Aggravated renal inflammatory responses in TRPV1 gene knockout mice subjected to DOCA-salt hypertension

Abstract

To test the hypothesis that deletion of the transient receptor potential vanilloid type 1 (TRPV1) channel exaggerates hypertension-induced renal inflammatory response, wild-type (WT) or TRPV1-null mutant (TRPV1(-/-)) mice were subjected to uninephrectomy and deoxycorticosterone acetate (DOCA)-salt treatment for 4 wk. Mean arterial pressure (MAP) determined by radiotelemetry increased in DOCA-salt-treated WT or TRPV1(-/-) mice, whereas there was no difference in MAP between two strains at the baseline or after DOCA-salt treatment. DOCA-salt treatment increased urinary excretion of albumin and 8-isoprostane in both WT and TRPV1(-/-) mice, and the increases were greater in magnitude in the latter strain. Periodic acid-Schiff and Mason's trichrome staining showed that kidneys of DOCA-salt-treated TRPV1(-/-) mice exhibited more severe glomerulosclerosis and tubulointerstitial injury compared with DOCA-salt-treated WT mice. NF-kappaB assay showed that DOCA-salt treatment increased renal activated NF-kappaB concentrations in TRPV1(-/-) mice compared with WT mice. Immunostaining and ELISA assay revealed that DOCA-salt-treated TRPV1(-/-) mice had enhanced renal infiltration of monocyte/macrophage and lymphocyte, as well as increased renal levels of proinflammatory cytokine (TNF-alpha, IL-6) and chemokine (MCP-1) compared with DOCA-salt-treated WT mice. Renal ICAM-1 but not VCAM-1 expression was also greater in DOCA-salt-treated TRPV1(-/-) than WT mice. Dexamethasone (DEXA), an immunosuppressive drug, conveyed a renoprotective effect that was greater in DOCA-salt-treated TRPV1(-/-) compared with WT mice. These data show that renal inflammation is exacerbated in DOCA-salt hypertension when TRPV1 gene is deleted and that the deterioration is ameliorated by DEXA treatment, indicating that TRPV1 may act as a potential regulator of the inflammatory process to lessen renal injury in DOCA-salt hypertension.

Fig. 1.

Graphs show the long-term telemetric recording of blood pressure and heart rate in wild-type (WT) and transient receptor potential vanilloid type 1 (TRPV1)-null mutant (TRPV1^−/−) mice with and without deoxycorticosterone acetate (DOCA)-salt treatment. Data represent daily average 24-h mean arterial pressure (A) and heart rate (B). Values are means ± SE (n = 6).

Fig. 2.

Bar graphs show the urinary albumin (A) and 8-isoprostane (B) excretion in WT and TRPV1^−/− mice, and DOCA-salt-treated WT and TRPV1^−/− mice with or without dexamethasone (DEXA) treatment. Values are means ± SE (n = 7 to 8). *P < 0.05 compared with control WT or TRPV1^−/− mice. †P < 0.05 compared with DOCA-salt-treated WT mice. #P < 0.05 compared with DOCA-salt-treated WT or TRPV1^−/− mice with DEXA treatment.

Fig. 3.

Representative light micrographs of kidney sections (A), stained with periodic acid-Schiff technique, from control WT and TRPV1^−/− mice (a and b), and DOCA-salt-treated WT and TRPV1^−/− mice with (e and f) or without (c and d) DEXA treatment. Bar graph (B) shows the average of glomerulosclerosis index. Values are means ± SE (n = 7 to 8). *P < 0.05 compared with control WT or TRPV1^−/− mice. †P < 0.05 compared with DOCA-salt-treated WT mice. #P < 0.05 compared with DOCA-salt-treated WT or TRPV1^−/− mice with DEXA treatment.

Fig. 4.

Representative light micrographs of renal cortex (A) and outer medulla (B) sections, stained with Mason's trichrome technique, from control WT and TRPV1^−/− mice (a and b), and DOCA-salt-treated WT and TRPV1^−/− mice with (e and f) or without (c and d) DEXA treatment. Bar graph (C) shows the average of tubulointerstitial injury score. Values are means ± SE (n = 7 to 8). *P < 0.05 compared with control WT or TRPV1^−/− mice. †P < 0.05 compared with DOCA-salt-treated WT mice. #P < 0.05 compared with DOCA-salt-treated WT or TRPV1^−/− mice with DEXA treatment.

Fig. 5.

Immunohistochemical staining of F4/80-positive cells (monocytes/macrophages in red) in renal cortex (A) and outer medulla (B) sections from control WT and TRPV1^−/− mice (a and b), and DOCA-salt-treated WT and TRPV1^−/− mice with (e and f) or without (c and d) DEXA treatment. Bar graph (C) shows the average of F4/80-positive cells expressed as cells per square millimeter in renal cortex and outer medulla. Values are means ± SE (n = 7 to 8). *P < 0.05 compared with control WT or TRPV1^−/− mice. †P < 0.05 compared with DOCA-salt-treated WT mice. #P < 0.05 compared with DOCA-salt-treated WT or TRPV1^−/− mice with DEXA treatment.

Fig. 6.

Immunohistochemical staining of CD3-positive cells (T lymphocytes in brown) in renal cortex (A) and outer medulla (B) sections from control WT and TRPV1^−/− mice (a and b), and DOCA-salt-treated WT and TRPV1^−/− mice with (e and f) or without (c and d) DEXA treatment. Bar graph (C) shows the average of CD3-positive cells expressed as cells per square millimeter in renal cortex and outer medulla. Values are means ± SE (n = 7 to 8). *P < 0.05 compared with control WT or TRPV1^−/− mice. †P < 0.05 compared with DOCA-salt-treated WT mice. #P < 0.05 compared with DOCA-salt-treated WT or TRPV1^−/− mice with DEXA treatment.

Fig. 7.

Bar graph shows the renal NF-κB activity in WT and TRPV1^−/− mice, and DOCA-salt-treated WT and TRPV1^−/− mice with or without DEXA treatment. Values are means ± SE (n = 7 to 8). *P < 0.05 compared with control WT or TRPV1^−/− mice. †P < 0.05 compared with DOCA-salt-treated WT mice. #P < 0.05 compared with DOCA-salt-treated WT or TRPV1^−/− mice with DEXA treatment.

Fig. 8.

Bar graphs show the renal TNF-α (A), IL-6 (B), and MCP-1 (C) in WT and TRPV1^−/− mice, and DOCA-salt-treated WT and TRPV1^−/− mice with or without DEXA treatment. Values are means ± SE (n = 7 to 8). *P < 0.05 compared with control WT or TRPV1^−/− mice. †P < 0.05 compared with DOCA-salt-treated WT mice. #P < 0.05 compared with DOCA-salt-treated WT or TRPV1^−/− mice with DEXA treatment.

Fig. 9.

Representative Western blot of ICAM-1 (A) and VCAM-1 (C) in kidneys from control WT and TRPV1^−/− mice, and WT and TRPV1^−/− mice treated with DOCA-salt. Bar graphs show the relative optical density values for ICAM-1 (B) and VCAM-1 (D) in WT and TRPV1^−/− mice with and without DOCA-salt treatment. Results were normalized by the corresponding β-actin. Values are means ± SE (n = 4 to 5). *P < 0.05 compared with control WT or TRPV1^−/− mice. †P < 0.05 compared with DOCA-salt-treated WT mice.