The expression of vesicular glutamate transporter 3 and vesicular monoamine transporter 2 induced by brain-derived neurotrophic factor in dorsal root ganglion neurons in vitro

Abstract

The vesicular glutamate transporter 3 (VGLUT3) and the vesicular monoamine transporter 2 (VMAT2) are expressed in dorsal root ganglion (DRG) neurons and play an important role in packing the neurotransmitter into synaptic vesicles. Brain-derived neurotrophic factor (BDNF) is one of the most profound known regulators of survival in the developing peripheral nervous system (PNS). Whether BDNF regulates the expression of VGLUT3 and VMAT2 in DRG neurons is still unclear. In the present study, primary cultured rat DRG neurons were used to evaluate the effects of BDNF on VGLUT3 and VMAT2 expression. The signaling pathways of the extracellular signal-regulated protein kinase 1/2 (ERK1/2), the phosphatidylinositol 3-kinase (PI3K)/Akt, and the phospholipase C-gamma (PLC-γ) involved in these effects were also determined. DRG neurons at 48h post-culture were incubated with BDNF and/or ERK1/2 inhibitor PD98059, PI3K inhibitor LY294002, and PLC-γ inhibitor U73122 for an additional 24h. After that, the neurite growth and growth-associated protein 43 (GAP-43) expressions after different doses of BDNF treatment were determined by immunofluorescent labeling. The expression of mRNA and protein of VGLUT3 and VMAT2 in different experimental conditions was assessed by real-time PCR, immunoblotting, and immunofluorescent labeling, respectively. The results showed that BDNF exposure promoted neurite growth and GAP-43 expression in DRG neurons in a dose-dependent manner. BDNF induced VGLUT3 upregulation through activation of PLC-γ signaling pathway. Although BDNF administration did not elevate the levels of VMAT2, the block of the PI3K/Akt or PLC-γ signaling pathways could inhibit VMAT2 expression in DRG neurons in the presence of BDNF. The knockdown of VGLUT3 or VMAT2 gene by siRNA did not affect the BDNF's effects on GAP-43 upregulation and neurite growth. The upregulation of VGLUT3 induced by BDNF might be that BDNF improved neuronal outgrowth status by promoting GAP-43 expression to stimulate neurite elongation. The contribution of distinct VGLUT3 and VMAT2 transporter expression induced by BDNF might be one of the mechanisms that BDNF regulates neuropathic pain. These data imply that BDNF signaling system might be a potential target on modifying distinct transporter-mediated biological effects of primary sensory neurons.