PDX1, a transcription factor essential for organ differentiation, regulates SERCA-dependent Ca2+ homeostasis in sensory neurons

Pancreatic and duodenal homeobox 1 (PDX1) is a transcription factor required for the development and differentiation of the pancreas. Previous studies indicated that PDX1 expression was restricted to the gastrointestinal tract. Using a cre-dependent reporter, we observed PDX1-dependent expression of tdtomato (PDX1-tom) in a subpopulation of sensory nerves. Many of these PDX1-tom afferents expressed the neurofilament 200 protein and projected to the skin. Tdtomato-labeled terminals were associated with hair follicles in the form of longitudinal and circumferential lanceolate endings suggesting a role in tactile and proprioceptive perception. To begin to examine the functional significance of PDX1 in afferents, we used Fura-2 imaging to examine calcium (Ca²⁺) handling under naïve and nerve injury conditions. Neuropathic injury is associated with increased intracellular Ca²⁺ signaling that in part results from dysregulation of the sarco/endoplasmic reticulum calcium transport ATPase (SERCA). Here we demonstrate that under naïve conditions, PDX1 regulates expression of the SERCA2B isoform in sensory neurons. In response to infraorbital nerve injury, a significant reduction of PDX1 and SERCA2B expression and dysregulation of Ca²⁺ handling occurs in PDX1-tom trigeminal ganglia neurons. The identification of PDX1 expression in the somatosensory system and its regulation of SERCA2B and Ca²⁺ handling provide a new mechanism to explain pathological changes in primary afferents that may contribute to pain associated with nerve injury.