TRPV4 regulates mitochondrial Ca2+-status and physiology in primary murine T cells based on their immunological state

Metal-modulated T cell antitumor immunity and emerging metalloimmunotherapy

In recent years, increasing evidence has shown that metals play important roles in both innate and adaptive immunity. An emerging concept of metalloimmunotherapy has been proposed, which may accelerate the development of immunotherapy for cancers. Here, we discuss how metals affect T cell function through different signaling pathways. Metals impact the fate of T cells, including their activation, proliferation, cytotoxicity, and differentiation. Most importantly, metals also participate in mitochondrial operation by regulating energy production and reactive oxygen species homeostasis in T cells. We also identified the metal-based mutual effects between tumor cells and T cells in the tumor microenvironment. Overall, the antitumor effect of T cells can be improved by targeting metal metabolism and metalloimmunotherapy, which will be a step forward in the treatment of cancers.

Emerging roles of mechanically activated ion channels in autoimmune disease

Mechanically activated (MA) ion channels have rapidly gained prominence as vital conduits bridging aberrant mechanical cues in tissues with the dysregulated immune responses at the core of autoimmune diseases. Once regarded as peripheral players in inflammation, these channels, exemplified by PIEZO1, TRPV4, and specific K2P family members, now play a central role in modulating T-cell effector functions, B- cell activation and the activity of macrophages and dendritic cells. Their gating is intimately tied to physical distortions such as increased tissue stiffness, osmotic imbalances, or fluid shear, triggering a cascade of ionic fluxes that elevate proinflammatory signaling and drive tissue-destructive loops. Recognition of these channels as central mediators of mechanical stress-induced inflammation responses in autoimmune pathogenesis is rapidly expanding. In parallel, the emerging therapeutic strategies aim to restrain overactive mechanosensors or selectively harness them in affected tissues. Small molecules, peptide blockers, and gene-targeting approaches show preclinical promise, although off-target effects and the broader homeostatic roles of these channels warrant caution. This review explores how integrating mechanobiological concepts with established immunological paradigms enables a more detailed understanding of autoimmune pathogenesis. By elucidating how mechanical forces potentiate or dampen pathological immunity, we propose innovative strategies that exploit mechanosensitivity to recalibrate immune responses across a spectrum of autoimmune conditions.

Conserved and Unique Mitochondrial Target Sequence of TRPV4 Can Independently Regulate Mitochondrial Functions

Though mitochondria have their own genome and protein synthesis machineries, the majority of the mitochondrial proteins are actually encoded by the nuclear genome. Most of these mitochondrial proteins are imported into specific compartments of the mitochondria due to their mitochondrial target sequence (MTS). Unlike the nuclear target sequence, the MTS of most of the mitochondrial localized proteins remain poorly understood, mainly due to their variability, heterogeneity, unconventional modes of action, mitochondrial potential-dependent transport, and other complexities. Recently, we reported that transient receptor potential vanilloid subtype 4 (TRPV4), a thermosensitive cation channel, is physically located at the mitochondria. Here we characterize a small segment (AA 592-630) located at the TM4-loop4-TM5 segment of TRPV4 that acts as a novel MTS. The same region remains highly conserved in all vertebrates and contains a large number of point mutations each of which causes an diverse spectrum of diseases in human. Using confocal and super-resolution microscopy, we show that this MTS of TRPV4 or its mutants localizes to the mitochondria independently and also induces functional and quantitative changes in the mitochondria. By using conformal microscopy, we could detect the presence of the MTS region within the isolated mitochondria. These findings may be important to understand the complexity of MTS and TRPV4-induced channelopathies better.

T cell-based cancer immunotherapy: opportunities and challenges

T cells play a central role in the cancer immunity cycle. The therapeutic outcomes of T cell-based intervention strategies are determined by multiple factors at various stages of the cycle. Here, we summarize and discuss recent advances in T cell immunotherapy and potential barriers to it within the framework of the cancer immunity cycle, including T-cell recognition of tumor antigens for activation, T cell trafficking and infiltration into tumors, and killing of target cells. Moreover, we discuss the key factors influencing T cell differentiation and functionality, including TCR stimulation, costimulatory signals, cytokines, metabolic reprogramming, and mechanistic forces. We also highlight the key transcription factors dictating T cell differentiation and discuss how metabolic circuits and specific metabolites shape the epigenetic program of tumor-infiltrating T cells. We conclude that a better understanding of T cell fate decision will help design novel strategies to overcome the barriers to effective cancer immunity.

TRPV4 Channel in Neurological Disease: from Molecular Mechanisms to Therapeutic Potential

Transient Receptor Potential Vanilloid 4 (TRPV4) is a non-selective cation channel with pivotal roles in various physiological processes, including osmosensitivity, mechanosensation, neuronal development, vascular tone regulation, and bone homeostasis in human bodies. Recent studies have made significant progress in understanding the structure and functional role of TRPV4, shedding light on its involvement in pathological processes, particularly in the realm of neurological diseases. Here, we aim to provide a comprehensive exploration of the multifaceted contributions of TRPV4 to neurological diseases, spanning its intricate molecular mechanisms to its potential as a target for therapeutic interventions. We delve into the structural and functional attributes of TRPV4, scrutinize its expression profile, and elucidate the possible mechanisms through which it participates in the pathogenesis of neurological disorders. Furthermore, we discussed recent years' progress in therapeutic strategies aimed at harnessing TRPV4 for the treatment of these diseases. These insights will provide a basis for understanding and designing modality-specific pharmacological agents to treat TRPV4-associated disorders.

Advances in ligand-based surface engineering strategies for fine-tuning T cell mechanotransduction toward efficient immunotherapy

T cell-based immunotherapy has recently emerged as a promising strategy to treat cancer, requiring the activation of antigen-directed cytotoxicity to eliminate cancer cells. Mechanical signaling, although often overshadowed by its biochemical counterpart, plays a crucial role in T cell anticancer responses, from activation to cytolytic killing. Rapid advancements in the fields of chemistry, biomaterials, and micro/nanoengineering offer an interdisciplinary approach to incorporating mechano- and immunomodulatory ligands, including but not limited to synthetic peptides, small molecules, cytokines, and artificial antigens, onto the biomaterial-based platforms to modulate mechanotransducive processes in T cells. The surface engineering of these immunomodulatory ligands with optimization of ligand density, geometrical arrangement, and mobility has been proven to better mimic the natural ligation between immunoreceptors and ligands to directly enhance or inhibit mechanotransduction pathways in T cells, through triggering upstream mechanosensitive channels, adhesion molecules, cytoskeletal components, or downstream mechanoimmunological regulators. Despite its tremendous potential, current research on this new biomaterial surface engineering approach for mechanomodulatory T cell activation and effector functions remains in a nascent stage. This review highlights the recent progress in this new direction, focusing on achievements in mechanomodulatory ligand-based surface engineering strategies and underlying principles, and outlooks the further research in the rapidly evolving field of T cell mechanotransduction engineering for efficient immunotherapy.

TRPM8 affects relative "cooling and heating" of subcellular organelles in microglia in a context-dependent manner

Thermoregulation and thermal homeostasis at the cellular and subcellular organelle level are poorly understood events. In this work, we used BV2, a microglial cell line, and a series of thermo-sensitive subcellular organelle-specific probes to analyze the relative changes in the spatio-temporal temperatures of different subcellular organelles, both qualitatively and quantitatively. These methodologies allowed us to understand the thermal relationship of different subcellular organelles also. We modulated BV2 cells by pharmacological application of activator or inhibitor of TRPM8 ion channel (a cold-sensitive ion channel) and/or by treating the cells with LPS, a molecule that induces pathogen-associated molecular patterns (PAMPs) signaling. We demonstrate that the temperatures of individual organelles remain variable within a physiological range, yet vary in different conditions. We also demonstrate that treating BV2 cells by TRPM8 modulators and/or LPS alters the organelle temperatures in a specific and context-dependent manner. We show that TRPM8 modulation and/or LPS can alter the relationship of mitochondrial membrane potential to mitochondrial temperature. Our work suggests that mitochondrial temperature positively influences ER temperature and negatively influences Golgi temperature. Golgi temperature positively influences membrane temperature. This understanding of thermal relationships may be crucial for dissecting cellular structures, function, and stress signaling and may be relevant for different diseases.

TRPV4 mediates IL-1-induced Ca2+ signaling, ERK activation and MMP expression

Ca2+ permeation through TRPV4 in fibroblasts is associated with pathological matrix degradation. In human gingival fibroblasts, IL-1β binding to its signaling receptor (IL-1R1) induces activation of extracellular regulated kinase (ERK) and MMP1 expression, processes that require Ca2+ flux across the plasma membrane. It is not known how IL-1R1, which does not conduct Ca2+, generates Ca2+ signals in response to IL-1. We examined whether TRPV4 mediates the Ca2+ fluxes required for ERK signaling in IL-1 stimulated gingival fibroblasts. TRPV4 was immunostained in fibroblasts of human gingival connective tissue and in focal adhesions of cultured mouse gingival fibroblasts. Human gingival fibroblasts treated with IL-1β showed no change of TRPV4 expression but there was increased MMP1 expression. In mouse, gingival fibroblasts expressing TRPV4, IL-1 strongly increased [Ca2+]i. Pre-incubation of cells with IL-1 Receptor Antagonist blocked Ca2+ entry induced by IL-1 or the TRPV4 agonist GSK101. Knockout of TRPV4 or expression of a non-Ca2+-conducting TRPV4 pore-mutant or pre-incubation with the TRPV4 inhibitor RN1734, blocked IL-1-induced Ca2+ transients and expression of the mouse interstitial collagenase, MMP13. Treatment of mouse gingival fibroblasts with GSK101 phenocopied Ca2+ and ERK responses induced by IL-1; these responses were absent in TRPV4-null cells or cells expressing a non-conducting TRPV4 pore-mutant. Immunostained IL-1R1 localized with TRPV4 in adhesions within cell extensions. While TRPV4 immunoprecipitates analyzed by mass spectrometry showed no association with IL-1R1, TRPV4 associated with Src-related proteins and Src co-immunoprecipitated with TRPV4. Src inhibition reduced IL-1-induced Ca2+ responses. The functional linkage of TRPV4 with IL-1R1 expands its repertoire of innate immune signaling processes by mediating IL-1-driven Ca2+ responses that drive matrix remodeling in fibroblasts. Thus, inhibiting TRPV4 activity may provide a new pharmacological approach for blunting matrix degradation in inflammatory diseases.

TRPV4 Activator-Containing CMT-Hy Hydrogel Enhances Bone Tissue Regeneration In Vivo by Enhancing Mitochondrial Health

Treating different types of bone defects is difficult, complicated, time-consuming, and expensive. Here, we demonstrate that transient receptor potential cation channel subfamily V member 4 (TRPV4), a mechanosensitive, thermogated, and nonselective cation channel, is endogenously present in the mesenchymal stem cells (MSCs). TRPV4 regulates both cytosolic Ca2+ levels and mitochondrial health. Accordingly, the hydrogel made from a natural modified biopolymer carboxymethyl tamarind CMT-Hy and encapsulated with TRPV4-modulatory agents affects different parameters of MSCs, such as cell morphology, focal adhesion points, intracellular Ca2+, and reactive oxygen species- and NO-levels. TRPV4 also regulates cell differentiation and biomineralization in vitro. We demonstrate that 4α-10-CMT-Hy and 4α-50-CMT-Hy (the hydrogel encapsulated with 4αPDD, 10 and 50 nM, TRPV4 activator) surfaces upregulate mitochondrial health, i.e., an increase in ATP- and cardiolipin-levels, and improve the mitochondrial membrane potential. The same scaffold turned out to be nontoxic in vivo. 4α-50-CMT-Hy enhances the repair of the bone-drill hole in rat femur, both qualitatively and quantitatively in vivo. We conclude that 4α-50-CMT-Hy as a scaffold is suitable for treating large-scale bone defects at low cost and can be tested for clinical trials.

TRP Ion Channels in Immune Cells and Their Implications for Inflammation

The transient receptor potential (TRP) ion channels act as cellular sensors and mediate a plethora of physiological processes, including somatosensation, proliferation, apoptosis, and metabolism. Under specific conditions, certain TRP channels are involved in inflammation and immune responses. Thus, focusing on the role of TRPs in immune system cells may contribute to resolving inflammation. In this review, we discuss the distribution of five subfamilies of mammalian TRP ion channels in immune system cells and how these ion channels function in inflammatory mechanisms. This review provides an overview of the current understanding of TRP ion channels in mediating inflammation and may offer potential avenues for therapeutic intervention.

Menthol causes mitochondrial Ca2+-influx, affects structure-function relationship and cools mitochondria

Menthol is a small bioactive compound able to cause several physiological changes and has multiple molecular targets. Therefore, cellular response against menthol is complex, and still poorly understood. In this work, we used a human osteosarcoma cell line (Saos-2) and analysed the effect of menthol, especially in terms of cellular, subcellular and molecular aspects. We demonstrate that menthol causes increased mitochondrial Ca2+ in a complex manner, which is mainly contributed by intracellular sources, including ER. Menthol also changes the Ca2+-load of individual mitochondrial particles in different conditions. Menthol increases ER-mito contact points, causes mitochondrial morphological changes, and increases mitochondrial ATP, cardiolipin, mitochondrial ROS and reduces mitochondrial membrane potential (ΔΨm). Menthol also prevents the mitochondrial quality damaged by sub-lethal and lethal doses of CCCP. In addition, menthol lowers the mitochondrial temperature within cell and also serves as a cooling agent for the isolated mitochondria in a cell free system too. Notably, menthol-induced reduction of mitochondrial temperature is observed in diverse types of cells, including neuronal, immune and cancer cells. As the higher mitochondrial temperature is a hallmark of several inflammatory, metabolic, disease and age-related disorders, we propose that menthol can serve as an active anti-aging compound against all these disorders. These findings may have relevance in case of several pharmacological and clinical applications of menthol. SIGNIFICANCE STATEMENT: Menthol is a plant-derived bioactive compound that is widely used for several physiological, behavioural, addictive, and medicinal purposes. It is a well-established "cooling and analgesic agent". However, the exact cellular and sub-cellular responses of menthol is poorly understood. In this work, we have characterized the effects of menthol on mitochondrial metabolism. Menthol regulates mitochondrial Ca2+, ATP, superoxides, cardiolipin, membrane-potential, and ER-mito contact sites. Moreover, the cooling agent menthol also cools down mitochondria and protects mitochondrial damage by certain toxins. These findings may promote use of menthol as a useful supplementary agent for anti-aging, anti-cancer, anti-inflammatory purposes where higher mitochondrial temperature is prevalent.

TRPV4 regulates osteoblast differentiation and mitochondrial function that are relevant for channelopathy

Different ion channels present in the osteoblast regulate the cellular functions including bio-mineralization, a process that is a highly stochastic event. Cellular events and molecular signaling involved in such process is poorly understood. Here we demonstrate that TRPV4, a mechanosensitive ion channel is endogenously present in an osteoblast cell line (MC3T3-E1) and in primary osteoblasts. Pharmacological activation of TRPV4 enhanced intracellular Ca²⁺-level, expression of osteoblast-specific genes and caused increased bio-mineralization. TRPV4 activation also affects mitochondrial Ca²⁺-levels and mitochondrial metabolisms. We further demonstrate that different point mutants of TRPV4 induce different mitochondrial morphology and have different levels of mitochondrial translocation, collectively suggesting that TRPV4-mutation-induced bone disorders and other channelopathies are mostly due to mitochondrial abnormalities. These findings may have broad biomedical implications.