Inflammation-induced TRPV4 channels exacerbate blood-brain barrier dysfunction in multiple sclerosis.

BACKGROUND: Blood-brain barrier (BBB) dysfunction and immune cell migration into the central nervous system (CNS) are pathogenic drivers of multiple sclerosis (MS). Ways to reinstate BBB function and subsequently limit neuroinflammation present promising strategies to restrict disease progression. However, to date, the molecular players directing BBB impairment in MS remain poorly understood. One suggested candidate to impact BBB function is the transient receptor potential vanilloid-type 4 ion channel (TRPV4), but its specific role in MS pathogenesis remains unclear. Here, we investigated the role of TRPV4 in BBB dysfunction in MS. MAIN TEXT: In human post-mortem MS brain tissue, we observed a region-specific increase in endothelial TRPV4 expression around mixed active/inactive lesions, which coincided with perivascular microglia enrichment in the same area. Using in vitro models, we identified that microglia-derived tumor necrosis factor-α (TNFα) induced brain endothelial TRPV4 expression. Also, we found that TRPV4 levels influenced brain endothelial barrier formation via expression of the brain endothelial tight junction molecule claudin-5. In contrast, during an inflammatory insult, TRPV4 promoted a pathological endothelial molecular signature, as evidenced by enhanced expression of inflammatory mediators and cell adhesion molecules. Moreover, TRPV4 activity mediated T cell extravasation across the brain endothelium. CONCLUSION: Collectively, our findings suggest a novel role for endothelial TRPV4 in MS, in which enhanced expression contributes to MS pathogenesis by driving BBB dysfunction and immune cell migration.

Calcium-activated potassium channels as amplifiers of TRPV4-mediated pulmonary edema formation in male mice.

BACKGROUND: As a mechanosensitive cation channel and key regulator of vascular barrier function, endothelial transient receptor potential vanilloid-type 4 (TRPV4) contributes critically to ventilator-induced lung injury (VILI) and edema formation. Ca2+ influx via TRPV4 can activate Ca2+-activated K + (KCa) channels, categorized into small (SK1-3), intermediate (IK1), and big (BK) KCa, which may in turn amplify Ca2+ influx by increasing the electrochemical Ca2+ gradient and thus, promote lung injury. We therefore hypothesized that endothelial KCa channels may contribute to the progression of TRPV4-mediated VILI. METHODS: Male C57Bl/6J mice were ventilated for 2 h with low or high tidal volumes in the presence or absence of the non-selective KCa antagonists apamin, charybdotoxin, or the selective IK1 antagonist TRAM34. Lung injury was similarly assessed in overventilated, endothelial-specific TRPV4-deficient mice or TRAM34-treated C57Bl/6J mice challenged with intratracheal acid installation. Changes in endothelial Ca2+ concentration ([Ca2+]i) were monitored by real-time imaging in isolated-perfused lungs in response to airway pressure elevation or in human pulmonary microvascular endothelial cells (HPMECs) in response to TRPV4 activation with or without inhibition of KCa channels. Analogously, changes in intracellular potassium concentration ([K+]i) and membrane potential (Vm) were imaged in vitro. RESULTS: Endothelial TRPV4 deficiency or inhibition of KCa channels, and most prominently inhibition of IK1 by TRAM34 attenuated VILI as demonstrated by reduced lung edema, protein leak, and by quantitative lung histology. All KCa antagonists reduced the [Ca2+]i response to mechanical stimulation or direct TRPV4 activation in isolated lungs. TRAM34 and charybdotoxin, yet not apamin prevented TRPV4-induced K+ efflux and membrane hyperpolarization in HPMECs. TRAM34 also attenuated the TRPV4 agonist-induced Ca2+ influx in vitro and reduced acid-induced lung injury in vivo. CONCLUSIONS: KCa channels, specifically IK1, act as amplifiers of TRPV4-mediated Ca2+ influx and establish a detrimental feedback that promotes barrier failure and drives the progression of VILI.

Epidemiology of myasthenia gravis in the United States.

Introduction: Global studies of epidemiology of myasthenia gravis (MG) have pointed to increasing prevalence of this rare autoimmune disorder affecting the neuromuscular synapse; however, no new data for the USA were available for decades. We aimed to estimate the incidence rate and prevalence of MG in a large-scale insured US population. Methods: We conducted a population-based retrospective cohort study to estimate the annual incidence and prevalence of MG cases in the USA during 2017. Using a previously validated algorithm, we identified cases of MG in two Truven Health MarketScan databases, which during 2017 included a sample of approximately 20 million commercially insured and Medicare recipients, plus 10 million Medicaid recipients. We report crude incidence and prevalence and calculated age-and sex-standardized estimates for the USA based on the 2017 American Community Survey. We estimated the number of adult cases during 2021 by extrapolating from the stratified estimates to the population size from the 2021 American Community Survey. Results: From the US commercially/Medicare-insured cohort, we calculated an age-and sex-standardized incidence of 68.5 new cases per million person-years with an adjusted prevalence of 316.4 per million. Within the Medicaid-insured population, similar yet slightly lower numbers emerged: the adjusted incidence was 49.7 new cases per million person-years, and the adjusted prevalence rate was 203.7 cases per million. Given our results, we were able to estimate that there were approximately 82,715 US adults living with MG in 2021 (or an estimated 320.2 cases per million adults in the USA). We observed a strong effect of age and sex when stratifying the identified incidence rate and prevalence, with a pattern of female preponderance among the younger age brackets, a male preponderance for older cases in the commercially/Medicare-insured cohort, and the disease incidence and prevalence steadily increasing with age. Discussion: Our updated US population-based estimates of MG epidemiology demonstrate an increase in the previously reported incidence and prevalence from over 20 years ago, in keeping with developments in westernized, industrialized countries. Notable findings of steadily increasing prevalence with age, driven by robust increases in elderly males, prompts questions for basic-translational research, therapeutics, and public health.