Abstract 167: Mapping of Chromosome 2 Regions Linked to Vascular Inflammation Using Congenic Rats

Abstract

Background: Immune cells have been implicated in hypertension and vascular inflammation. We demonstrated that chromosome 2 modulates immune responses in genetic hypertension via T regulatory lymphocytes (Treg). Introgression of chromosome 2 from normotensive Brown Norway (BN) rats into hypertensive Dahl salt sensitive (SS) background (consomic SB2) reduced vascular inflammation and restored Treg function. We hypothesized that the BN chromosome 2 contains genes that reduce vascular inflammation, which could be mapped using congenic rats containing portions of BN chromosome 2 on the SS background.

Methods: Twelve-to-13 week old male BN, SS, SB2, congenic (SB)A, SBB and SBE rats fed normal salt diet were studied. Systolic blood pressure (SBP) was measured by telemetry. Spleen Treg (CD4⁺CD25^hi) and CD4⁺CD25^- T lymphocytes were isolated and characterized by fluorescence-activated cell sorting (FACS) and cultured. Transforming growth factor (TGF)-β, tumor necrosis factor (TNF)-α, interleukin (IL)-10, IL-17 and IL-6 secreted by 10⁵ cells in culture media was measured by microbead multiplex immunoassays. Aortic collagen content was determined by Sirius red staining.

Results: SS, SB2 and SBE exhibited 20 mmHg higher SBP compared to BN, SBA, and SBB (P<0.05). The % of CD4⁺CD25^- was higher in SS, SB2 and SBE (∼16 %) compared to BN, SBA and SBB (∼12%, P<0.05). The % of Treg was lower in SBA (2%) compared to SS and SB2 (3%, P<0.05). CD4⁺CD25^- secretion of TNF-α, IFN-γ and IL-6 was always lower in SS and SBB (≤141, 1428 and 13 pg/10⁵ cells, respectively, P<0.05), and consistently unchanged in SB2 and SBE (∼320, 22350 and 50 pg/10⁵ cells, respectively) compared to BN (458, 3552 and 57 pg/10⁵ cells, respectively). Treg IL-10 and IL-17 production was increased in SB2 (9597 pg/10⁵ cells), and SS and SB2 (>90 pg/10⁵ cells), respectively (P<0.05) and unchanged in congenic rats (∼2540 and 23 pg/10⁵ cells, respectively), compared to BN (2497 and 9 pg/10⁵ cells). Aortic collagen was increased 3-fold in SS, 1.7-fold in SB2 and SBB (P<0.05) and unchanged in SBA and SBE compared to BN.

Conclusion: These results suggest that some of the genes that regulate vascular inflammatory responses are contained within the fragment of chromosome 2 from Brown-Norway rats present in congenic SBE rats.