Estrogen differentially regulates the expression of tyrosine hydroxylase and nerve growth factor through free radical generation in the thymus and mesenteric lymph nodes of middle‐aged ovariectomized female Sprague–Dawley rats

Abstract

Objective Sympathetic neuronal activity in the thymus and lymph nodes is differentially regulated during reproductive aging. The aim was to investigate the role of estrogen on sympathetic neuronal expression in the thymus and mesenteric lymph nodes of early middle-aged ovariectomized female rats implanted with 17b-estradiol pellets. Methods 17b-Estradiol pellets (0.6 and 300) were implanted subcutaneously in ovariectomized middle-aged female Sprague-Dawley rats (n = 8/group) for a period of 30 days. At the end of the treatment period, the thymus and mesenteric lymph nodes were isolated and analyzed for the expression of tyrosine hydroxylase, nerve growth factor, and p-ERK, p-CREB and p-Akt. Results The age-related increase in tyrosine hydroxylase expression in the thymus was abrogated by ovariectomy, while estrogen suppressed it further and nerve growth factor expression was altered based on the dose of estrogen. In contrast, estrogen increased tyrosine hydroxylase and nerve growth factor expression in the mesenteric lymph nodes. Estrogen enhanced p-ERK/ total ERK, CREB/total CREB and p-Akt/total Akt expression in a dose-dependent manner. Free radical generation was augmented by estrogen in the thymus alone. Conclusions These results suggest that estrogen differentially influences sympathetic neuronal activity in the primary and secondary lymphoid organs to influence immunity.

Neuroimmunomodulation by estrogen in health and disease

“…The neuroprotective role of estrogen has been well established and yet, the perimenopausal estrogen surge in rodents has been shown to be implicated in the loss of sympathetic NA innervation of lymphoid organs leading to disruption in neuroendocrine-immune homeostasis in the periphery [22] , [23] . Treatment of ovariectomised middle-aged Sprague-Dawley (SD) rats with estrogen [0.6 µg and 300 µg timed-sustained release (SR) pellets/30 days] significantly decreased the expression of p-TH in the mesenteric lymph nodes [24] . The onset of menopause is characterised by a dramatic decline in circulating levels of estrogen leading to a hypoestrogenic state that have lasting implications on the reproductive and non-reproductive functions of the hormone ranging from loss of rhythmicity in neurotransmitter dynamics in the brain to a decline in peripheral immune responses [25] , [26] .…”

Regulation of Immunity by Estrogen Through Sympathetic Nervous System in Aging

“…[24] In an attempt to understand the role of estrogen on neuralimmune interactions, we performed a study in which ovariectomized (OVX) early middle-aged animals (8-to 9-mo-old female Sprague-Dawley rats) were treated with two doses of E2 (30-day implantation of 0.6 µg or 300 µg pellets of 17β-estradiol) and its effects investigated on various areas of brain [frontal cortex (FC), striatum (STR), medial basal hypothalamus (MBH), and hippocampus (HP)], thymus, spleen, and lymph nodes. [13][14][15][16] Brain: Treatment with E2 augmented p-tyrosine hydroxylase expression in the frontal cortex and hippocampus, decreased NF-κB expression in the frontal cortex and striatum, and enhanced cholinergic neuronal activity in hippocampus and striatum accompanied by estrogen-induced reversal of age-and OVX-related decline in intracellular signaling molecules (p-ERK, p-CREB, and p-Akt). [15] Also, there was an increase in the activities of antioxidant enzymes [superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx), glutathione-S-transferase (GST)] and nitric oxide (NO) production, and a simultaneous decline in lipid peroxidation.…”

“…Thymus: Estrogen treatment inhibited the parathormon expression in the thymus and increased the expression of p-ERK, p-CREB, and p-Akt indicating that E2 causes neurodegeneration in the thymus possibly through increased production of free radicals. [16] These effects may accentuate E2-induced inhibition of the early thymic progenitor cell population and arrest T cell maturation through ERα and Fas/FasL pathway to create inflammatory environment. [26,27] Spleen: Administration of E2 altered tyrosine hydroxylase expression and immune responses in a dose-dependent manner in the spleen: low dose E2 suppressed IFN-γ production, increased Con A-induced lymphoproliferation, IL-2 production, expression of intracellular signaling molecules (p-ERK, p-CREB, and p-Akt), antioxidant enzyme activities (SOD, CAT, and GST), and NO production while high dose E2 inhibited Con A-induced lymphoproliferation but enhanced the expression of p-TH, NGF, intracellular signaling molecules (p-ERK and p-CREB), and activities of antioxidant enzymes (SOD and GST).…”

“…[14] However, similar treatment with E2 had different effects in MLN where it enhanced the activities of antioxidant enzymes without an increase in free radical generation suggesting that estrogen exerts neuroprotective effects on sympathetic NA activity in MLN. [16] The differential effect of estrogen on these two lymph nodes may be due to possible differences in stromal cells that may regulate trafficking of immune cells and immune molecules through the lymph nodes.…”

“…[9][10][11] Published studies from our laboratory form the basis for this short review where we discuss the role of E2 modulating neural-immune interactions in the brain areas (frontal cortex, striatum, medial basal hypothalamus, and hippocampus) and lymphoid organs (thymus, spleen, and lymph nodes) of early middle-aged rats mediated through the antioxidant enzymes, growth factors, and intracellular signaling molecules and transcription factors (ERK, CREB, Akt, mTOR, and NF-κB). [13][14][15][16]…”