β-Catenin Regulates Wound Healing and IL-6 Expression in Activated Human Astrocytes

Reactive astrogliosis is prominent in most neurodegenerative disorders and is often associated with neuroinflammation. The molecular mechanisms regulating astrocyte-linked neuropathogenesis during injury, aging and human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) are not fully understood. In this study, we investigated the implications of the wingless type (Wnt)/beta-catenin signaling pathway in regulating astrocyte function during gliosis. First, we identified that HIV-associated inflammatory cytokines, interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha induced mediators of the Wnt/beta-catenin pathway including beta-catenin and lymphoid enhancer-binding factor (LEF)-1 expression in astrocytes. Next, we investigated the regulatory role of beta-catenin on primary aspects of reactive astrogliosis, including proliferation, migration and proinflammatory responses, such as IL-6. Knockdown of beta-catenin impaired astrocyte proliferation and migration as shown by reduced cyclin-D1 levels, bromodeoxyuridine incorporation and wound healing. HIV-associated cytokines, IL-1beta alone and in combination with TNF-alpha, strongly induced the expression of proinflammatory cytokines including C-C motif chemokine ligand (CCL)2, C-X-C motif chemokine ligand (CXCL)8 and IL-6; however, only IL-6 levels were regulated by beta-catenin as demonstrated by knockdown and pharmacological stabilization. In this context, IL-6 levels were negatively regulated by beta-catenin. To better understand this relationship, we examined the crossroads between beta-catenin and nuclear factor (NF)-kappaB pathways. While NF-kappaB expression was significantly increased by IL-1beta and TNF-alpha, NF-kappaB levels were not affected by beta-catenin knockdown. IL-1beta treatment significantly increased glycogen synthase kinase (GSK)-3beta phosphorylation, which inhibits beta-catenin degradation. Further, pharmacological inhibition of GSK-3beta increased nuclear translocation of both beta-catenin and NF-kappaB p65 into the nucleus in the absence of any other inflammatory stimuli. HIV+ human astrocytes show increased IL-6, beta-catenin and NF-kappaB expression levels and are interconnected by regulatory associations during HAND. In summary, our study demonstrates that HIV-associated inflammation increases beta-catenin pathway mediators to augment activated astrocyte responses including migration and proliferation, while mitigating IL-6 expression. These findings suggest that beta-catenin plays an anti-inflammatory role in activated human astrocytes during neuroinflammatory pathologies, such as HAND.