Canonical transient receptor potential (TRPC) channels were identified as key players in maladaptive remodeling, with nuclear factor of activated T-cells (NFAT) transcription factors serving as downstream targets of TRPC-triggered Ca²⁺ entry in these pathological processes. Strikingly, the reconstitution of TRPC-NFAT signaling by heterologous expression yielded controversial results. Specifically, nuclear translocation of NFAT1 was found barely responsive to recombinant TRPC3, presumably based on the requirement of certain spatiotemporal signaling features. Here, we report efficient control of NFAT1 nuclear translocation in human embryonic kidney 293 (HEK293) cells by light, using a new photochromic TRPC benzimidazole activator (OptoBI-1) and a TRPC3 mutant with modified activator sensitivity. NFAT1 nuclear translocation was measured along with an all-optical protocol to record local and global Ca²⁺ pattern generated during light-mediated activation/deactivation cycling of TRPC3. Our results unveil the ability of wild-type TRPC3 to produce constitutive NFAT nuclear translocation. Moreover, we demonstrate that TRPC3 mutant that lacks basal activity enables spatiotemporally precise control over NFAT1 activity by photopharmacology. Our results suggest tight linkage between TRPC3 activity and NFAT1 nuclear translocation based on global cellular Ca²⁺ signals.

Introduction: Photopharmacology has recently emerged as a strategy for high-precision modulation of immune functions. Here we explored efficiency and specificity of interventions based on light-induced TRPC6 activation in the RBL-2H3 mast cell model.Results: Expression of TRPC6 fusion constructs in RBL-2H3 allowed for generation of temporally well-defined, cytosolic Ca²⁺ transients in response to photoisomerization of the TRPC6 actuator OptoBI-1. These Ca²⁺ signals originated exclusively from Ca²⁺ entry across the plasma membrane. Transient TRPC6 activation in response to UV pulses of 1s duration (3 mW/cm²) just exceeded the detection threshold for monitoring of Ca²⁺ signals within the TRPC6-jRGECO1a nano/microdomain. Activation of TRPC6-jRGECO1a by single, 1s UV light pulses was sufficient to trigger maximal cytosolic to nuclear translocation of NFATc1 (NFAT2) equivalent to the level generated by ionomycin (1 µM)-induced Ca²⁺ entry. TRPC6 photopharmacology enabled control over NFATc1 nuclear translocation devoid of any detectable degranulation responses.Conclusion: We report here the exceptionally efficient and specific modulation of mast cell activity by TRPC6 photopharmacology.

Apolipoprotein C3 (apoC3) is a key regulator of triglyceride metabolism and has emerged as a potential therapeutic target for reducing the risk of cardiovascular disease. However, its broader physiological functions are not fully understood. This study investigates the role of apoC3 in platelet function and thrombus formation. Interestingly, human apoC3 was found to rapidly inhibit platelet activation over the tested concentration range of 0.1–10 µg/mL, with significant effects observed at low concentrations and brief pre-incubation times (from 1 min). At a concentration of 10 µg/mL, apoC3 suppressed platelet activation by approximately 70% in response to ADP and by approximately 40% in response to collagen stimulation. Depleting apoC3 from human serum enhanced platelet aggregation by more than 25 % (1.28 ± 0.19 vs. vehicle), indicating an endogenous regulatory function of apoC3. Mechanistically, apoC3 binding to platelets reduced both GPIIb/IIIa activation and P-selectin expression by around 20%. ApoC3 binding to platelets increased when platelets were activated by ADP and was partially mediated by GPIIb/IIIa, implicating this integrin as a functionally relevant receptor. Taken together, these findings reveal a novel link between apoC3 and platelet biology with potential implications for thrombotic risk and vascular homeostasis.