1,25-(OH)D protects Schwann cells against advanced glycation end products-induced apoptosis through PKA-NF-κB pathway.

Aims: To explore the effect and mechanism of 1, 25-(OH)D on Schwann cell apoptosis induced by advanced glycation end products.

Main Methods: Schwann cells, isolated from rodent sciatic nerve were incubated with AGE-modified bovine serum albumin(AGE) to mimic diabetic conditions and 1,25-(OH)D was used as protector. Cell apoptosis was detected by PI/Annexin-V staining, caspase 3 activity assay and western blotting for caspase 3 and PARP. The activation of protein kinase A (PKA) and nuclear factor kappa-B (NF-κB) was evaluated by western blot. Immunofluorescent staining was used for intercellular location of NF-κB. Cytokine secretion was evaluated by enzyme-linked immunosorbent assay.

Key Findings: Schwann cell apoptosis accelerated after incubating with AGE. However, if combining 1,25-(OH)D with AGE, apoptosis decreased significantly. 1,25-(OH)D enhanced PKA activity, but inhibited AGE-induced nuclear translocation of NF-κB. Furthermore, PKA activator (8-bromoadenoside cyclic adenoside monophosphate, 8-Br-cAMP) or NF-κB inhibitor (caffeic acid phenethyl ester, CAPE) could reduce the apoptosis, decreased cleaved caspase 3 and cleaved PARP, suggesting the involvement of PKA and NF-κB pathways in the protection of 1,25-(OH)D on Schwann cells. Moreover, 8-Br-cAMP and CAPE could inhibit AGE-induced secretion of interleukin(IL)-1β, prostaglandin E2(PEG2) and cyclooxygenase 2(COX2). Interestingly, 8-Br-cAMP decreased phospho-NF-κB and inhibited nucleus translocation of NF-κB. It hinted at the regulation of PKA to NF-κB. Finally, a pre-treatment of H-89 (an inhibitor of PKA) could block the protection of 1,25-(OH)D on cell apoptosis. In conclusion, 1,25-(OH)D could protect Schwann cell against AGE-induced apoptosis through PKA/NF-κB pathway.

Significance: These findings provide experimental rationales for using vitamin D for diabetic neuropathy.