Receptors for NPY and PACAP differ in expression and activity during adipogenesis in the murine 3T3‐L1 fibroblast cell line

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Abstract
Background and purpose: Neuropeptides are involved in the regulation of food intake in the central nervous system, but they might also act on peripheral fat tissue via neuropeptide receptors. Experimental approach: We investigated the receptor expression and activity of pituitary adenylate cyclase-activating polypeptide (PACAP) and of neuropeptide Y at the mRNA and protein levels in the 3T3-L1 fibroblast line during differentiation into adipocytes. Intracellular calcium concentration was measured by calcium imaging. Key results: The PACAP receptors PAC1 and VPAC2 as well as the neuropeptide Y1 receptor were expressed at the mRNA level in fibroblasts, pre-adipocytes and adipocytes. The mRNA profile of the PAC1 receptor isoforms showed the HOP sequence, whereas the HIP-isoform was present in subconfluent 3T3-L1 fibroblasts only. At the protein level, the mature 3T3-L1 adipocytes produced the PAC1 and Y1 receptors; only the PAC1 receptor showed carbohydrate residues. Both neuropeptides induced an increase of intracellular calcium in mature adipocytes, which was absent in the precursor cells. These changes in calcium were mediated by Y1 and PAC1 receptors as demonstrated by the effects of specific receptor agonists and antagonists. Conclusions and implications: As the PAC1-HOP receptor variant seems to be responsible for PACAP-mediated calcium influx in many cell types, the HOP sequence might also mediate the increase in intracellular calcium in adipocytes. Because a high intracellular calcium level is associated with lipogenesis, peptidergic innervation of adipose tissue might be involved in stress-induced obesity. British Journal of Pharmacology (2009) 157, 620–632; doi:10.1111/j.1476-5381.2009.00164.x; published online 27 April 2009