Estrogen Receptors Differentially Regulate the Overall Contractility of Human Airway Smooth Muscle
Authors: Bhallamudi Sangeeta , Ambhore Nilesh Sudhakar , Saladi Swetha , Pabelick Christina M. , Prakash Y.S. , Sathish Venkatachalem 
Published: April 2020

Purpose

Epidemiological evidences suggest higher incidence and severity of asthma in pre‐menopausal women and aging men, indicating the role of sex steroids, especially estrogen. Our recent studies demonstrated that airway smooth muscle (ASM) cells from both male and female expresses estrogen receptors (ERα and β) and these receptors differentially regulate intracellular calcium ([Ca2+]i) which is a key role player in contraction. The degree of force for contraction can also be altered in a Ca2+‐independent manner via RhoA. Both Ca2+‐dependent and Ca2+‐independent pathways in ASM thus together contribute towards the airway contractility. In this study, we hypothesized that the ERs differentially regulate cyclic adenosine monophosphate (cAMP) and RhoA mechanisms, thereby affecting the overall contractility of human ASM cells.

Methods

Asthmatic and non‐asthmatic primary human ASM cells (isolated from lung tissue, Mayo Clinic, IRB‐approved) were seeded and grown to 70% confluence. After serum‐deprivation, cells were exposed to 1nM 17β‐estradiol (E2), 10nM PPT (ERα agonist) or WAY (ERβ agonist) for 24hr. IBMX (10μM) was used as phosphodiesterase inhibitor and Isoproterol (100nM for 10min) served as a positive control group for estimation of cAMP. In parallel studies, phosphorylation of myosin light chain (MLC20) and myosin phosphatase targeting subunit‐1 (MYPT1) was assessed through Western analyses. Activated RhoA and cAMP measurements were done through ELISA kits. Cell contraction was accessed through traction force microscopy (TFM) using softgel plates coated with collagen and fluorescent beads. Upon treatments, phase‐contrast and fluorescent images were captured before, during and after 10μM histamine exposure and net traction force was calculated using advanced software.

Results

Prolonged (24h) activation of ERβ significantly increased the baseline cAMP levels whereas ERα activation decreased it. This effect was more profound in asthmatic ASM cells compared to non‐asthmatics. Furthermore, ERβ activation lowered the active RhoA levels in non‐asthmatic human ASM cells. The phosphorylation of MLC20 and MYPT1 was significantly attenuated with ERβ activation compared to vehicle. TFM studies demonstrated reduced traction force in non‐asthmatic ASM cells treated with ERβ agonist compared to the vehicle, whereas ERα activation did not show any significant changes.

Conclusion

Our findings highlight the crucial role of divergent ER signaling in regulating Ca2+‐dependent and Ca2+‐independent pathways, which together govern the contractile function of ASM. Particularly, ERβ activation (and not ERα) mediates ASM relaxation by increasing the cAMP, reducing active RhoA and decreasing phosphorylation of MLC20/MYPT1. Thus, ERβ activation might serve as a novel target to manage the increased ASM contractility in asthma.

Support or Funding Information

Acknowledgement

Supported by NIH grants R01‐HL0123494 (Venkatachalem), R01‐HL 088029 (Prakash) and R01‐HL142061 (Pabelick, Prakash).