPs in autophagy regulation and human diseases

Transient receptor potential channels (TRPs) are widely recognized as a group of ion channels involved in various sensory perceptions, such as temperature, taste, pressure, and vision. While macroautophagy (hereafter referred to as autophagy) is primarily regulated by core machinery, the ion exchange mediated by TRPs between intracellular and extracellular compartments, as well as within organelles and the cytoplasm, plays a crucial role in autophagy regulation as an important signaling transduction mechanism. Moreover, certain TRPs can directly interact with autophagy regulatory proteins to participate in autophagy regulation. In this article, we provide an in-depth review of the current understanding of the regulatory mechanisms of autophagy, with a specific focus on TRPs. Furthermore, we highlight the potential prospects for drug development targeting TRPs in autophagy for the treatment of human diseases.

Dual Role of TRPV1 Channels in Cerebral Stroke: An Exploration from a Mechanistic and Therapeutic Perspective

Transient receptor potential vanilloid subfamily member 1 (TRPV1) has been strongly implicated in the pathophysiology of cerebral stroke. However, the exact role and mechanism remain elusive. TPRV1 channels are exclusively present in the neurovascular system and involve many neuronal processes. Numerous experimental investigations have demonstrated that TRPV1 channel blockers or the lack of TRPV1 channels may prevent harmful inflammatory responses during ischemia-reperfusion injury, hence conferring neuroprotection. However, TRPV1 agonists such as capsaicin and some other non-specific TRPV1 activators may induce transient/slight degree of TRPV1 channel activation to confer neuroprotection through a variety of mechanisms, including hypothermia induction, improving vascular functions, inducing autophagy, preventing neuronal death, improving memory deficits, and inhibiting inflammation. Another factor in capsaicin-mediated neuroprotection could be the desensitization of TRPV1 channels. Based on the summarized evidence, it may be plausible to suggest that TPRV1 channels have a dual role in ischemia-reperfusion-induced cerebral injury, and thus, both agonists and antagonists may produce neuroprotection depending upon the dose and duration. The current review summarizes the dual function of TRPV1 in ischemia-reperfusion-induced cerebral injury models, explains its mechanism, and predicts the future.

Mitochondria-associated endoplasmic reticulum membrane (MAM): a dark horse for diabetic cardiomyopathy treatment

Diabetic cardiomyopathy (DCM), an important complication of diabetes mellitus (DM), is one of the most serious chronic heart diseases and has become a major cause of heart failure worldwide. At present, the pathogenesis of DCM is unclear, and there is still a lack of effective therapeutics. Previous studies have shown that the homeostasis of mitochondria and the endoplasmic reticulum (ER) play a core role in maintaining cardiovascular function, and structural and functional abnormalities in these organelles seriously impact the occurrence and development of various cardiovascular diseases, including DCM. The interplay between mitochondria and the ER is mediated by the mitochondria-associated ER membrane (MAM), which participates in regulating energy metabolism, calcium homeostasis, mitochondrial dynamics, autophagy, ER stress, inflammation, and other cellular processes. Recent studies have proven that MAM is closely related to the initiation and progression of DCM. In this study, we aim to summarize the recent research progress on MAM, elaborate on the key role of MAM in DCM, and discuss the potential of MAM as an important therapeutic target for DCM, thereby providing a theoretical reference for basic and clinical studies of DCM treatment.

Activation of transient receptor potential vanilloid 1 ameliorates tau accumulation-induced synaptic damage and cognitive dysfunction via autophagy enhancement

AIMS

The autophagy-lysosomal pathway is important for maintaining cellular proteostasis, while dysfunction of this pathway has been suggested to drive the aberrant intraneuronal accumulation of tau protein, leading to synaptic damage and cognitive impairment. Previous studies have demonstrated that the activation of transient receptor potential vanilloid 1 (TRPV1) by capsaicin has a positive impact on cognition and AD-related biomarkers. However, the effect and mechanism of TPRV1 activation on neuronal tau homeostasis remain elusive.

METHODS

A mouse model of tauopathy was established by overexpressing full-length human tau in the CA3 area. Mice were fed capsaicin diet (0.0125%) or normal diet for 9 weeks. The cognitive ability, synaptic function, tau phosphorylation levels, and autophagy markers were detected. In vitro, capsaicin-induced alterations in cellular autophagy and tau degradation were characterized using two cell models. Besides, various inhibitors were applied to validate the role of TRPV1-mediated autophagy enhancement in tau clearance.

RESULTS

We observed that TRPV1 activation by capsaicin effectively mitigates hippocampal tau accumulation-induced synaptic damages, gliosis, and cognitive impairment in vivo. Capsaicin promotes the degradation of abnormally accumulated tau through enhancing autophagic function in neurons, which is dependent on TRPV1-mediated activation of AMP-activated protein kinase (AMPK) and subsequent inhibition of the mammalian target of rapamycin (mTOR). Blocking AMPK activation abolishes capsaicin-induced autophagy enhancement and tau degradation in neurons.

CONCLUSION

Our findings reveal that capsaicin-induced TRPV1 activation confers neuroprotection by restoring neuronal tau homeostasis via modulating cellular autophagy and provides additional evidence to support the potential of TRPV1 as a therapeutic target for tauopathies.

Transient receptor potential vanilloid type 1: cardioprotective effects in diabetic models

Cardiovascular disease, especially heart failure (HF) is the leading cause of death in patients with diabetes. Individuals with diabetes are prone to a special type of cardiomyopathy called diabetic cardiomyopathy (DCM), which cannot be explained by heart diseases such as hypertension or coronary artery disease, and can contribute to HF. Unfortunately, the current treatment strategy for diabetes-related cardiovascular complications is mainly to control blood glucose levels; nonetheless, the improvement of cardiac structure and function is not ideal. The transient receptor potential cation channel subfamily V member 1 (TRPV1), a nonselective cation channel, has been shown to be universally expressed in the cardiovascular system. Increasing evidence has shown that the activation of TRPV1 channel has a potential protective influence on the cardiovascular system. Numerous studies show that activating TRPV1 channels can improve the occurrence and progression of diabetes-related complications, including cardiomyopathy; however, the specific mechanisms and effects are unclear. In this review, we summarize that TRPV1 channel activation plays a protective role in the heart of diabetic models from oxidation/nitrification stress, mitochondrial function, endothelial function, inflammation, and cardiac energy metabolism to inhibit the occurrence and progression of DCM. Therefore, TRPV1 may become a latent target for the prevention and treatment of diabetes-induced cardiovascular complications.

Morphological study of the postnatal hippocampal development in the TRPV1 knockout mice

Transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel with polymodal sensory function. TRPV1 links to fever, while, according to previous studies on TRPV1 knock-out (KO) mice, the role of the channel in the generation of febrile seizure is debated. In the hippocampal formation, functional TRPV1 channels are expressed by Cajal-Retzius cells, which have a role in guidance of migrating neurons during development. Despite the developmental aspects of febrile seizure as well as of Cajal-Retzius cells, no information is available about the hippocampal development in TRPV1 KO mouse. Therefore, in the present work postnatal development of the hippocampal formation was studied in TRPV1 KO mice. Several morphological characteristics including neuronal positioning and maturation, synaptogenesis and myelination were examined with light microscopy following immunohistochemical detection of protein markers of various neurons, synapses, and myelination. Regarding the cytoarchitectonics, neuronal migration, morphological, and neurochemical maturation, no substantial difference could be detected between TRPV1 KO and wild-type control mice. Our data indicate that synapse formation and myelination occur similarly in TRPV1 KO and in control animals. We have found slightly, but not significantly larger numbers of persisting Cajal-Retzius cells in the KO mice than in controls. Our result strengthens previous suggestion concerning the role of TRPV1 channel in the postnatal apoptotic cell death of Cajal-Retzius cells. However, the fact that the hippocampus of KO mice lacks major developmental abnormalities supports the use of TRPV1 KO in various animal models of diseases and pathological conditions.

The interaction of TRPV1 and lipids: Insights into lipid metabolism

Transient receptor potential vanilloid 1 (TRPV1), a non-selective ligand-gated cation channel with high permeability for Ca²⁺, has received considerable attention as potential therapeutic target for the treatment of several disorders including pain, inflammation, and hyperlipidemia. In particular, TRPV1 regulates lipid metabolism by mechanisms that are not completely understood. Interestingly, TRPV1 and lipids regulate each other in a reciprocal and complex manner. This review surveyed the recent literature dealing with the role of TRPV1 in the hyperlipidemia-associated metabolic syndrome. Besides TRPV1 structure, molecular mechanisms underlying the regulatory effect of TRPV1 on lipid metabolism such as the involvement of uncoupling proteins (UCPs), ATP-binding cassette (ABC) transporters, peroxisome proliferation-activated receptors (PPAR), sterol responsive element binding protein (SREBP), and hypoxia have been discussed. Additionally, this review extends our understanding of the lipid-dependent modulation of TRPV1 activity through affecting both the gating and the expression of TRPV1. The regulatory role of different classes of lipids such as phosphatidylinositol (PI), cholesterol, estrogen, and oleoylethanolamide (OEA), on TRPV1 has also been addressed.

FUCCI-Based Live Imaging Platform Reveals Cell Cycle Dynamics and Identifies Pro-proliferative Compounds in Human iPSC-Derived Cardiomyocytes

One of the major goals in cardiac regeneration research is to replace lost ventricular tissue with new cardiomyocytes. However, cardiomyocyte proliferation drops to low levels in neonatal hearts and is no longer efficient in compensating for the loss of functional myocardium in heart disease. We generated a human induced pluripotent stem cell (iPSC)-derived cardiomyocyte-specific cell cycle indicator system (TNNT2-FUCCI) to characterize regular and aberrant cardiomyocyte cycle dynamics. We visualized cell cycle progression in TNNT2-FUCCI and found G2 cycle arrest in endoreplicating cardiomyocytes. Moreover, we devised a live-cell compound screening platform to identify pro-proliferative drug candidates. We found that the alpha-adrenergic receptor agonist clonidine induced cardiomyocyte proliferation in vitro and increased cardiomyocyte cell cycle entry in neonatal mice. In conclusion, the TNNT2-FUCCI system is a versatile tool to characterize cardiomyocyte cell cycle dynamics and identify pro-proliferative candidates with regenerative potential in the mammalian heart.

Capsaicin Attenuates Arterial Calcification Through Promoting SIRT6-Mediated Deacetylation and Degradation of Hif1α (Hypoxic-Inducible Factor-1 Alpha)

BACKGROUND

Sustained Hif1α (hypoxic-inducible factor-1 alpha) accumulation plays a central role in osteogenic transdifferentiation and subsequent calcification. Capsaicin, the potent agonist of TRPV1 (transient receptor potential vanilloid type 1), was found to mitigate hypoxic-related injury and reverse phenotypic switch of vascular smooth muscle cells. However, its role in arterial calcification and the underlying mechanisms remain unexplored.

METHODS

We used data from Multi-Ethnic Study of Atherosclerosis to examine the association of coronary artery calcification and chili consumption. Chronic kidney disease mice and high phosphate-induced vascular smooth muscle cells calcification models were established to investigate the anticalcification effect of capsaicin, evaluated by calcium deposition and changes in phenotype markers.

RESULTS

Chili consumption was negatively correlated with coronary artery calcification and conferred a smaller progression burden during follow-up. Capsaicin reduced calcium deposition and osteogenic transdifferentiation both in vivo and in vitro. Using siTRPV1 and capsazepine, the anticalcification effect of capsaicin was abrogated. Hif1α was increased in Pi-treated vascular smooth muscle cells and its degradation was accelerated by capsaicin. Retaining Hif1α stability using CoCl2 or MG132 abolished the protective effect of capsaicin. We further identified an increased expression of SIRT6 in response to capsaicin and confirmed the physical interaction between SIRT6 and Hif1α. Acetylated Hif1α was decreased, whereas hydroxylated Hif1α was increased under capsaicin treatment. Using immunohistochemistry analysis, we observed increased SIRT6 and reduced Hif1α in both SIRT6 transgenic and capsaicin-treated chronic kidney disease mice.

CONCLUSIONS

Capsaicin facilitates deacetylation and degradation of Hif1α by upregulating SIRT6, which inhibits osteogenic transdifferentiation and protects against arterial calcification. These data highlight a promising therapeutic target for the management of arterial calcification.

6-Gingerol protects against cerebral ischemia/reperfusion injury by inhibiting NLRP3 inflammasome and apoptosis via TRPV1 / FAF1 complex dissociation-mediated autophagy

BACKGROUND

Our previous studies demonstrated that autophagy alleviates cerebral I/R injury by inhibiting NLRP3 inflammasome-mediated inflammation. 6-Gingerol, a phenolic compound extracted from ginger, was reported to possess potent antiapoptotic and anti-inflammatory activities and is associated with autophagy. However, the effects of 6-Gingerol in cerebral I/R injury have not been elucidated, and whether they involve autophagy-induced NLRP3 inflammasome inhibition remains unclear.

METHODS

Adult male Sprague-Dawley (SD) rats were subjected to middle cerebral artery occlusion (MCAO) for 1 h, followed by reperfusion for 24 h. 6-Gingerol and 3-methyladenine (3-MA) were injected intraperitoneally, and si-TRPV1 was injected via the lateral ventricle. Cerebral infarct volume, brain edema, neurological deficits, HE and Nissl were used to evaluate the morphological and functional changes of brain tissue, respectively. TRPV1, FAF1, autophagy related (LC3II/I, P62, Beclin1), inflammation related (NLRP3, cleaved-caspase-1, caspase-1, cleaved-IL-1β, IL-1β, cleaved-IL-18, IL-18) and apoptosis related (Bcl-2, Bax, cleaved-caspase-3) proteins were assessed by Western blot, immunofluorescence staining and coimmunoprecipitation, respectively. Enzyme linked immunosorbent assay (ELISA) was used to evaluate the changes in the expression levels of interleukin-1 (IL-1β) and interleukin-18(IL-18), respectively. The degree of neuronal apoptosis was evaluated by TUNEL staining. Neuronal ultrastructure was examined by transmission electron microscopy.

RESULT

6-Gingerol treatment significantly reduced cerebral infarct volume, improved brain edema and neurological scores, and reversed brain histomorphological damage after I/R injury. In addition, 6-Gingerol significantly reduced NLRP3 inflammasome-derived inflammation and neuronal apoptosis and upregulated autophagy. The autophagy inhibitor 3-MA rescued the effects of 6-Gingerol on the NLRP3 inflammasome and apoptosis. Moreover, the findings illustrated that 6-Gingerol inhibited autophagy-induced NLRP3 inflammasome activation and apoptosis through the dissociation of TRPV1 from FAF1.

CONCLUSION

In brief, 6-Gingerol exerts antiapoptotic and anti-inflammatory effects via TRPV1/FAF1 complex dissociation-mediated autophagy during cerebral I/R injury. Therefore, 6-Gingerol may be an effective drug for the treatment of I/R injury.

Calcium Signaling Regulates Autophagy and Apoptosis

Calcium (Ca²⁺) functions as a second messenger that is critical in regulating fundamental physiological functions such as cell growth/development, cell survival, neuronal development and/or the maintenance of cellular functions. The coordination among various proteins/pumps/Ca²⁺ channels and Ca²⁺ storage in various organelles is critical in maintaining cytosolic Ca²⁺ levels that provide the spatial resolution needed for cellular homeostasis. An important regulatory aspect of Ca²⁺ homeostasis is a store operated Ca²⁺ entry (SOCE) mechanism that is activated by the depletion of Ca²⁺ from internal ER stores and has gained much attention for influencing functions in both excitable and non-excitable cells. Ca²⁺ has been shown to regulate opposing functions such as autophagy, that promote cell survival; on the other hand, Ca²⁺ also regulates programmed cell death processes such as apoptosis. The functional significance of the TRP/Orai channels has been elaborately studied; however, information on how they can modulate opposing functions and modulate function in excitable and non-excitable cells is limited. Importantly, perturbations in SOCE have been implicated in a spectrum of pathological neurodegenerative conditions. The critical role of autophagy machinery in the pathogenesis of neurodegenerative diseases such as Alzheimer’s, Parkinson’s, and Huntington’s diseases, would presumably unveil avenues for plausible therapeutic interventions for these diseases. We thus review the role of SOCE-regulated Ca²⁺ signaling in modulating these diverse functions in stem cell, immune regulation and neuromodulation.

TRPV1 activation and internalization is part of the LPS-induced inflammation in human iPSC-derived cardiomyocytes

The non-selective cation channel transient receptor potential vanilloid 1 (TRPV1) is expressed throughout the cardiovascular system. Recent evidence shows a role for TRPV1 in inflammatory processes. The role of TRPV1 for myocardial inflammation has not been established yet. Human induced pluripotent stem cell (iPSC)-derived cardiomyocytes (hiPSC-CM) from 4 healthy donors were incubated with lipopolysaccharides (LPS, 6 h), TRPV1 agonist capsaicin (CAP, 20 min) or the antagonist capsazepine (CPZ, 20 min). TRPV1 expression was studied by PCR and western blotting. TRPV1 internalization was analyzed by immunofluorescence. Interleukin-6 (IL-6) secretion and phosphorylation of JNK, p38 and ERK were determined by ELISA. TRPV1-associated ion channel current was measured by patch clamp. TRPV1-mRNA and -protein were expressed in hiPSC-CM. TRPV1 was localized in the plasma membrane. LPS significantly increased secretion of IL-6 by 2.3-fold, which was prevented by pre-incubation with CPZ. LPS induced TRPV1 internalization. Phosphorylation levels of ERK, p38 or JNK were not altered by TRPV1 stimulation or inhibition. LPS and IL-6 significantly lowered TRPV1-mediated ion channel current. TRPV1 mediates the LPS-induced inflammation in cardiomyocytes, associated with changes of cellular electrophysiology. LPS-induced inflammation results in TRPV1 internalization. Further studies have to examine the underlying pathways and the clinical relevance of these findings.