A role for angiotensin II type 1 receptors on bone marrow-derived cells in the pathogenesis of angiotensin II-dependent hypertension

Abstract

Activation of type 1 angiotensin (AT(1)) receptors causes hypertension, leading to progressive kidney injury. AT(1) receptors are expressed on immune cells, and previous studies have identified a role for immune cells in angiotensin II-dependent hypertension. We, therefore, examined the role of AT(1) receptors on immune cells in the pathogenesis of hypertension by generating bone marrow chimeras with wild-type donors or donors lacking AT(1A) receptors (BMKO). The 2 groups had virtually identical blood pressures at baseline, suggesting that AT(1) receptors on immune cells do not make a unique contribution to the determination of baseline blood pressure. By contrast, in response to chronic angiotensin II infusion, the BMKOs had an augmented hypertensive response, suggesting a protective effect of AT(1) receptors on immune cells with respect to blood pressure elevation. The BMKOs had 50% more albuminuria after 4 weeks of angiotensin II-dependent hypertension. Angiotensin II-induced pathological injury to the kidney was similar in the experimental groups. However, there was exaggerated renal expression of the macrophage chemokine monocyte chemoattractant protein 1 in the BMKO group, leading to persistent accumulation of macrophages in the kidney. This enhanced mononuclear cell infiltration into the BMKO kidneys was associated with exaggerated renal expression of the vasoactive mediators interleukin-1beta and interleukin-6. Thus, in angiotensin II-induced hypertension, bone marrow-derived AT(1) receptors limited mononuclear cell accumulation in the kidney and mitigated the chronic hypertensive response, possibly through the regulation of vasoactive cytokines.

Figure 1

Recipients of bone marrow lacking AT_1A receptors have an augmented chronic hypertensive response to Ang II. Mean arterial blood pressures measured by radiotelemetry in the experimental groups at baseline (“pre”) and during 3 weeks of Ang II infusion. BMWT, circles. BMKO, triangles. n = 11 per group.

Figure 2

Deficiency of AT_1A receptors on bone marrow cells leads to increased albuminuria after angiotensin II infusion. Urinary albumin excretion (micrograms per milligram of creatinine) in the experimental groups after 25 days of Ang II or saline infusion. *P<0.0002 vs BMWT-saline. †P<0.0001 vs BMKO-saline, P=0.003 vs BMWT-Ang.

Figure 3

AT₁ receptor-deficient bone marrow chimeras have enhanced renal accumulation of macrophages in Ang II–dependent hypertension. A, Representative kidney section from BMWT-saline group showing minimal injury (×10). B, Representative kidney section from BMWT-Ang group showing mild glomerulosclerosis, mononuclear cell infiltrates, and rare fibrosis. C through F, Representative kidney sections from BMWT-saline (C), BMKO-saline (D), BMWT-Ang (E), and BMKO-Ang (F) groups stained brown for macrophages (×20). G, Proportion of high-powered (×40) fields containing ≥5 F4/80⁺ macrophages. *P<0.007 vs BMWT-saline. †P<0.03 vs BMWT-Ang.

Figure 4

Determinants of macrophage migration in the experimental groups. A, Renal MCP-1 expression measured by realtime PCR in the experimental groups after saline or Ang II infusion. *P=0.05 vs BMWT-saline. †P=0.02 vs BMWT-saline. ‡P=0.02 vs BMWT-Ang. B, Freshly isolated peritoneal WT or Agtr1a^−/− macrophages were cultured in the upper chamber of a chemotaxis well with vehicle (black) or MCP-1 plus Ang II added to the lower chamber in the absence (white) or presence (gray) of AT₂ receptor antagonist PD123319. MCP-1 with Ang II induced significant chemotaxis that was nearly abrogated by PD123319 compound in both groups. N=6 per group. *P=0.001 vs WT cells alone. †P<0.004 vs WT MCP-1/Ang II. ‡P<0.002 vs Agtr1a^−/− cells alone. P value not significant vs WT MCP-1/Ang II. #P=0.04 vs Agtr1a^−/− MCP-1/Ang II.

Figure 5

AT₁ receptors on immune cells influence renal mRNA expression for inflammatory mediators. Relative expression measured by real-time PCR for (A) TNF-α. *P<0.07 vs BMWT-saline. †P<0.03 vs BMKO-saline. B, IL-1β. *P=0.02 vs BMKO-saline, P=0.05 vs BMWT-Ang. C, TGF-β. *P=0.05 vs BMWT-saline; †P=0.02 vs BMWT-Ang. mRNA expression normalized to BMWT-saline group in each panel.