Using region-specific injection of hyaluronic acid, we developed a mouse model of acute retinal detachment (RD) to investigate molecular mechanisms of photoreceptor cell death triggered by RD. We ...focused on the transient receptor potential vanilloid 4 (TRPV4) ion channel, which functions as a thermosensor, osmosensor, and/or mechanosensor. After RD, the number of apoptotic photoreceptors was reduced by ∼50% in TRPV4KO mice relative to wild-type mice, indicating the possible involvement of TRPV4 activation in RD-induced photoreceptor cell death. Furthermore, TRPV4 expressed in Müller glial cells can be activated by mechanical stimuli caused by RD-induced swelling of these cells, resulting in release of the cytokine MCP-1, which is reported as a mediator of Müller glia-derived strong mediator for RD-induced photoreceptor death. We also found that the TRPV4 activation by the Müller glial swelling was potentiated by body temperature. Together, our results suggest that RD adversely impacts photoreceptor viability via TRPV4-dependent cytokine release from Müller glial cells and that TRPV4 is part of a novel molecular pathway that could exacerbate the effects of hypoxia on photoreceptor survival after RD.
Identification of the mechanisms of photoreceptor death in retinal detachment is required for establishment of therapeutic targets for preventing loss of visual acuity. In this study, we found that TRPV4 expressed in Müller glial cells can be activated by mechanical stimuli caused by RD-induced swelling of these cells, resulting in release of the cytokine MCP-1, which is reported as a mediator of Müller glia-derived strong mediator for RD-induced photoreceptor death. We also found that the TRPV4 activation by the Müller glial swelling was potentiated by body temperature. Hence, TRPV4 inhibition could suppress cell death in RD pathological conditions and suggests that TRPV4 in Müller glial cells might be a novel therapeutic target for preventing photoreceptor cell death after RD.
Group I metabotropic glutamate receptors, in particular mGluR5, have been implicated in various forms of synaptic plasticity that are believed to underlie declarative memory. We observed that mGluR5 ...specifically activated a channel containing TRPC1, an isoform of the canonical family of transient receptor potential (TRPC) channels highly expressed in CA1-3 regions of the hippocampus. TRPC1 is able to form tetrameric complexes with TRPC4 and/or TRPC5 isoforms. TRPC1/4/5 complexes have recently been involved in the efficiency of synaptic transmission in the hippocampus. We therefore used a mouse model devoid of TRPC1 expression to investigate the involvement of mGluR5-TRPC1 pathway in synaptic plasticity and memory formation.
mice showed alterations in spatial working memory and fear conditioning. Activation of mGluR increased synaptic excitability in neurons from WT but not from
mice. LTP triggered by a theta burst could not maintain over time in brain slices from
mice. mGluR-induced LTD was also impaired in these mice. Finally, acute inhibition of TRPC1 by Pico145 on isolated neurons or on brain slices mimicked the genetic depletion of
and inhibited mGluR-induced entry of cations and subsequent effects on synaptic plasticity, excluding developmental or compensatory mechanisms in
mice. In summary, our results indicate that TRPC1 plays a role in synaptic plasticity and spatial working memory processes.
Key points
Increase in blood pressure in the renal afferent arteriole is known to induce an increase in cytosolic calcium concentration (Ca2+i) of juxtaglomerular (JG) cells and to result in a ...decreased secretion of renin.
Mechanical stimulation of As4.1 JG cells induces an increase in Ca2+i that is inhibited by HC067047 and RN1734, two inhibitors of TRPV4, or by siRNA‐mediated repression of TRPV4.
Inhibition of TRPV4 impairs pressure‐induced decrease in renin secretion.
Compared to wild‐type mice, Trpv4−/− mice present increased resting plasma levels of renin and aldosterone and present a significantly altered pressure–renin relationship.
We suggest that TRPV4 channel participates in mechanosensation at the juxtaglomerular apparatus.
The renin–angiotensin system is a crucial blood pressure regulation system. It consists of a hormonal cascade where the rate‐limiting enzyme is renin, which is secreted into the blood flow by renal juxtaglomerular (JG) cells in response to low pressure in the renal afferent arteriole. In contrast, an increase in blood pressure results in a decreased renin secretion. This is accompanied by a transitory increase in Ca2+i of JG cells. The inverse relationship between Ca2+i and renin secretion has been called the ‘calcium paradox’ of renin release. How increased pressure induces a Ca2+i transient in JG cells, is however, unknown. We observed that Ca2+i transients induced by mechanical stimuli in JG As4.1 cells were completely abolished by HC067047 and RN1734, two inhibitors of TRPV4. They were also reduced by half by siRNA‐mediated repression of TRPV4 but not after repression or inhibition of TRPV2 or Piezo1 ion channels. Interestingly, the stimulation of renin secretion by the adenylate cyclase activator forskolin was totally inhibited by cyclic stretching of the cells. This effect was mimicked by stimulation with GSK1016790A and 4αPDD, two activators of TRPV4 and inhibited in the presence of HC067047. Moreover, in isolated perfused kidneys from Trpv4−/− mice, the pressure–renin relationship was significantly altered. In vivo, Trpv4−/− mice presented increased plasma levels of renin and aldosterone compared to wild‐type mice. Altogether, our results suggest that TRPV4 is involved in the pressure‐induced entry of Ca2+ in JG cells, which inhibits renin release and allows the negative feedback regulation on blood pressure.
Key points
Increase in blood pressure in the renal afferent arteriole is known to induce an increase in cytosolic calcium concentration (Ca2+i) of juxtaglomerular (JG) cells and to result in a decreased secretion of renin.
Mechanical stimulation of As4.1 JG cells induces an increase in Ca2+i that is inhibited by HC067047 and RN1734, two inhibitors of TRPV4, or by siRNA‐mediated repression of TRPV4.
Inhibition of TRPV4 impairs pressure‐induced decrease in renin secretion.
Compared to wild‐type mice, Trpv4−/− mice present increased resting plasma levels of renin and aldosterone and present a significantly altered pressure–renin relationship.
We suggest that TRPV4 channel participates in mechanosensation at the juxtaglomerular apparatus.
TRPV4 is a polymodal cation channel expressed in osmosensitive neurons of the hypothalamus and in the mammalian nephron. The segmental distribution and role(s) of TRPV4 in osmoregulation remain ...debated. We investigated the renal distribution pattern of TRPV4 and the functional consequences of its disruption in mouse models. Using qPCR on microdissected segments, immunohistochemistry, and a
LacZ
reporter mouse, we found that TRPV4 is abundantly expressed in the proximal tubule, the late distal convoluted tubule, and throughout the connecting tubule and collecting duct, including principal and intercalated cells. TRPV4 was undetectable in the glomeruli and thick ascending limb and weakly abundant in the early distal convoluted tubule. Metabolic studies in
Trpv4
+/+
and
Trpv4
−/−
littermates revealed that the lack of TRPV4 did not influence activity, food and water intake, renal function, and urinary concentration at baseline. The mice showed a similar response to furosemide, water loading and deprivation, acid loading, and dietary NaCl restriction. However,
Trpv4
−/−
mice showed a significantly lower vasopressin synthesis and release after water deprivation, with a loss of the positive correlation between plasma osmolality and plasma vasopressin levels, and a delayed water intake upon acute administration of hypertonic saline. Specific activation of TRPV4 in primary cultures of proximal tubule cells increased albumin uptake, whereas no effect of TRPV4 deletion could be observed at baseline. These data reveal that, despite its abundant expression in tubular segments, TRPV4 does not play a major role in the kidney or is efficiently compensated when deleted. Instead, TRPV4 is critical for the release of vasopressin, the sensation of thirst, and the central osmoregulation.
In‐center maintenance hemodialysis (HD) patients are at high risk of acquiring coronavirus disease 2019 (COVID‐19) by cross‐contamination inside the unit. The aim of this study was to assess ...retrospectively the dynamics of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) transmission during the very first pandemic phase (March–July 2020) in a cohort of in‐center maintenance HD patients and in nurses the same HD facility, using a phylogenetic approach. All SARS‐CoV‐2 quantitative reverse‐transcription polymerase chain reaction positive patients and nurses from our HD unit‐respectively 10 out of 98, and 8 out of 58‐ and two other positive patients dialyzed in our self‐care unit were included. Whole‐genome viral sequencing and phylogenetic analysis supported the cluster investigation. Five positive patients were usually dialyzed in the same room and same shift before their COVID‐19 diagnosis was made. Viral sequencing performed on 4/5 patients' swabs showed no phylogenetic link between their viruses. The fifth patient (whose virus could not be sequenced) was dialyzed at the end of the dialysis room and was treated by a different nurse than the one in charge of the other patients. Three nurses shared the same virus detected in both self‐care patients (one of them had been transferred to our in‐center facility). The epidemiologically strongly suspected intra‐unit cluster could be ruled out by viral genome sequencing. The infection control policy did not allow inter‐patient contamination within the HD facility, in contrast to evidence of moderate dissemination within the nursing staff and in the satellite unit. Epidemiologic data without phylogenetic confirmation might mislead the interpretation of the dynamics of viral spreading within congregate settings.
Highlights
In‐center maintenance hemodialysis (HD) patients are at high risk of acquiring coronavirus disease 2019 by cross‐contamination inside the unit. In this study we assessed the dynamics of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) transmission in a cohort of in‐center maintenance hemodialysis patients and in nurses the same HD facility in Brussels, Belgium, using whole‐genome viral sequencing and phylogenetic analysis.
All SARS‐CoV‐2 quantitative reverse‐transcription polymerase chain reaction (RT‐qPCR) positive patients (10 out 98) and nurses from our HD unit (8 out 58) and two other positive patients dialyzed in our self‐care unit were included. An intra‐unit cluster was suspected because five SARS‐CoV‐2 RT‐qPCR positive patients were dialyzed in the same room at the same time three times weekly.
The epidemiologically strongly suspected intra‐unit cluster could be ruled out by viral genome sequencing. In contrast, three nurses shared the same virus detected in both self‐care patients (one of them had been transferred to our in‐center facility).
Epidemiologic data without phylogenetic confirmation might mislead the interpretation of the dynamics of viral spreading within congregate settings.
Key points
Increased plasma osmolarity induces intracellular water depletion and cell shrinkage (CS) followed by activation of a regulatory volume increase (RVI).
In skeletal muscle, the hyperosmotic ...shock‐induced CS is accompanied by a small membrane depolarization responsible for a release of Ca2+ from intracellular pools.
Hyperosmotic shock also induces phosphorylation of STE20/SPS1‐related proline/alanine‐rich kinase (SPAK).
TRPV2 dominant negative expressing fibres challenged with hyperosmotic shock present a slower membrane depolarization, a diminished Ca2+ response, a smaller RVI response, a decrease in SPAK phosphorylation and defective muscle function.
We suggest that hyperosmotic shock induces TRPV2 activation, which accelerates muscle cell depolarization and allows the subsequent Ca2+ release from the sarcoplasmic reticulum, activation of the Na+–K+–Cl− cotransporter by SPAK, and the RVI response.
Increased plasma osmolarity induces intracellular water depletion and cell shrinkage followed by activation of a regulatory volume increase (RVI). In skeletal muscle, this is accompanied by transverse tubule (TT) dilatation and by a membrane depolarization responsible for a release of Ca2+ from intracellular pools. We observed that both hyperosmotic shock‐induced Ca2+ transients and RVI were inhibited by Gd3+, ruthenium red and GsMTx4 toxin, three inhibitors of mechanosensitive ion channels. The response was also completely absent in muscle fibres overexpressing a non‐permeant, dominant negative (DN) mutant of the transient receptor potential, V2 isoform (TRPV2) ion channel, suggesting the involvement of TRPV2 or of a TRP isoform susceptible to heterotetramerization with TRPV2. The release of Ca2+ induced by hyperosmotic shock was increased by cannabidiol, an activator of TRPV2, and decreased by tranilast, an inhibitor of TRPV2, suggesting a role for the TRPV2 channel itself. Hyperosmotic shock‐induced membrane depolarization was impaired in TRPV2‐DN fibres, suggesting that TRPV2 activation triggers the release of Ca2+ from the sarcoplasmic reticulum by depolarizing TTs. RVI requires the sequential activation of STE20/SPS1‐related proline/alanine‐rich kinase (SPAK) and NKCC1, a Na+–K+–Cl− cotransporter, allowing ion entry and driving osmotic water flow. In fibres overexpressing TRPV2‐DN as well as in fibres in which Ca2+ transients were abolished by the Ca2+ chelator BAPTA, the level of P‐SPAKSer373 in response to hyperosmotic shock was reduced, suggesting a modulation of SPAK phosphorylation by intracellular Ca2+. We conclude that TRPV2 is involved in osmosensation in skeletal muscle fibres, acting in concert with P‐SPAK‐activated NKCC1.
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