Rapid Progesterone Actions on Thymulin-Secreting Epithelial Cells Cultured from Rat Thymus

Abstract

Many soluble factors of neural, endocrine, paracrine and autocrine origin are present in the thymus and modulate its function. Long-term effects of sex steroids have been documented for thymocytes and cells of the thymic microenvironment. In this report we examine rapid actions of progesterone upon aspects of epithelial cell physiology. Progesterone (0.1–10 µM) was applied to cultured thymulin-secreting thymic epithelial cells (TS-TEC) and changes in transmembrane potential, transmembrane current, intracellular calcium levels and thymulin secretion were assessed. Rapid changes in electrophysiology and intracellular calcium provide evidence for a membrane-bound progesterone receptor in these cells, in addition to classical cytoplasmic receptors. Application of progesterone to TS-TEC caused electrophysiological changes in 56% of cells (n = 40), activating an inward current (–24 ± 9 pA at 1 µM, n = 7, p < 0.02) and dose-dependent depolarization (7.1 ± 1.8 mV at 1 µM, n = 19, p < 0.01). Intracellular calcium levels, monitored by the ratiometric fluorescent calcium indicator fura-2, increased within seconds of progesterone (1 µM) application. Progesterone (1 µM) increased thymulin levels in supernatant, as measured by ELISA, above the levels in the preapplication period (142 ± 16% of the preapplication period, n = 3, p < 0.02). This effect was reduced in the presence of cobalt chloride which blocks voltage-dependent calcium channels. In addition, TS-TEC in culture were immunoreactive to antibody AG7. This antibody was raised to a membrane-bound antigen involved in calcium influx subsequent to progesterone binding in sperm. Thus we suggest that progesterone acts upon many aspects of TS-TEC physiology through both cytoplasmic and membrane-bound receptors.

The Immunoendocrine Thymus as a Pacemaker of Lifespan

“…In thymus culture, progesterone increases the thymulin level [92]. Thymulin and thymosin alpha 1 production are inhibited by sex hormone treatments [93].…”

Nongenomic Steroid Action: Controversies, Questions, and Answers

“…The steroid (1 M) has also been described to rapidly increase and induce membrane depolarizations and inward currents in thymic epithelial cells (209). In addition, similar concentrations of the steroid cause an immediate rise in [Ca 2ϩ ] i in a murine Leydig tumor cell line (mLTC-1) which seems to be devoid of PR (129).…”

Ion Channel Regulation by Sex Steroid Hormones and Vitamin D in Cancer: A Potential Opportunity for Cancer Diagnosis and Therapy

“…Furthermore, a comparison of lung homogenates from female rats in pro-estrous and di-estrous phases revealed that the highest number of ENaC channels expressed in the cell membrane parallels the highest level of circulating estradiol (Matalon et al, 2015). Head et al (1999) observed that progesterone rapidly activates an inward current and increases the intracellular calcium concentration in thymulin-secreting epithelial cells from rat thymus. Because of the rapid response to progesterone, such effect had likely been mediated by a nontranscriptional pathway requiring the activation of a second messenger.…”

“…(B) Non-transcriptional pathways primarily involve the binding of the SH to a GPCR triggering second messenger pathways which may activate proteins targeting to ion channels. Alternatively, SH may bind to ion channels like TRPM8 and CatSper modulating its gating properties and enhancing calcium influx (Head et al, 1999;Asuthkar et al, 2015;Grolez et al, 2019). Changes in ion channel expression or activity produced by SH may in turn affect some cancer-associated processes, including cancer cell proliferation, migration, and invasion.…”