Sema3a is produced by brown adipocytes and its secretion is reduced following cold acclimation

Heat production in brown adipose tissue (BAT) and brown adipocyte recruitment depend heavily on BAT vascular and parenchymal sympathetic and sensory innervation. The expression and distribution of Sema3a, a recently discovered chemorepellent neuronal factor active on both sympathetic and sensory peripheral nerves, were studied in interscapular rat BAT. In rats maintained in thermoneutral conditions, brown adipocytes produced both active isoforms of Sema3a and showed a distinct peripheral polarized immunostaining pattern. This suggests a role for Sema3a secreted by brown adipocytes in the guidance of axons toward their correct targets. In cold-acclimated rats, where parenchymal nerve density is higher, both the expression and the immunostaining of the two active isoforms were slightly but significantly reduced and the distinct staining pattern was not observed. These data suggest that the secretion of Sema3a is inhibited in the brown adipocytes of cold-acclimated rats. Thus, Sema3a could play a role in the plastic adjustment of BAT innervation observed in different conditions of functional demand.