Telmisartan inhibits microglia-induced neurotoxic A1 astrocyte conversion via PPARγ-mediated NF-κB/p65 degradation

Abstract

Astrocytes are crucially involved in neuroinflammation. Activated astrocytes exhibit at least two phenotypes, A1 (neurotoxic) and A2 (neuroprotective). The A1 phenotype is the major reactive astrocyte phenotype involved in aging and neurodegenerative diseases. Telmisartan, which is an antihypertensive agent, is a promising neuroprotective agent. This study aimed to investigate the effects of telmisartan on the phenotype of reactive astrocytes. Astrocytes were activated by culturing with the conditioned medium derived from lipopolysaccharide-stimulated microglia. This conditioned medium induced early, transient A2 astrocyte conversion (within 24 h) and late, sustained A1 conversion (beginning at 24 h and lasting up to 7 days), with a concomitant increase in the production of pro-inflammatory cytokines (interleukin [IL]-1β, tumor necrosis factor [TNF]α, and IL-6) and phosphorylation of nuclear factor-κB (NF-κB)/p65. Telmisartan treatment promoted and inhibited A2 and A1 conversion, respectively. Telmisartan reduced total and phosphorylated p65 protein levels. Losartan, a specific angiotensin II type-1 receptor (AT1R) blocker, did not influence the reactive state of astrocytes. Additionally, AT1R activation by angiotensin II did not induce the expression of pro-inflammatory cytokines and A1/A2 markers, indicating that the AT1R signaling pathway is not involved in the astrocyte-mediated inflammatory response. A peroxisome proliferator-activated receptor γ (PPARγ) antagonist reversed the effects of telmisartan. Moreover, telmisartan-induced p65 downregulation was reversed by the proteasome inhibitor MG132. These results indicate that telmisartan suppresses activated microglia-induced neurotoxic A1 astrocyte conversion through p65 degradation. Our findings contribute towards the elucidation of the anti-inflammatory activity of telmisartan in brain disorders.

Keywords: Astrocytes; Microglia; Proliferator-activated receptor γ; Telmisartan; angiotensin II type-1 receptor.