Autocrine/paracrine role of inflammation-mediated calcitonin gene-related peptide and adrenomedullin expression in human adipose tissue

Human adipose tissue is a contributor to inflammation- and sepsis-induced elevation of serum procalcitonin (ProCT). Several calcitonin (CT) peptides, including ProCT, CT gene-related peptide ( CGRP), and adrenomedullin (ADM) are suspected mediators in human inflammatory diseases. Therefore, we aimed to explore the expression, interactions, and potential roles of adipocyte-derived CT peptide production. Expression of CT peptide-specific transcripts was analyzed by RT-PCR and quantitative real-time PCR in human adipose tissue biopsies and three different inflammation-challenged human adipocyte models. ProCT, CGRP, and ADM secretions were assessed by immunological methods. Adipocyte transcriptional activity, glycerol release, and insulin-mediated glucose transport were studied after exogenous CGRP and ADM exposure. With the exception of amylin, CT peptides were expressed in adipose tissue biopsies from septic patients, inflammation- activated mature explanted adipocytes, and macrophage-activated preadipocyte-derived adipocytes. ProCT and CGRP productions were significantly augmented in IL-1 beta and lipopolysaccharide-challenged mesenchymal stem cell-derived adipocytes but not in undifferentiated mesenchymal stem cells. In contrast, ADM expression occurred before and after adipogenic differentiation. Interferon-gamma coadministration inhibited IL-1 beta-mediated ProCT and CGRP secretion by 78 and 34%, respectively but augmented IL-1 beta-mediated ADM secretion by 50%. Exogenous CGRP and ADM administration induced CT, CGRP I, and CGRP II mRNAs and dose-dependently (10(-10) and 10(-6) M) enhanced glycerol release. In contrast, no CGRP- and ADM-mediated effects were noted on ADM, TNF alpha, and IL-1 beta mRNA abundances. In summary, CGRP and ADM are two differentially regulated novel adipose tissue secretion factors exerting autocrine/paracrine roles. Their lipolytic effect ( glycerol release) suggests a metabolic role in adipocytes during inflammation.