The influence of metabolic diseases such as obesity and diabetes on the function and morphology of the hypothalamic-pituitary-adrenal axis as well as on their progenitor and stem cells

The endocrine system involves communication among different tissues including the pancreas, adipocytes and components of the hypothalamic-pituitary-adrenal (HPA) axis. Diseases such as obesity and diabetes are major challenges in modern medicine with the brain-metabolic axis as a master regulator of the human body for sustaining homeostasis under metabolic stress. Metabolic inflammation and disease trigger sustained activation of the HPA axis. On the other hand, dysregulation of the sympatho-adrenomedullary system and frequent or chronic stimulation of the HPA axis may contribute to the current increase in metabolic disorders. The adrenals, as HPA end-effectors, are connected to the body’s metabolism and play a major role in the development of obesity and diabetes. Moreover, both the pituitary and the adrenal gland are highly plastic organs, which adapt and regenerate continuously during lifetime and due to metabolic dysfunction. Resident progenitor and stem cell contribution to postnatal homeostasis has been demonstrated in the murine pituitary and adrenal gland. These cells are required for the successful adaptation of most tissues and might be responsible for morphological and functional changes typically seen in metabolic disease. External and internal stressors from the first day of life may influence the process of cell differentiation of stem and progenitor cells in the HPA axis.

The aim of the present study is to elucidate the influence of obesity and diabetes on the regulation of HPA homeostasis. We hypothesize that typical adaptational mechanisms in morphology and function of both the pituitary and the adrenal gland might be the result of activation of specific progenitor or stem cell populations. Accordingly, individual factors regulating feeding behavior such as insulin and leptin might influence these cells in proliferation and differentiation and lead to remodeling processes in order to sustain homeostasis. Therefore, we will characterize the adult progenitor and stem cell populations of the pituitary and the adrenal gland in order to study their role in metabolic disease.

In vitro, we applied insulin and leptin to murine Nestin-GFP(+) progenitor cells isolated from the anterior pituitary and the adrenal cortex and examined the influence of these hormones on proliferation and differentiation. After proliferation and differentiation of Nestin-GFP(+) adrenocortical cells in culture, we analyzed the mRNA expression of genes involved in steroidogenesis and stem cell regulation. Using Nes-CreERT^+/-;Rosa26 eYFP^+/+ mice, we were able to lineage trace Nestin(+) adrenocortical cells in which recombination was induced in vitro. Furthermore, in this study, two different in vivo mouse models were used to analyze the influence of metabolic disease on HPA axis: leptin-deficient Ob/Ob mice and high-fat diet (HFD)-induced obesity.

Insulin was shown to lead to enhanced proliferation and differentiation of both pituitary and adrenocortical progenitors. mRNA levels of various steroidogenic enzymes were upregulated in the insulin stimulated cultures of Nestin-GFP⁺ adrenocortical progenitors. In the presence of insulin, Nestin⁺ adrenocortical cells preferentially differentiated into zona glomerulosa cells accompanied with increased secretion of corticosterone and aldosterone. Likewise, descendants of Nestin⁺ anterior pituitary progenitors were positive for the CRH receptor and showed higher ACTH levels in the media under the influence of insulin. In our short metabolic stress model (8 weeks old Ob/Ob mice), we observed an activation of Nestin⁺ adrenocortical cells migrating and differentiating into steroid-producing cells. In the progenitors, no alterations were noted in our chronic metabolic stress models (10 months old Ob/Ob mice). However, hyperactivation of the HPA axis was observed in both Ob/Ob mice models with mRNA levels of steroidogenic enzymes in the adrenal gland being upregulated. Consistently, we observed adrenocortical hyperplasia due to an expansion of the zona fasciculata in 10 months old Ob/Ob mice. In the hypothalamus of Ob/Ob mice, Crh expression levels differed between the short and the more chronic metabolic stress model. The expression of the appetite-regulating genes Npy and Agrp changed in both the hypothalamus and the adrenal in Ob/Ob mice.

It is well-known that chronic stress, including release of stress hormones such as glucocorticoids, plays a major role in the development of disease states such as the metabolic syndrome. In this study, we show that this might be based on an early sensitization of progenitor-/stem cells of the HPA axis. Thus, anterior pituitary and adrenocortical progenitor cells exposed to high levels of insulin are metabolically primed to a hyperfunctional state leading to enhanced hormone production. Likewise, obese animals exhibit a hyperactive HPA axis leading to adrenocortical hyperplasia. We recently introduced the concept of stress-inducible stem cells and discussed if stress affects stem/progenitor cells through epigenetic modifications whereby they will be predisposed to adult disease. Ongoing and continuous shaping and transformation of the HPA axis through the induction of subpopulations of progenitors might then explain the influence of early life stress on mental and metabolic illness in adulthood.

Publications:

Expression of progenitor markers is associated with the functionality of a bioartificial adrenal cortex.  M. Balyura, E. Gelfgat, C. Steenblock, A. Androutsellis-Theotokis, G. Ruiz-Babot, L. Guasti, M. Werdermann, B. Ludwig, T. Bornstein, A.V. Schally, A. Brennand, S.R. Bornstein. PLoS One. 2018;13:e0194643. 

Isolation and characterization of adrenocortical progenitors involved in the adaptation to stress.  C. Steenblock, M.F. Rubin de Celis, L.F. Delgadillo Silva, V. Pawolski, A. Brennand, M. Werdermann, I. Berger, A. Santambrogio, M. Peitzsch, C.L. Andoniadou, A.V. Schally, S.R. Bornstein. Proc Natl Acad Sci U S A. 2018;115:12997-13002.

The adrenal gland in stress - Adaptation on a cellular level.  I. Berger*, M. Werdermann*, S.R. Bornstein, C. Steenblock. J Steroid Biochem Mol Biol. 2019;190:198-206.

Stress-inducible-stem cells: a new view on endocrine, metabolic and mental disease?  S.R. Bornstein, C. Steenblock, G.P. Chrousos, A.V. Schally, F. Beuschlein, G. Kline, N.P. Krone, J. Licinio, M.L. Wong, E. Ullmann, G. Ruiz-Babot, B.O. Boehm, A. Behrens, A. Brennand, A. Santambrogio, I. Berger, M. Werdermann, R. Sancho, A. Linkermann, J.W. Lenders, G. Eisenhofer, C.L. Andoniadou. Mol Psychiatry. 2019;24:2-9.

Insulin and obesity transform hypothalamic-pituitary-adrenal axis stemness and function in a hyperactive state.  M. Werdermann, I. Berger, L.D. Scriba, A. Santambrogio, P. Schlinkert, H. Brendel, H. Morawietz, A. Schedl, M. Peitzsch, A.J.F. King, C.L. Andoniadou, S.R. Bornstein, C. Steenblock. Mol Metab. 2021;43:101112.