α1-antitrypsin mitigates NLRP3-inflammasome activation in amyloid β1-42-stimulated murine astrocytes

Background: Neuroinflammation has an essential impact on the pathogenesis and progression of Alzheimer's disease (AD). Mostly mediated by microglia and astrocytes, inflammatory processes lead to degeneration of neuronal cells. The NLRP3-inflammasome (NOD-like receptor family, pyrin domain containing 3) is a key component of the innate immune system and its activation results in secretion of the proinflammatory effectors interleukin-1 beta (IL-1 beta) and interleukin-18 (IL-18). Under physiological conditions, cytosolic NLRP3-inflammsome is maintained in an inactive form, not able to oligomerize. Amyloid beta(1-42) (A beta(1-42)) triggers activation of NLRP3-inflammasome in microglia and astrocytes, inducing oligomerization and thus recruitment of proinflammatory proteases. NLRP3-inflammasome was found highly expressed in human brains diagnosed with AD. Moreover, NLRP3-deficient mice carrying mutations associated with familial AD were partially protected from deficits associated with AD. The endogenous protease inhibitor alpha 1-antitrypsin (A1AT) is known for its anti-inflammatory and anti-apoptotic properties and thus could serve as therapeutic agent for NLRP3-inhibition. A1AT protects neurons from glutamate-induced toxicity and reduces A beta(1-42)-induced inflammation in microglial cells. In this study, we investigated the effect of A beta(1-42)-induced NLRP3-inflammasome upregulation in primary murine astrocytes and its regulation by A1AT. Methods: Primary cortical astrocytes from BALB/c mice were stimulated with A beta(1-42) and treated with A1AT. Regulation of NLRP3-inflammasome was examined by immunocytochemistry, PCR, western blot and ELISA. Our studies included an inhibitor of NLRP3 to elucidate direct interactions between A1AT and NLRP3-inflammasome components. Results: Our study revealed that A1AT reduces A beta(1-42)-dependent upregulation of NLRP3 at the mRNA and protein levels. Furthermore, A1AT time-dependently mitigated the expression of caspase 1 and its cleavage product IL-1 beta in A beta(1-42)-stimulated astrocytes. Conclusion: We conclude that A beta(1-42)-stimulation results in an upregulation of NLRP3, caspase 1, and its cleavage products in astrocytes. A1AT time-dependently hampers neuroinflammation by downregulation of A beta(1-42)-mediated NLRP3-inflammasome expression and thus may serve as a pharmaceutical opportunity for the treatment of Alzheimer's disease.