TRPV4 acts as a mitochondrial Ca2+-importer and regulates mitochondrial temperature and metabolism

Taxol-treatment alters endogenous TRPV1 expression and mitochondrial membrane potential in mesenchymal stem cells: Relevant in chemotherapy-induced pathophysiology

Microtubule-based chemotherapeutics, primarily Taxane-derived agents are still used as the major live-saving agents, yet have several side effects including serious loss of immune cells, bone density etc. which lowers the quality of life. This imposes the need to understand the effects of these agents on Mesenchymal Stem Cells (MSCs) in details. In this work we demonstrate that Taxol and Nocodazole affects the endogenous expression of TRPV1, a non-selective cation channel in MSCs. These agents also affect the status of polymerized Actin as well as Tyrosinated-tubulin, basal cytosolic Ca2+ and mitochondrial membrane potential (ΔΨm). Notably, pharmacological modulation of TRPV1 by Capsaicin or Capsazepine can also alter the above-mentioned parameters in a context-dependent manner. We suggest that endogenous expression of TRPV1 and pharmacological modulation of TRPV1 can be utilized to rescue some of these parameters effectively. These findings may have significance in the treatments and strategies with Microtubule-based chemotherapeutics and stem-cell based therapy.

TRPV4 modulation affects mitochondrial parameters in adipocytes and its inhibition upregulates lipid accumulation

Enhanced lipid-droplet formation by adipocytes is a complex process and relevant for obesity. Using knock-out animals, involvement of TRPV4, a thermosensitive ion channel in the obesity has been proposed. However, exact role/s of TRPV4 in adipogenesis and obesity remain unclear and contradictory. Here we used in vitro culture of 3T3L-1 preadipocytes and primary murine-mesenchymal stem cells as model systems, and a series of live-cell-imaging to analyse the direct involvement of TRPV4 exclusively at the adipocytes that are free from other complex signalling as expected in in-vivo condition. Functional TRPV4 is endogenously expressed in pre- and in mature-adipocytes. Pharmacological inhibition of TRPV4 enhances differentiation of preadipocytes to mature adipocytes, increases expression of adipogenic and lipogenic genes, enhances cholesterol, promotes bigger lipid-droplet formation and reduces the lipid droplet temperature. On the other hand, TRPV4 activation enhanced the browning of adipocytes with increased UCP-1 levels. TRPV4 regulates mitochondrial-temperature, Ca2+-load, ATP, superoxides, cardiolipin, membrane potential (ΔΨm), and lipid-mitochondrial contact sites. TRPV4 also regulates the extent of actin fibres, affecting the cells mechanosensing ability. These findings link TRPV4-mediated mitochondrial changes in the context of lipid-droplet formation involved in adipogenesis and confirm the direct involvement of TRPV4 in adipogenesis. These findings may have broad implication in treating adipogenesis and obesity in future.

Pharmacological agents targeting transient receptor potential (TRP) channels in neuropathic pain: Preclinical and clinical status

Neuropathic pain generally affects 7-10% population worldwide and an estimated ∼1 in every 20 individuals in western countries suffer and burden to society. The most limiting factor with existing therapies includes dose escalation issues, off-target side effects and poor translation of randomized trials into clinical practice. Neuropathic pain is a broad term that comprises direct injury/damage to the central and/or peripheral nervous system, leads to maladaptive changes in neuronal as well as in non-neuronal cells, which further contributes to the spontaneous pain, sensory and motor deficit along with altered sensitivity towards the noxious as well as non-noxious stimulus. Transient receptor potential (TRP) channels are polymodal, non-specific cation channels that operate as biosensors to various mechanical and chemical stimuli, including hyperosmolarity, shear stress, heat, mechanical stretch, extracellular ATP, and other products of inflammation. Modulation of these channels leads to various physiological and pathophysiological manifestations at molecular and cellular levels, leading to diseases including neuropathic pain. There are several molecules targeting TRP channels for neuropathic pain in pre-clinical studies, clinical trials and in the market. This review highlights the critical involvement of various pharmacological modulators for TRP channels targeting neuropathic pain and their possible outcomes to harness the therapeutic potential of TRP channels.

Clinical and Genetic Profiles of 5q- and Non-5q-Spinal Muscular Atrophy Diseases in Pediatric Patients

BACKGROUND

Spinal muscular atrophy (SMA) is a genetic disease characterized by loss of motor neurons in the spinal cord and lower brainstem. The term "SMA" usually refers to the most common form, 5q-SMA, which is caused by biallelic mutations in SMN1 (located on chromosome 5q13). However, long before the discovery of SMN1, it was known that other forms of SMA existed. Therefore, SMA is currently divided into two groups: 5q-SMA and non-5q-SMA. This is a simple and practical classification, and therapeutic drugs have only been developed for 5q-SMA (nusinersen, onasemnogene abeparvovec, risdiplam) and not for non-5q-SMA disease.

METHODS

We conducted a non-systematic critical review to identify the characteristics of each SMA disease.

RESULTS

Many of the non-5q-SMA diseases have similar symptoms, making DNA analysis of patients essential for accurate diagnosis. Currently, genetic analysis technology using next-generation sequencers is rapidly advancing, opening up the possibility of elucidating the pathology and treating non-5q-SMA.

CONCLUSION

Based on accurate diagnosis and a deeper understanding of the pathology of each disease, treatments for non-5q-SMA diseases may be developed in the near future.

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.

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 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.

TRPV4-mediated Ca2+ deregulation causes mitochondrial dysfunction via the AKT/α-synuclein pathway in dopaminergic neurons

Mutations in the gene encoding the transient receptor potential vanilloid member 4 (TRPV4), a Ca2+ permeable nonselective cation channel, cause TRPV4-related disorders. TRPV4 is widely expressed in the brain; however, the pathogenesis underlying TRPV4-mediated Ca2+ deregulation in neurodevelopment remains unresolved and an effective therapeutic strategy remains to be established. These issues were addressed by isolating mutant dental pulp stem cells from a tooth donated by a child diagnosed with metatropic dysplasia with neurodevelopmental comorbidities caused by a gain-of-function TRPV4 mutation, c.1855C > T (p.L619F). The mutation was repaired using CRISPR/Cas9 to generate corrected isogenic stem cells. These stem cells were differentiated into dopaminergic neurons and the pharmacological effects of folic acid were examined. In mutant neurons, constitutively elevated cytosolic Ca2+ augmented AKT-mediated α-synuclein (α-syn) induction, resulting in mitochondrial Ca2+ accumulation and dysfunction. The TRPV4 antagonist, AKT inhibitor, or α-syn knockdown, normalizes the mitochondrial Ca2+ levels in mutant neurons, suggesting the importance of mutant TRPV4/Ca2+/AKT-induced α-syn in mitochondrial Ca2+ accumulation. Folic acid was effective in normalizing mitochondrial Ca2+ levels via the transcriptional repression of α-syn and improving mitochondrial reactive oxygen species levels, adenosine triphosphate synthesis, and neurite outgrowth of mutant neurons. This study provides new insights into the neuropathological mechanisms underlying TRPV4-related disorders and related therapeutic strategies.

The Lysosomal Calcium Channel TRPML1 Maintains Mitochondrial Fitness in NK Cells through Interorganelle Cross-Talk

Cytotoxic lymphocytes eliminate cancer cells through the release of lytic granules, a specialized form of secretory lysosomes. This compartment is part of the pleomorphic endolysosomal system and is distinguished by its highly dynamic Ca2+ signaling machinery. Several transient receptor potential (TRP) calcium channels play essential roles in endolysosomal Ca2+ signaling and ensure the proper function of these organelles. In this study, we examined the role of TRPML1 (TRP cation channel, mucolipin subfamily, member 1) in regulating the homeostasis of secretory lysosomes and their cross-talk with mitochondria in human NK cells. We found that genetic deletion of TRPML1, which localizes to lysosomes in NK cells, led to mitochondrial fragmentation with evidence of collapsed mitochondrial cristae. Consequently, TRPML1-/- NK92 (NK92ML1-/-) displayed loss of mitochondrial membrane potential, increased reactive oxygen species stress, reduced ATP production, and compromised respiratory capacity. Using sensitive organelle-specific probes, we observed that mitochondria in NK92ML1-/- cells exhibited evidence of Ca2+ overload. Moreover, pharmacological activation of the TRPML1 channel in primary NK cells resulted in upregulation of LC3-II, whereas genetic deletion impeded autophagic flux and increased accumulation of dysfunctional mitochondria. Thus, TRPML1 impacts autophagy and clearance of damaged mitochondria. Taken together, these results suggest that an intimate interorganelle communication in NK cells is orchestrated by the lysosomal Ca2+ channel TRPML1.

Progesterone interacts with the mutational hot-spot of TRPV4 and acts as a ligand relevant for fast Ca2+-signalling

Steroids are also known to induce immediate physiological and cellular response which occurs within minutes to seconds, or even faster. Such non-genomic actions of steroids are rapid and are proposed to be mediated by different ion channels. Transient receptor potential vanilloid sub-type 4 (TRPV4), is a non-specific polymodal ion channel which is involved in several physiological and cellular processes. In this work, we explored the possibilities of Progesterone (P4) as an endogenous ligand for TRPV4. We demonstrate that P4 docks as well as physically interacts with the TM4-loop-TM5 region of TRPV4, a region which is a mutational hotspot for different diseases. Live cell imaging experiments with a genetically encoded Ca2+-sensor suggests that P4 causes quick influx of Ca2+ specifically in the TRPV4 expressing cells, which can be partially blocked by TRPV4-specific inhibitor, suggesting that P4 can act as a ligand for TRPV4. Such P4-mediated Ca2+-influx is altered in cells expressing disease causing TRPV4 mutants, namely in L596P, R616Q, and also in embryonic lethal mutant L618P. P4 dampens, both in terms of "extent" as well as the "pattern" of the Ca2+-influx by other stimulus too in cells expressing TRPV4-Wt, suggesting that P4 crosstalk with the TRPV4-mediated Ca2+-signalling, both in quick and long-term manner. We propose that P4 crosstalk with TRPV4 might be relevant for both acute and chronic pain as well as for other health-related functions.

A TRPV4 mutation caused Charcot-Marie-Tooth disease type 2C with scapuloperoneal muscular atrophy overlap syndrome and scapuloperoneal spinal muscular atrophy in one family: a case report and literature review

BACKGROUND

Charcot-Marie-Tooth disease 2C (CMT2C) and scapuloperoneal spinal muscular atrophy (SPSMA) are different clinical phenotypes of TRPV4 mutation. The mutation of p.R316C has been reported to cause CMT2C and SPSMA separately.

CASE PRESENTATION

Here, we reported a Chinese family harboring the same p.R316C variant, but with an overlap syndrome and different clinical manifestations. A 58-year-old man presented with severe scapula muscle atrophy, resulting in sloping shoulders. He also exhibited distinct muscle atrophy in his four limbs, particularly in the lower limbs. The sural nerve biopsy revealed severe loss of myelinated nerve fibers with scattered regenerating clusters and pseudo-onion bulbs. Nerve conduction study showed axon damage in both motor and sensory nerves. Sensory nerve action potentials could not be evoked in bilateral sural or superficial peroneal nerves. He was diagnosed with Charcot-Marie-Tooth disease type 2C and scapuloperoneal muscular atrophy overlap syndrome, whereas his 27-year-old son was born with clubfoot and clinodactyly. Electromyogram examination indicated chronic neurogenic changes and anterior horn cells involvement. Although there was no obvious weakness or sensory symptoms, early SPSMA could be considered for him.

CONCLUSIONS

A literature review of the clinical characteristics in CMT2C and SPSMA patients with TRPV4 mutation suggested that our case was distinct due to the overlap syndrome and phenotype variation. Altogether, this case broadened the phenotype spectrum and provided the nerve biopsy pathological details of TRPV4-related neuropathies.

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.

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

T cell activation process is critically affected by temperature and intracellular Ca²⁺-signalling. Yet, the nature and the key molecules involved in such complex Ca²⁺-signalling is poorly understood. It is mostly assumed that ion channels present in the plasma membrane primarily regulate the cytosolic Ca²⁺-levels exclusively. TRPV4 is a non-selective Ca²⁺ channel which can be activated at physiological temperature. TRPV4 is involved in several physiological, pathophysiological process as well as different forms of pain. Here we demonstrate that TRPV4 is endogenously expressed in T cell and is present in the mitochondria of T cells. TRPV4 activation increases mitochondrial Ca²⁺-levels, and alters mitochondrial temperature as well as specific metabolisms. The TRPV4-dependent increment in the mitochondrial Ca²⁺ is context-dependent and not just passively due to the increment in the cytosolic Ca²⁺. Our work also indicates that mitochondrial Ca²⁺-level correlates positively with a series of essential factors, such as mitochondrial membrane potential, mitochondrial ATP production and negatively correlates with certain factors such as mitochondrial temperature. We propose that TRPV4-mediated mitochondrial Ca²⁺-signalling and other metabolisms has implications in the immune activation process including immune synapse formation. Our data also endorse the re-evaluation of Ca²⁺-signalling in T cell, especially in the light of mitochondrial Ca²⁺-buffering and in higher body temperature, such as in case of fever. Presence of TRPV4 in the mitochondria of T cell is relevant for proper and optimum immune response and may provide evolutionary adaptive benefit. These findings may also have broad implications in different pathophysiological process, neuro-immune cross-talks, and channelopathies involving TRPV4.