White adipose tissue (WAT) is composed of mature adipocytes and a stromal vascular fraction (SVF), which contains a variety of cells, including immune cells that vary among the different WAT depots. Growth hormone (GH) impacts immune function and adiposity in an adipose depot-specific manner. However, its effects on WAT immune cell populations remain unstudied. Bovine GH transgenic (bGH) mice are commonly used to study the in vivo effects of GH. These giant mice have an excess of GH action, impaired glucose metabolism, decreased adiposity, increased lean mass, and a shortened lifespan. Therefore, the purpose of this study was to characterize the WAT depot-specific differences in immune cell populations in the presence of excess GH in vivo. Three WAT depots were assessed: inguinal (sc), epididymal (EPI), and mesenteric (MES). Subcutaneous and MES bGH WAT depots showed a significantly higher number of total SVF cells, yet only MES bGH WAT had higher leukocyte counts compared with control samples. By means of flow cytometry analysis of the SVF, we detected greater macrophage and regulatory T-cell infiltration in sc and MES bGH WAT depots compared with controls. However, no differences were observed in the EPI WAT depot. RNA-sequencing confirmed significant alterations in pathways related to T-cell infiltration and activation in the sc depot with fewer significant changes in the EPI bGH WAT depot. These findings collectively point to a previously unrecognized role for GH in influencing the distribution of WAT immune cell populations in a depot-specific manner.

Acromegaly is associated with an increased incidence of cardiovascular disease. Transgenic mice expressing bovine GH (bGH) gene have previously been used to examine the effects of chronic GH stimulation on cardiovascular function. Results concerning systolic blood pressure (SBP) in bGH mice are conflicting. We hypothesized that these discrepancies may be the result of the various ages of the mice used in previous studies. In the current study, SBP was assessed monthly in male bGH mice from 3-12 months of age. Factors known to alter blood pressure were assessed during this time and included: levels of brain natriuretic peptide (BNP) and glucose homeostasis markers, and renal levels of angiotensin-converting enzyme 2 and endothelial nitric oxide synthase. Beginning at 6 months of age bGH had increased SBP compared with wild-type controls, which remained elevated through 12 months of age. Despite having increased blood pressure and cardiac BNP mRNA, bGH mice had decreased circulating levels of BNP. Additionally, bGH mice had an age-dependent decline in insulin levels. For example, they were hyperinsulinemic at 3 months, but by 11 months of age were hypoinsulinemic relative to wild-type controls. This decrease in insulin was accompanied by improved glucose tolerance at 11 months. Finally, both angiotensin-converting enzyme 2 and endothelial nitric oxide synthase expression were severely depressed in kidneys of 11-month-old bGH mice. These results indicate that elevated SBP in bGH mice is dependent on age, independent of insulin resistance, and related to alterations in both the natriuretic peptide and renin-angiotensin systems.

Growth hormone (GH) influences adipocyte differentiation, but both stimulatory and inhibitory effects have been described. Adipose tissue-derived mesenchymal stem cells (AT-MSC) are multipotent, able to differentiate into adipocytes, among other cells. Canonical Wnt/β-catenin signaling activation impairs adipogenesis. The aim of this study was to elucidate the role of GH on AT-MSC adipogenesis using cells isolated from male GH receptor gene knockout (GHRKO), bovine GH transgenic (bGH) and wild-type littermate control (WT) mice. AT-MSC from subcutaneous (sc), epididiymal (epi), and mesenteric (mes) AT depots were identified and isolated by flow cytometry (PDGFRα+Sca-1+CD45−Ter119− cells). Their in vitro adipogenic differentiation capacity was determined by cell morphology and real-time RT-PCR. Using identical in vitro conditions, adipogenic differentiation of AT-MSC was only achieved in the sc depot, but not in epi and mes depots. Notably, we observed an increased differentiation in cells isolated from sc-GHRKO and an impaired differentiation of sc-bGH cells compared with sc-WT cells. Axin-2, a marker of Wnt/β-catenin activation, was increased in mature sc-bGH adipocytes suggesting that activation of this pathway may be responsible for the decreased adipogenesis. Thus, we demonstrate that 1) adipose tissue in mice has a well-defined population of Sca-1+PDGFRα+ MSC cells; 2) the differentiation capacity of AT-MSC varies from depot to depot regardless of GH genotype; 3) the lack of GH action increases adipogenesis in sc depot; and 4) activation of Wnt/β-catenin pathway might mediate the GH effect on AT-MSC. Taken together, our results suggest that GH diminishes fat mass, in part, by altering adipogenesis of MSC.