Reference gene recommendations and PACAP receptor expression in murine sympathetic ganglia of the autonomic nervous system that innervate adipose tissues after chronic cold exposure

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an important regulator of the stress response in mammals, influencing both the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS). PACAP has been reported to influence energy homeostasis, including adaptive thermogenesis, an energy burning process in adipose tissue regulated by the SNS in response to cold stress and overfeeding. While research suggests PACAP acts centrally at the level of the hypothalamus, knowledge of PACAP's role within the sympathetic nerves innervating adipose tissues in response to metabolic stressors is limited. This work shows, for the first time, gene expression of PACAP receptors in stellate ganglia and highlights some differential expression with housing temperature. Additionally, we present our dissection protocol, analysis of tyrosine hydroxylase gene expression as a molecular biomarker for catecholamine producing tissue and recommend three stable reference genes for the normalization of quantitative real time-polymerase chain reaction (qRT-PCR) data when working with this tissue. This study adds to information about neuropeptide receptor expression in peripheral ganglia of the sympathetic nervous system innervating adipose tissue and provides insight into PACAP's role in the regulation of energy metabolism.

Contribution of thermogenic mechanisms by male and female mice lacking pituitary adenylate cyclase-activating polypeptide in response to cold acclimation

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide critical to the regulation of the stress response, including having a role in energy homeostasis. Mice lacking PACAP are cold-sensitive and have impaired adrenergic-induced thermogenesis. Interestingly, Pacap null mice can survive cold housing if acclimated slowly, similar to observations in uncoupling protein 1 (UCP1)-deficient mice. We hypothesized that Pacap null mice use alternate thermogenic pathways to compensate for impaired adaptive thermogenesis when acclimated to cold. Observations of behavior and assessment of fiber type in skeletal muscles did not show evidence of prolonged burst shivering or changes in oxidative metabolism in male or female Pacap^-/- mice during cold acclimation compared with Pacap^+/+ mice. Despite previous work that has established impaired capacity for adaptive thermogenesis in Pacap null mice, adaptive thermogenesis can be induced in mice lacking PACAP to support survival with cold housing. Interestingly, sex-specific morphological and molecular differences in adipose tissue remodeling were observed in Pacap null mice compared with controls. Thus, sexual dimorphisms are highlighted in adipose tissue remodeling and thermogenesis with cold acclimation in the absence of PACAP.NEW & NOTEWORTHY This manuscript adds to the literature of endocrine regulation of adaptive thermogenesis and energy balance. It specifically describes the role of pituitary adenylate cyclase-activating polypeptide on the regulation of brown adipose tissue via the sympathetic nervous system with a focus on compensatory mechanisms of thermogenesis. We highlight sex-specific differences in energy metabolism.

Melanotan II, a melanocortin agonist, partially rescues the impaired thermogenic capacity of pituitary adenylate cyclase-activating polypeptide deficient mice

NEW FINDINGS

What is the central question of this study? Can chronic treatment of pituitary adenylate cyclase-activating polypeptide (PACAP) deficient mice with the melanocortin agonist melanotan II during cold acclimation rescue the impaired thermogenic capacity previously observed in PACAP deficient mice? What is the main finding and its importance? Using a genetic model of PACAP deficiency, this study provides evidence that PACAP acts upstream of the melanocortin system in regulating sympathetic nerve activity to brown adipose tissue in mice.

ABSTRACT

Impaired adipose tissue function in obesity, including reduced thermogenic potential, has detrimental consequences for metabolic health. Hormonal regulation of adaptive thermogenesis is being explored as a potential therapeutic target for human obesity. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide expressed in nuclei of the hypothalamus known to regulate energy expenditure, and functional studies reveal a role for PACAP in the central regulation of thermogenesis, although mechanisms are not well understood. We hypothesized that PACAP acts upstream of the melanocortin system to regulate sympathetic nerve activity to stimulate thermogenesis. To assess this, female PACAP^-/- and PACAP^+/+ mice were given daily peripheral injections of a melanocortin receptor agonist, melanotan II (MTII), for 3 weeks during cold acclimation, and the effect of MTII on thermogenic capacity and adipose tissue remodelling was examined by physiological and histological analyses. MTII partially rescued the impaired thermogenic capacity in PACAP^-/- mice as compared to PACAP^+/+ mice as determined by measuring noradrenaline-induced metabolic rate. In addition, MTII treatment during cold acclimation corrected the previously identified deficit in lipid utilization in response to adrenergic stimulation in PACAP^-/- null mice, suggesting impaired lipid mobilization may contribute to the impaired thermogenic capacity of PACAP^-/- mice. Results presented here provide physiological evidence to suggest that PACAP acts upstream of melanocortin receptors to facilitate sympathetically induced mechanisms of adaptive thermogenesis in response to cold acclimation.

SAT-583 Assessment of Thermoregulatory Pathways Induced in Male and Female Mice Lacking Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) in Response to Cold Acclimation

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 thermogenesis^2-4. Interestingly, Pacap null mice can survive cold housing if acclimated slowly, similar to what was observed in UCP1 deficient mice^4,5. 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.