Effect of Losartan on Acute Expression of Renin‐Angiotensin System Genes in the Spinal Cord and Peripheral T‐Cell CD11a Expression following Spinal Cord Injury in Rats

Abstract

BackgroundSpinal cord injury (SCI) causes primary trauma followed by immune‐mediated secondary expansion. Thus, immune modulation may mitigate secondary injury and improve recovery post‐SCI. Previous data from our laboratory indicated that treatment with losartan (an angiotensin II type1 receptor blocker) improved recovery, and decreased T‐cell infiltration into the injured rat spinal cord at 7 through 28 days post injury (DPI), however a mechanism for these effects was not readily apparent, as spinal cord expression of renin‐angiotensin system (RAS) genes was greatly reduced. Based on these findings, we hypothesized two mechanisms for losartan's effects post‐SCI: 1) Acute RAS gene increases in injury margins could increase T‐cell recruitment; and 2) Peripheral RAS inhibition could alter T‐cell CD11a expression and spinal cord infiltration. Accordingly, our objectives were to 1) examine RAS gene expression, and 2) T‐cell CD11a expression in peripheral blood, 1 and 3 DPI in losartan‐treated rats.MethodsA moderate, lateral compression SCI was induced at T8 in rats. Injured rats were treated with losartan or vehicle i.p. immediately after injury and every 24h thereafter for 1 or 3 DPI. Uninjured rats were used as SCI controls. At sacrifice, rats were anesthetized, perfused with saline, and spinal cord and blood were harvested. The spinal cord was segmented into three 3‐mm sections (rostral, injury epicenter, and caudal) and processed for qRT‐PCR. Genes assayed were angiotensinogen (agt), angiotensin converting enzyme (Ace1), and the angiotensin II type 1‐ (Agtr1a) and type 2‐ (Agtr2) receptors. Blood was assayed by flow cytometry for CD3, CD8, and CD11a.ResultsSimilar to our previous findings at 7–28 DPI, RAS gene expression at 1 DPI was lowered significantly by injury compared to uninjured animals. The effect was maximal at the injury epicenter and intermediate in the rostral and caudal segments. There was no significant effect of losartan. At 3 DPI, Agt, Ace1 and Agtr2, were likewise downregulated. However Agtr1a returned to nearly uninjured levels at the epicenter only, while rostral and caudal Agtr1a mRNA was unchanged from 1 to 3 DPI. In peripheral blood, the percentage of CD11a ‘high’ CD3+/CD8+ lymphocytes was highly variable following SCI. At 3 DPI losartan lowered mean CD11a expression about two fold, but high variability rendered the result not statistically significant.ConclusionsThe increase in Agtr1a expression from 1 to 3 DPI at the injury epicenter suggests infiltration of a cell type expressing AT1R. This time point corresponds to the infiltration of T‐cells which are known to express Agtr1a. Inhibition of AT1R by losartan on these cells could explain some of the mechanism for losartan's effects on T‐cell infiltration and recovery from SCI. Peripheral CD11a expression was highly variable in response to SCI, however a losartan‐induced reduction in CD11a expression at 3 DPI, when T‐cells are known to be infiltrating the injured spinal cord, suggests a possible mechanism for beneficial effects of losartan in the injured spinal cord.Support or Funding InformationFunded by Midwestern University.