Nitric Oxide-NGF Mediated PPTA/SP, ADNP, and VIP Expression in the Peripheral Nervous System

Nerve growth factor (NGF)-deprivation or axotomy of dorsal root ganglion (DRG) neurons causes stress, which they cope by triggering various mechanisms. Among several molecular changes, in the present study, we demonstrate preprotachykinin-A–substance P (PPTA–SP) and activity-dependent neuroprotective protein–vasoactive intestinal peptide (ADNP–VIP) expression pattern using DRG neurons–Schwann cells coculture and axotomy model. In the presence of NGF, DRG cultures showed high levels of PPTA and ADNP mRNA expression, which were significantly suppressed in the absence of NGF and/or nitric oxide synthase (NOS) inhibition by NG-nitro-l-arginine methyl ester (l-NAME), suggesting that both NGF and nitric oxide (NO) can regulate PPTA and ADNP expression. However, treating coculture with NO donor, diethylenetriamine nitric oxide (DETA–NO) did not increase PPTA and ADNP expression in the presence or absence of NGF, although there was a marginal increase in ADNP expression in the absence of NGF. NGF-deprivation increases endogenous NO; thus, DETA–NO had no further effect on PPTA and ADNP expression. Alternatively, NGF produced from NO-stimulated Schwann cells influence gene expression. In addition, interestingly, DETA–NO treatment of Schwann cells alone suppresses both PPTA and ADNP, suggesting differential response of DRG neurons–Schwann cells coculture to DETA–NO. SP and ADNP immunostaining of axotomized DRGs revealed significant reduction in SP and ADNP compared to intact DRG, which was partially recovered in neuronal NOS blocker, 7-nitroindazole (7-NI)-treated DRGs, particularly intense ADNP staining in satellite glia. As ADNP is VIP-responsive gene, we further explored VIP expression in DRGs. Axotomy increased VIP in DRG neurons, but 7-NI treatment caused intense VIP staining in satellite glia. These observations suggest a complex interaction of NO–NGF with PPTA/SP and ADNP–VIP in neuron–glial communication when neurons are stressed.