Chronic lipopolysaccharide exposure promotes cognitive impairments by activating TRPC6-AIM2 inflammasome signaling and the regulation of ginsenoside Rg1 in Trpc6-/- mice.

Abstract

Background: Chronic neuroinflammation is a pivotal pathogenesis in neurodegenerative diseases (NDDs). Transient receptor potential canonical protein 6 (TRPC6) has an essential role in the maintenance of calcium homeostasis in cells. Our previous study indicated that TRPC6 signaling is involved in Aβ deposition and NLRP1 inflammasome activation in type 2 diabetes mellitus-associated cognitive dysfunction. However, whether TRPC6 signaling contributes to chronic lipopolysaccharide (LPS)-induced neuroinflammatory injury and the mechanism remain unclear.

Methods: In this study, male mice received intraperitoneal injections of LPS (200 µg/kg) for 21 days to induce a chronic neuroinflammation model. The open field test, hole-board test, and Morris water maze were conducted to evaluate cognitive function. The H&E and Nissl staining was employed to examine neuronal injury. The immunofluorescence, western blotting, or q-PCR were used to analyze TRPC6, AIM2 inflammasome expression, and Nrf2 activation. The fluorescent probes and calcium imaging were performed to assess ROS accumulation and calcium dysregulation in LPS-induced HT22 neuron cells.

Results: Chronic LPS exposure induced behavioral deficits in locomotion, exploratory behavior, and learning and memory, and neuronal damages with less expressions of PSD95 and Synaptophysin in mice. Mechanistically, LPS exposure significantly increased ROS production, TRPC6 expression and calcium overload, and induced AIM2 inflammasome activation in vivo or in vitro. While Trpc6 knockout could significantly improve LPS-induced cognitive dysfunction and neuronal injuries, inhibit TRPC6-mediated calcium overload, and downregulate the expressions of AIM2, caspase-1, IL-1β, IL-6, caspase-3 and Bax in vivo or in vitro. Additionally, Rg1 treatment significantly inhibited calcium overload and AIM2 inflammasome activation in LPS-induced HT22 cells. More importantly, Rg1 significantly activated Nrf2 signaling and reduced ROS production in LPS-induced mice or HT22 cells.

Conclusions: Trpc6 knockout can improve chronic LPS-induced neuroinflammation and injury by inhibiting TRPC6-AIM2 inflammasomes. While Rg1 treatment can alleviate LPS-induced neuroinflammation and injury not only by inhibiting TRPC6-AIM2 inflammasomes activation but also activating Nrf2 signaling.