Transient receptor potential ankyrin repeat 1 (TRPA1) forms calcium (Ca²⁺)- and zinc (Zn²⁺)-permeable ion channels that sense noxious substances. Despite the biological and clinical importance of TRPA1, there is little knowledge of the mechanisms that lead to transcriptional regulation of TRPA1 and of the functional role of transcriptionally induced TRPA1. Here we show induction of TRPA1 by inflammatory mediators and delineate the underlying molecular mechanisms and functional relevance. In human fibroblast-like synoviocytes, key inflammatory mediators (tumor necrosis factor-α and interleukin-1α) induced TRPA1 gene expression via nuclear factor-κB signaling and downstream activation of the transcription factor hypoxia-inducible factor-1α (HIF1α). HIF1α unexpectedly acted by binding to a specific hypoxia response element-like motif and its flanking regions in the TRPA1 gene. The induced TRPA1 channels, which were intrinsically activated by endogenous hydrogen peroxide and Zn²⁺, suppressed secretion of interleukin-6 and interleukin-8. The data suggest a previously unrecognized HIF1α mechanism that links inflammatory mediators to ion channel expression.

Mechanical-loading and unloading can modify osteoblast functioning. Ca²⁺ signaling is one of the earliest events in osteoblasts to induce a mechanical stimulus, thereby demonstrating the importance of the underlying mechanical sensors for the sensation. Here, we examined the mechano-sensitive channels PIEZO1 and TRPV4 were involved in the process of mechano-sensation in the osteoblastic MC3T3-E1 cells. The analysis of mRNA expression revealed a high expression of Piezo1 and Trpv4 in these cells. We also found that a PIEZO1 agonist, Yoda1, induced Ca²⁺ response and activated cationic currents in these cells. Ca²⁺ response was elicited when mechanical stimulation (MS), with shear stress, was induced by fluid flow in the MC3T3-E1 cells. Gene knockdown of Piezo1 in the MC3T3-E1 cells, by transfection with siPiezo1, inhibited the Yoda1-induced response, but failed to inhibit the MS-induced response. When MC3T3-E1 cells were transfected with siTrpv4, the MS-induced response was abolished and Yoda1 response was attenuated. Moreover, the MS-induced response was inhibited by a TRPV4 antagonist HC-067047 (HC). Yoda1 response was also inhibited by HC in MC3T3-E1 cells and HEK cells, expressing both PIEZO1 and TRPV4. Meanwhile, the activation of PIEZO1 and TRPV4 reduced the proliferation of MC3T3-E1, which was reversed by knockdown of PIEZO1, and TRPV4, respectively. In conclusion, TRPV4 and PIEZO1 are distinct mechano-sensors in the MC3T3-E1 cells. However, PIEZO1 and TRPV4 modify the proliferation of these cells, implying that PIEZO1 and TRPV4 may be functional in the osteoblastic mechano-transduction. Notably, it is also found that Yoda1 can induce TRPV4-dependent Ca²⁺ response, when both PIEZO1 and TRPV4 are highly expressed.

Proteins of the TRPC family can form many homo- and heterotetrameric cation channels permeable to Na⁺, K⁺ and Ca²⁺. In this review, we focus on channels formed by the isoforms TRPC1, TRPC4 and TRPC5. We review evidence for the formation of different TRPC1/4/5 tetramers, give an overview of recently developed small-molecule TRPC1/4/5 activators and inhibitors, highlight examples of biological roles of TRPC1/4/5 channels in different tissues and pathologies, and discuss how high-quality chemical probes of TRPC1/4/5 modulators can be used to understand the involvement of TRPC1/4/5 channels in physiological and pathophysiological processes.

Background and Purpose: The TRPC1, TRPC4, and TRPC5 proteins form homotetrameric or heterotetrameric, calcium‐permeable cation channels that are involved in various disease states. Recent research has yielded specific and potent xanthine‐based TRPC1/4/5 inhibitors. Here, we investigated the possibility of xanthine‐based activators of these channels.Experimental Approach: An analogue of the TRPC1/4/5 inhibitor Pico145, AM237, was synthesized and its activity was investigated using HEK cells overexpressing TRPC4, TRPC5, TRPC4–C1, TRPC5–C1, TRPC1:C4 or TRPC1:C5 channels, and in A498 cells expressing native TRPC1:C4 channels. TRPC1/4/5 channel activities were assayed by measuring intracellular concentration of Ca²⁺ ([Ca²⁺]_i) and by patch‐clamp electrophysiology. Selectivity of AM237 was tested against TRPC3, TRPC6, TRPV4, or TRPM2 channels.Key Results: AM237 potently activated TRPC5:C5 channels (EC₅₀ 15–20 nM in [Ca²⁺]_i assay) and potentiated their activation by sphingosine‐1‐phosphate but suppressed activation evoked by (−)‐englerin A (EA). In patch‐clamp studies, AM237 activated TRPC5:C5 channels, with greater effect at positive voltages, but with lower efficacy than EA. Pico145 competitively inhibited AM237‐induced TRPC5:C5 activation. AM237 did not activate TRPC4:C4, TRPC4–C1, TRPC5–C1, TRPC1:C5, and TRPC1:C4 channels, or native TRPC1:C4 channels in A498 cells, but potently inhibited EA‐dependent activation of these channels with IC₅₀ values ranging from 0.9 to 7 nM. AM237 (300 nM) did not activate or inhibit TRPC3, TRPC6, TRPV4, or TRPM2 channels.Conclusions and Implications: This study suggests the possibility for selective activation of TRPC5 channels by xanthine derivatives and supports the general principle that xanthine‐based compounds can activate, potentiate, or inhibit these channels depending on subunit composition.

Detection of mechanical stress is essential for diverse biological functions including touch, audition, and maintenance of vascular myogenic tone. PIEZO1, a mechano-sensing cation channel, is widely expressed in neuronal and non-neuronal cells and is expected to be involved in important biological functions. Here, we examined the possibility that PIEZO1 is involved in the regulation of synovial sarcoma cell-viability. Application of a PIEZO1 agonist Yoda1 effectively induced Ca²⁺ response and cation channel currents in PIEZO1-expressing HEK (HEK-Piezo1) cells and synovial sarcoma SW982 (SW982) cells. Mechanical stress, as well as Yoda1, induced the activity of an identical channel of conductance with 21.6 pS in HEK-Piezo1 cells. In contrast, Yoda1 up to 10 μM had no effects on membrane currents in HEK cells without transfecting PIEZO1. A knockdown of PIEZO1 with siRNA in SW982 cells abolished Yoda1-induced Ca²⁺ response and significantly reduced cell cell-viability. Because PIEZO1 is highly expressed in SW982 cells and its knockdown affects cell-viability, this gene is a potential target against synovial sarcoma.