Epidermal SIRT1 and BDNF modulate mechanical allodynia in mouse models of diabetic neuropathy

Diabetic neuropathy (DN) is a debilitating disorder characterized by mechanical allodynia and sensory loss. It has traditionally been considered a small-fiber neuropathy, defined by the loss of free nerve endings in the epidermis. Free nerve endings, however, are nociceptors which may not be the only sensor for mechanical pain. To investigate the role of mechanoreceptors, specifically Meissner corpuscles, in the development of diabetic mechanical allodynia, our study focused on the keratinocyte-secreted brain-derived neurotrophic factor (BDNF) and its transcriptional regulator sirtuin 1 (SIRT1). Wild-type DN mice demonstrated decreased SIRT1 deacetylase activity, leading to a decrease in BDNF expression and Meissner corpuscle densities in foot skin. Epidermal SIRT1 knockout (KO) mice developed exacerbated DN phenotypes including severe mechanical allodynia, markedly reduced Meissner corpuscles, and subcutaneous Aß axon degeneration. Among the major skin-derived neurotrophic factors, only BDNF was down-regulated in epidermal SIRT1 KO mice. With similar KO phenotypes, epidermal BDNF appeared to belong to the same pathway as SIRT1 in modulating diabetic mechanical allodynia. Furthermore, mice overexpressing epidermal SIRT1 showed BDNF up-regulation and improved DN phenotypes, supporting an important role of epidermal SIRT1 and BDNF in skin sensory apparatus regeneration and functional recovery in the setting of diabetes.