Tyrosine Hydroxylase Neurons Regulate Growth Hormone Secretion via Short-Loop Negative Feedback

Abstract

Classical studies suggest that growth hormone (GH) secretion is controlled by negative-feedback loops mediated by GH-releasing hormone (GHRH)-or somatostatin-expressing neurons. Catecholamines are known to alter GH secretion and neurons expressing TH are located in several brain areas containing GH-responsive cells. However, whether TH-expressing neurons are required to regulate GH secretion via negative-feedback mechanisms is unknown. In the present study, we showed that between 50% and 90% of TH-expressing neurons in the periventricular, paraventricular, and arcuate hypothalamic nuclei and locus ceruleus of mice exhibited STAT5 phosphorylation (pSTAT5) after an acute GH injection. Ablation of GH receptor (GHR) from TH cells or in the entire brain markedly increased GH pulse secretion and body growth in both male and female mice. In contrast, GHR ablation in cells that express the dopamine transporter (DAT) or dopamine b-hydroxylase (DBH; marker of noradrenergic/adrenergic cells) did not affect body growth. Nevertheless, less than 50% of TH-expressing neurons in the hypothalamus were found to express DAT. Ablation of GHR in TH cells increased the hypothalamic expression of Ghrh mRNA, although very few GHRH neurons were found to coexpress TH-and GH-induced pSTAT5. In summary, TH neurons that do not express DAT or DBH are required for the autoregulation of GH secretion via a negative-feedback loop. Our findings revealed a critical and previously unidentified group of catecholaminergic interneurons that are apt to sense changes in GH levels and regulate the somatotropic axis in mice.

Neurochemical phenotype of growth hormone‐responsive cells in the mouse paraventricular nucleus of the hypothalamus

“…Thus, nowadays it is well‐accepted that leptin responsive neurons can be identified by the phosphorylation of STAT3 (Donato Jr. et al, 2009; Munzberg, Huo, Nillni, Hollenberg, & Bjorbaek, 2003; Nagaishi et al, 2014; Scott et al, 2009), whereas prolactin responsive neurons can be visualized through pSTAT5 staining (Brown et al, 2010; Furigo et al, 2014). Regarding GH, our research group was pioneer in using the capacity of an acute systemic injection of GH to induce pSTAT5 in the brain, allowing the visualization of neurons that are directly responsive to this hormone (Bohlen et al, 2019; Furigo et al, 2017; Furigo, de Souza, et al, 2019a; Furigo, Teixeira, et al, 2019b; Quaresma et al, 2019; Silveira et al, 2019; Teixeira et al, 2019; Wasinski et al, 2020). Although this method may present shortfalls since pSTAT5 can be induced by multiple cytokines (Teglund et al, 1998) and theoretically some cells may not be responsive to GH even if they express GHR, the complete absence of staining in the PVH of PBS‐injected mice clearly demonstrates the specificity of our strategy to identify GH‐responsive cells.…”

“…However, our research group mapped the distribution of GH‐responsive cells in the mouse brain (Furigo, Metzger, Teixeira, Soares, & Donato Jr., 2017) and found a much broader distribution of cells that respond directly to GH than previously acknowledged. Besides the regulation of the somatotropic axis (Wasinski et al, 2020), GH action in the hypothalamus has been recently associated with the central control of metabolism (Wasinski, Frazão, & Donato, 2019). GH receptor (GHR) ablation in different neural populations promotes changes in food intake, energy expenditure, body adiposity, glucose homeostasis, and remarkably also in the response to situations of metabolic stress (Bohlen et al, 2019; Furigo et al, 2019a; Furigo et al, 2019b; Quaresma et al, 2019; Teixeira et al, 2019).…”

Central Regulation of Metabolism by Growth Hormone

“…GHR is also amply expressed in the arcuate nucleus (ARH), which is the principal hypothalamic region that hosts GHRH-expressing neurons [ 28 , 31 ]. However, only a small percentage of GHRH neurons seem to contain GHR [ 32 , 33 ], whereas Ghr mRNA is abundantly detected in ARH neurons that express neuropeptide Y (NPY) [ 34 , 35 ]. Our research group has used the capacity of an acute GH injection to induce phosphorylation of the signal transducer and activator of transcription-5 (pSTAT5) as an alternative method to identify GH-responsive neurons [ 36 , 37 ].…”

“…In another study, our research group disclosed that several neuronal populations that express TH are responsive to GH, including neurons in the ARH, PVH ( Figure 3 ), PV and locus coeruleus (LC) [ 33 ]. Of note, LC is the major source of noradrenergic projections to the forebrain [ 107 ], which are vital for the control of physiological responses to stress.…”

Growth hormone receptor (GHR)-expressing neurons in the hypothalamic arcuate nucleus regulate glucose metabolism and energy homeostasis

“…Evidence for the importance of GH-responsive neurons in the hypothalamus in modulating metabolism was reported in several studies (35)(36)(37)(38). We have recently identified a unique population of nutrient-sensing leptin receptor (LepRb)-GHR expressing neurons that regulate hepatic glucose production and lipid metabolism, suggesting that these neurons are crucial for the metabolic functions of GHR-neurocircuitry (18).…”