In silicomodeling and simulation of neuroendocrine-immune modulation through adrenergic and 17β-estradiol receptors in lymphocytes show differential activation of cyclic adenosine monophosphate (cAMP)

Abstract

25Sympathetic innervation of lymphoid organs and presence of 17β-estradiol and adrenergic 26 receptors (ARs) on lymphocytes suggests that sympathetic stimulation and hormonal activation 27 may influence immune functions. Simulation of these pathways may help to understand the 28 dynamics of neuroendocrine-immune modulation at the cellular and molecular level. 29 Dose-and receptor-dependent effects of 17β-estradiol and AR sub-type-specific agonists 30 were established in vitro on lymphocytes from young male Sprague-Dawley rats and modeled in 31 silico using MATLAB Simbiology toolbox. Kinetic principles were assigned to define receptor-32 ligand dynamics and state/time plots were obtained using Ode15s solvers at different time intervals 33 for key regulatory molecules. Comparisons were drawn between in silico and in vitro data for 34 validating the constructed model with sensitivity analysis of key regulatory molecules to assess 35 their individual impacts on the dynamics of the system. Finally docking studies were conducted 36 with key ligands 17β-estradiol and norepinephrine to understand the mechanistic principles 37 underlying their interactions. 38 Adrenergic activation triggered pro-apoptotic signals while 17β-estradiol enhanced 39 survival signals showing contradictory effects as observed in vitro. Treatment of lymphocytes with 40 17β-estradiol shows ten-fold increase in survival signals concentration-dependently manner.41 cAMP activation is crucial for the activation of survival signals through p-ERK (Extracellular 42 Signal-Regulated Kinase) and p-CREB (cAMP Responsive Element Binding (protein). Inhibition 43 of p-ERK by norepinephrine and β2-AR by 17β-estradiol indicate direct influence on the down-44 stream signals altering apoptotic v/s survival signals. 3 45 Thus, the cross-talk between 17β-estradiol and adrenergic signaling pathways determines 46 lymphocyte functions in a receptor subtype-and co-activation-dependent manner in health and 47 disease. 48 1.0 Introduction 49 The neuroendocrine-immune network is a complex inter-regulatory system with wide 50 plasticity in order to maintain systemic homeostasis [1-3]. In females, the cyclic fluctuations in 51 the levels of gonadal hormones especially, 17β-estradiol affect the functioning of immune effector 52 cells by binding to specific receptors [4-7]. 53 In the periphery, in vitro and in vivo 17β-estradiol-stimulation has been shown to enhance 54 splenocyte proliferation and cytokine production through the alteration of specific signaling 55 molecules [2, 4, 8]. In the resting state, the close apposition of T-lymphocytes in direct synaptic 56 association with sympathetic noradrenergic (NA) nerve fibers that innervate the lymphoid organs 57 renders them highly responsive to norepinephrine [NE; 7, 9-13]. Since both 17β-estradiol and NE 58 mediate their effects on lymphocytes through their specific receptors, their down-stream effects 59 are dependent upon the kinetic parameters that govern receptor-ligand interactions [10, 14-16]. 60 Previous s...