Garcinol promotes neurogenesis in rat cortical progenitor cells through the duration of extracellular signal-regulated kinase signaling

Garcinol is a polyisoprenylated benzophenone derivative found in Garcinia indica fruit rind and other species. The potential antioxidative and neuroprotective effects of garcinol in rat cortical astrocyte were demonstrated in our laboratory recently. Here, the effects of garcinol on the neuritogenesis process in cultured cortical progenitor cells were investigated to understand the roles of garcinol in neuronal survival and differentiation. These cells, derived from embryonic day 17 rats, differentiated into EGF-responsive neural precursor cells, would further form neurospheres. Our data exhibited garcinol induced neurite outgrowth in early developing EGF-treated neurospheres and significantly enhanced the expression of neuronal proteins, microtubule-associated protein 2 (MAP-2), and glial fibrillary acidic protein (GFAP). Furthermore, the neuronal marker, high-molecular-weight subunit of neurofilaments (NFH), was highly expressed after 5 μM garcinol treatment in neural precursor cells for 20 days. To identify the extracellular mechanism, rat cortical progenitor cells were treated garcinol and accordingly mediated the sustained activation of extracellular signal-regulated kinase (ERK) for different periods up to 20 h. In this regard, NMDA receptor-mediated calcium influx led to excitotoxic death and activated tyrosine phosphatase which limited the duration of ERK in cultured neurons. MK801, the NMDA receptor antagonist, treatment also induced the sustained phosphorylation of ERK and therefore enhanced neuronal survival. In our observation, garcinol treatment reduced growth factor deprivation-mediated cell death and nuclear import of C/EBPβ levels. Noteworthy, garcinol could promote neurite outgrowth in EGF-responsive neural precursor cells and modulate the ERK pathway in the enhancement of neuronal survival.