Salt-induced vascular damage in hypertension involves redox activation of PARP/TRPM2 signalling and inflammasome assembly

BACKGROUND
Excess sodium intake induces vascular dysfunction. Molecular mechanisms underlying this are unclear. Here we investigated the role of reactive oxygen species (ROS), Ca2+ signaling and inflammation in salt-induced vascular injury, focusing on the interplay between redox-sensitive Poly(ADP-ribose) polymerase (PARP), which activates transient receptor potential melastatin 2 (TRPM2) Ca2+ channel, and nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome. Specifically, we sought to determine if salt excess induces a pro-oxidant environment, leading to PARP-induced TRPM2 activation and increased Ca2+ influx, inflammasome assembly, and consequent vascular damage.

METHODS
Vascular smooth muscle cells (VSMCs) from rats and humans were exposed to normal NaCl (140 mM) and high-salt conditions (180 mM).

RESULTS
High salt increased ROS generation, PARP activation, and TRPM2-mediated Ca2+ transients. Osmotic controls had no effect on these processes. High-salt medium promoted the release of pro-inflammatory cytokines interleukin-18 and interleukin-1β and increased phosphorylation of myosin light chain (MLC) in VSMCs. These effects were attenuated by inhibitors of PARP (Olaparib), TRPM2 (8-Br-cADPR), and NLRP3 inflammasome (MCC950). To validate these findings in in vivo, mice were subjected to a high-salt diet (4% NaCl, 5 weeks), resulting in elevated blood pressure and vascular remodeling and dysfunction. Exposure of vessels to olaparib and MCC950 attenuated the hypercontractility associated with a high-salt diet.

CONCLUSIONS
Salt-induced vascular injury in hypertension involves ROS generation in VSMCs leading to activation of the PARP/TRPM2 axis, increased Ca2+ influx, NLRP3 activation, and vascular injury. Our study provides new insights into molecular pathways involved in high-salt diet-induced vascular dysfunction, important in hypertension.