PGP and diabetes mellitus: In bone-marrow sensory fibers, a locus increasingly recognized as neuropathy-sensitive, STZ diabetes down-regulated nociceptor innervation; NGF gene therapy increased PGP 9.5+ and SP+ fiber densities, corrected nociceptor-mediated stem-cell mobilization after ischemic injury and improved healing, expanding the territory of NGF insufficiency beyond classical nerve targets [32].