Abstract 001: Sympathetic Innervation Promotes Bone Marrow Homing of Hypertension-specific CD8 + Effector Memory T Cells

Abstract

We have recently identified a critical role of hypertension-specific effector memory T lymphocytes (T EM cells) in the blood pressure elevation and renal dysfunction caused by repeated hypertensive stimuli. Formed during an initial immune challenge, T EM cells reside in the bone marrow (BM) in a quiescent state for prolonged periods, and can be reactivated upon re-exposure to the hypertensive stimulus. Hypertension is associated with increased sympathetic outflow. We therefore hypothesized that sympathetic nerves regulate accumulation and reactivation of hypertension-specific T EM cells in the BM. We performed unilateral superior cervical ganglionectomy (SCGx) in wild-type C57BL/6 mice, causing selectively sympathectomy of the forelimb on the surgical side. After recovery, mice received Ang II infusion for two weeks. To determine the changes of T cells in the BM that were specific to hypertension, 5х10 6 BM cells were isolated from either the SCGx or control limbs, loaded with proliferation marker CFSE, and co-cultured with 0.5х10 6 splenic dendritic cells isolated from another Ang II-infused mouse. We found 30% less CD8 + T cell proliferation in the SCGx BM compared to control side (1.8±0.1 vs. 2.6±0.3х10 4 ), but no difference in CD4 + T cells. To further study the effect of sympathetic nerves on BM T cell homing, 1х10 7 pan T cells were isolated from CD45.2 + wild-type mice after Ang II infusion and adoptively transferred to CD45.1 mice that had previously undergone unilateral SCGx. Flow cytometry indicated that 7 days after transfer, 25% fewer CD8 + T EM cells from the hypertensive donors homed to the SCGx BM compared to the innervated BM (27.8±2.6 vs. 20.8±2.5 per 10 3 total BM cells). This effect was specific for hypertension as homing of OT-I T EM cells, which are responsive to ovalbumin, was not influenced by sympathectomy. Further adoptive transfer studies using mice lacking beta 2 adrenergic receptors (β2AR) indicate that β2AR in the bone marrow niche, rather than T cell β2AR is critical for T EM cell homing. These data define a novel role of sympathetic nerves in regulation of memory T cell trafficking, and this likely contributes to the predisposition to hypertension and end-organ damage for prolonged periods following an initial episode of hypertension.