Pituitary Adenylate Cyclase Activating Polypetptide (PACAP) is a peptide hormone known to regulate energy homeostasis1. Mice lacking PACAP are cold sensitive and have impaired adrenergic-induced thermogenesis2-4. Interestingly, Pacap null mice can survive cold housing if acclimated slowly, similar to what was observed in UCP1 deficient mice4,5. We hypothesized that Pacap-/- mice employ alternate thermogenic pathways to compensate for impaired adaptive thermogenesis and assessed shivering thermogenesis and UCP1-dependent and UCP1-independent adaptive thermogenesis in male and female Pacap-/- and Pacap+/+ with cold acclimation (4°C). Assessment of oxidative fibres in skeletal muscles and behavioural observations did not show evidence of prolonged shivering in male or female Pacap-/- mice during cold acclimation compared to Pacap+/+ mice. We did however observe morphological and molecular differences in adipose tissues of Pacap-/- mice compared to Pacap+/+ mice that were distinct in males and females. Cold-acclimated, female Pacap-/- mice had decreased induction of UCP1 protein in intrascapular brown fat (iBAT), yet had a significantly higher beiging and UCP1 immunoreactivity (ir) in gonadal white fat (gWAT) compared to female Pacap+/+ mice. Furthermore, beiging was observed in inguinal white fat (ingWAT) and gWAT of female Pacap-/- mice housed at thermoneutrality (30°C), a finding not observed in Pacap+/+ control mice. Unlike female mice, we did not observe impaired UCP1 induction in iBAT of male Pacap-/- mice compared to Pacap+/+ mice, and this was associated with negligible UCP1-ir in male gWAT similar to wildtype controls. Despite previous work that has established impaired adaptive thermogenesis in Pacap-/- mice4, we show here that UCP1 protein can be induced in adipose tissues of Pacap-/- mice during cold acclimation, although to a lesser degree or in a different pattern compared to Pacap+/+ control mice. Taken together, this work suggests that while PACAP is clearly involved in regulating thermoregulation, it is not required for cold-induced UCP1 expression. In addition, this work highlights sexual dimorphism in adipose tissue remodeling and induction of thermogenesis with cold acclimation. References: (1) Rudecki AP, et al. Trends Endocrinol Metab. 2016;27(9), 620–632. (2) Gray SL, et al. J Mol Endocrinol. 2001;15(10), 1739–1747. (3) Gray SL, et al. J Endocrinol. 2002;143(10), 3946–3954. (4) Diané A, et al. J Endocrinol. 2014;222, 327–339. (5) Golozoubova V, et al. FASEB J. 2001;15, 2048–2050.