Susceptibility to Hypertensive Renal Disease in the Spontaneously Hypertensive Rat Is Influenced by 2 Loci Affecting Blood Pressure and Immunoglobulin Repertoire

Abstract

High blood pressure exerts its deleterious effects on health largely through acceleration of end-organ diseases. Among these, progressive loss of renal function is particularly important, not only for the direct consequences of kidney damage but also because loss of renal function is associated with amplification of other adverse cardiovascular outcomes. Genetic susceptibility to hypertension and associated end-organ disease is non-Mendelian in both humans and in a rodent model, the spontaneously hypertensive rat (SHR). Here, we report that hypertensive end-organ disease in the inbred SHR-A3 line is attributable to genetic variation in the immunoglobulin heavy chain on chromosome 6. This variation coexists with variation in a 10 Mb block on chromosome 17 that contains genetic variation in 2 genes involved in immunoglobulin Fc receptor signaling. Substitution of these genomic regions into the SHR-A3 genome from the closely related, but injury-resistant, SHR-B2 line normalizes both biomarker and histological measures of renal injury. Our findings indicate that genetic variation leads to a contribution by immune mechanisms hypertensive end-organ injury and that, in this rat model, disease is influenced by differences in germ line antibody repertoire.

Keywords: biomarkers; genetics; hypertension; immunoglobulin; proteinuria.

Figure 1

Histologically assessed glomerular and tubulo-interstitial injury scores measured in Periodic acid-Schiff-stained kidney sections and urinary albumin-creatinine ratios (UACR) and from 40 week old SHR-A3 (open), SHR-B2 (black) and congenic SHR-A3(chr17 SHR-B2) (gray) animals (SHR-A3, SHR-A3(chr17 SHR-B2), SHR-B2, n = 8, 12, 21 respectively). NS = no significant difference, * = p<0.05 and *** = p<0.001 (ANOVA, Scheffé test).

Figure 2

Serum IgG subclass levels were assessed by ELISA in 30 week old SHR-A3, SHR-B2 and SHR-A3(IgH SHR-B2), n = 6 per group. Significant differences in IgG1, IgG2b and IgG2c in SHR-A3 versus SHR-B2 were observed. In the congenic line, transfer of the SHR-B2 IgH segment into SHR-A3 resulted in serum IgG subclass levels that closely resembled the donor (SHR-B2) levels for IgG2b and IgG2c. For IgG2a, no effect of congenic transfer was predicted based on prior mapping, though a reduction was observed in the congenic line. For IgG1, the congenic levels were intermediate between the donor and recipient levels and not significantly different from either (*** p<0.001, ** p<0.01, *, p<0.05, NS not significantly different).

Figure 3

Histologically assessed glomerular and tubulo-interstitial injury scores and urinary albumin-creatinine ratios (UACR) and from 40 week old SHR-A3 (open), SHR-B2 (black) and the congenic SHR-A3(IgH SHR-B2) (gray) lines, n = 8, 19, 21 respectively. Glomerular and tubulo-interstitial injury were both significantly reduced in the congenic line, compared to SHR-A3, UACR was not different. NS = no significant difference, * = p<0.05 and *** = p<0.001 (ANOVA, Scheffé test)

Figure 4

Histologically assessed glomerular and tubulo-interstitial injury and urinary albumin-creatinine ratios (UACR) and from 40 week old SHR-A3 (open), SHR-B2 (black) and the congenic SHR-A3(IgH, chr17 SHR-B2) double congenic line (hatched) n = 8, 20, 21 respectively. Glomerular and tubulo-interstitial injury scores were not significantly different in the congenic line compared to SHR-B2, however UACR was different from SHR-B2, but not from SHR-A3. NS = no significant difference, * = p<0.05 and *** = p<0.001 (ANOVA, Scheffé test)

Figure 5

Urinary biomarker levels normalized to urine creatinine in 30 week old SHR-A3 (open), SHR-B2 (black), the SHR-A3(chr17 SHR-B2) congenic line (light gray), the SHR-A3(IgH SHR-B2) congenic line (dark gray) and the double congenic SHR-A3(IgH, chr17 SHR-B2) line (hatched), n = 8 per group. Although presented in a single figure for clarity, the hypotheses tested by comparing each of the congenic lines with the two parental strains are independent and statistical significance testing (ANOVA, Scheffé test) reflects this. Comparing SHR-A3(IgH SHR-B2) to its parental strains: NGAL; SHR-A3 vs SHR-B2 p = 0.03,SHR-A3 vs SHR-A3(IgH SHR-B2) p = NS, SHR-A3(IgH SHR-B2) vs SHR-B2 p = NS: OPN; SHR-A3 vs SHR-B2 p = 0.001, SHR-A3 vs SHR-A3(IgH SHR-B2) p = 0.02, SHR-A3(IgH SHR-B2) vs SHR-B2 p = NS: Kim1; SHR-A3 vs SHR-B2 p = 0.001, SHR-A3 vs SHR-A3(IgH SHR-B2) p = 0.03, SHR-A3(IgH SHR-B2) vs SHR-B2 p = NS. Comparing SHR-A3(chr17 SHR-B2) to its parental strains: NGAL; SHR-A3 vs SHR-B2 p = 0.01,SHR-A3 vs SHR-A3(chr17 SHR-B2) p = 0.03, SHR-A3(chr17 SHR-B2) vs SHR-B2 p = NS: OPN; SHR-A3 vs SHR-B2 p = 0.002,SHR-A3 vs SHR-A3(chr17 SHR-B2) p = 0.04, SHR-A3(chr17 SHR-B2) vs SHR-B2 p = NS: Kim1; SHR-A3 vs SHR-B2 p = 0.002, SHR-A3 vs SHR-A3(chr17 SHR-B2) p = NS, SHR-A3(chr17 SHR-B2) vs SHR-B2 p = 0.05. Comparing SHR-A3(IgH, chr17 SHR-B2) to its parental strains: NGAL; SHR-A3 vs SHR-B2 p = 0.01, SHR-A3 vs SHR-A3(IgH, chr17 SHR-B2) p = 0.01, SHR-A3(IgH, chr17 SHR-B2) vs SHR-B2 p = NS: OPN; SHR-A3 vs SHR-B2 p = 0.0003,SHR-A3 vs SHR-A3(IgH, chr17 SHR-B2) p = 0.0003, SHR-A3(IgH, chr17 SHR-B2) vs SHR-B2 p = NS: Kim1; SHR-A3 vs SHR-B2 p = 0.0003, SHR-A3 vs SHR-A3(IgH, chr17 SHR-B2) p = 0.0005, SHR-A3(IgH, chr17 SHR-B2) vs SHR-B2 p = NS.