Identification of a Novel T‐lymphocyte Inflammatory Protein in Psychological Stress‐ Induced Hypertension

Abstract

Post‐traumatic stress disorder (PTSD) is a psychiatric condition characterized by hyperarousal, anxiety, anhedonia, and depression. While the behavioral manifestations are often the focus of this disease, PTSD also alters physiological processes leading to elevated sympathetic tone and norepinephrine (NE) outflow, pronounced inflammation, and a >50% increased risk in developing co‐morbid cardiovascular diseases like hypertension. Our laboratory previously reported that exposure to NE can modulate levels of T‐lymphocyte pro‐inflammatory cytokines, and understanding that hypertension is regulated in part due to inflammation, we posited a connection between the autonomic nervous, immune, and cardiovascular systems in PTSD patients. We hypothesized that psychological stress‐induced sympathoexcitation leads to increased pro‐inflammatory cytokine production from T‐lymphocytes, which impacts the development of hypertension. Utilizing a mouse‐model of PTSD‐like psychological trauma, lymphatic sympathoexcitation was confirmed by a 2.5 fold increase in NE and 4.1 fold increase in tyrosine hydroxylase content in spleens from stressed animals (p<0.001). This increased sympathetic tone correlated with elevated pro‐inflammatory cytokines IL‐17A, IL‐6, and IL‐2 (+4.4, +3.1, and +3.0 fold, respectively, p<0.01) both in circulation and also specifically within splenic T‐lymphocytes. Examination of hemodynamics in the stressed mice elucidated a stable increase in resting mean arterial pressure (+19.5 mmHg, p<0.05) over the stress‐induction period with an even greater (+39.8 mmHg, p<0.01) rise after stress context re‐exposure compared to control animals. To investigate the causal contribution of T‐lymphocytes in driving this hypertensive response, recombination activating gene 2 (Rag2) knock‐out animals, devoid of mature lymphocytes, were utilized. Rag2 knock‐out mice showed no changes in pro‐inflammatory cytokines, a 75% decrease in splenic TH levels (p<0.01), and a blunted blood pressure response upon context re‐exposure (+8.8 mmHg, p<0.01). Single cell RNAseq analysis of T‐lymphocytes from stressed wild‐type animals demonstrated a significant increase (p=8.6×10−19) in calprotectin (S100a8 and S100a9) mRNA levels compared to control. Calprotectin is both an intracellular and extracellular protein involved in many inflammatory processes, but has been thought to be granulocyte‐specific making its detection in T‐lymphocytes highly unexpected. We confirmed 40 and 30‐fold increases in S100a8 and S100a9 mRNA, respectively, in purified T‐lymphocytes from stressed animals by qRT‐PCR (p<0.01). Additionally, a 3‐fold increase (p<0.001) in levels of calprotectin protein was observed in circulation of stressed animals. Last, we identified an approximate 2‐fold increase (p<0.05) in calprotectin protein levels in circulation from human patients with PTSD with comorbid hypertension compared to PTSD alone. Taken together, our data suggest a new role for T‐lymphocytes in the regulation of stress‐induced inflammation and hypertension, and present an undescribed protein target for future investigation and potential therapeutic intervention.Support or Funding InformationNIH R00HL123471This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.