Berberine suppresses neuroinflammatory responses through AMP-activated protein kinase activation in BV-2 microglia.

The AMPK cascade is a sensor of cellular energy change, which monitors the AMP/ATP ratio to regulate cellular metabolism by restoring ATP levels, but its regulation of neuroinflammation mechanism remains unclear. Berberine, one of the major constituents of Chinese herb Rhizoma coptidis, has been shown to improve several metabolic disorders, such as obesity and type II diabetes. However, the effect of berberine on neuroinflammatory responses in microglia are poorly understood. This study shows that berberine represses proinflammatory responses through AMP-activated protein kinase (AMPK) activation in BV-2 microglia. Our findings also demonstrate that berberine significantly down-regulates LPS- or interferon (IFN)-gamma-induced nitric oxide synthase (iNOS) and cyclo-oxygenase-2 (COX-2) expression in BV-2 microglia cells. Berberine also inhibited LPS- or IFN-gamma-induced nitric oxide production. In addition, berberine effectively inhibited proinflammatory cytokines such as TNF-alpha, IL-1beta, and IL-6 expression. On the other hand, upon various inflammatory stimulus including LPS and IFN-gamma, berberine suppressed the phosphorylated of ERK but not p38 and JNK in BV-2 microglia. AMPK activation is catalyzed by upstream kinases such as LKB1 and Ca2+/calmodulin-dependent protein kinase kinase-II (CaMKK II). Moreover, berberine induced LKB1 (Ser428), CaMKII (Thr286), and AMPK (Thr172) phosphorylation, but not AMPK (Ser485). Furthermore, the inhibitory effect of berberine on iNOS and COX-2 expression was abolished by AMPK inhibition via Compound C, an AMPK inhibitor. Berberine-suppressed ERK phosphorylation was also reversed by Compound C treatment. Our data demonstrate that berberine significantly induces AMPK signaling pathways activation, which is involved in anti-neuroinflammation.