Adiponectin is an abundantly circulating adipokine, orchestrating its effects through two 7-transmembrane receptors (AdipoR1 and AdipoR2). Steroidogenesis is regulated by a variety of neuropeptides and adipokines. Earlier studies have reported adipokine mediated steroid production. A key rate-limiting step in steroidogenesis is cholesterol transportation across the mitochondrial membrane by steroidogenic acute regulatory protein (StAR). Several signalling pathways regulate StAR expression. The actions of adiponectin and its role in human adrenocortical steroid biosynthesis are not fully understood. The aim of this study was to investigate the effects of adiponectin on StAR protein expression, steroidogenic genes, and cortisol production and to dissect the signalling cascades involved in the activation of StAR expression. Using qRT-PCR, Western blot analysis and ELISA, we have demonstrated that stimulation of human adrenocortical H295R cells with adiponectin results in increased cortisol secretion. This effect is accompanied by increased expression of key steroidogenic pathway genes including StAR protein expression via ERK1/2 and AMPK-dependent pathways. This has implications for our understanding of adiponectin receptor activation and peripheral steroidogenesis. Finally, our study aims to emphasise the key role of adipokines in the integration of metabolic activity and energy balance partly via the regulation of adrenal steroid production. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.
Model development. We performed an iterative, balanced optimization analysis to determine the ability of ToxCast HTS assays to correctly classify the results of guideline endocrine-related assays while maintaining balance between sensitivity and specificity. The process for this analysis is illustrated in Figure 2 . Because each HTS endocrine MOA may have multiple ToxCast HTS assays, we used disjunctive logic employing varied weight-of-evidence thresholds to determine optimal predictive performance. This model tested variable thresholds for the HTS ToxCast assay results represented as unweighted binary data, while the guideline or non-guideline endocrine-related assay results remained static. Initially, the model began with a threshold criterion of one positive ToxCast HTS assay out of the total number of ToxCast HTS assays for a chemical to be considered to perturb a given MOA. Once calculated, the model was then re-run with increasing increments of one assay until all ToxCast HTS assays for a given endocrine MOA were required to be positive for a chemical to be considered to perturb the given MOA. As the threshold for a positive call was increased, a larger weight of evidence was required for a chemical to be considered a “hit” for perturbing the given endocrine MOA. An exception was made for guideline pubertal studies and the ToxCast NVS_NR_hAR assay. Guideline pubertal studies test for effects that can arise through multiple different endocrine-related pathways. For this reason, if a chemical was considered positive in the pubertal assay and the result conflicted with other guideline studies (., receptor binding, reporter gene), the pubertal assay was not included in the weight of evidence. The ToxCast NVS_NR_hAR assay is a human androgen receptor binding assay in the LNCaP prostatic cell line. The androgen receptor in this cell line is known to bind to steroid hormones other than androgens ( Veldscholte et al. 1992 ). For this reason, if a compound was negative in all other HTS-A assays, the result for the NVS_NR_hAR assay was not included in the weight-of-evidence.