Mouse chromosome 2 harbors genetic determinants of resistance to podocyte injury and renal tubulointerstitial fibrosis

Abstract

Background: Tensin2 deficiency results in alterations in podocytes and subsequent glomerular and tubulointerstitial injuries. However, this pathology is critically dependent on genetic background. While the Tensin2-deficient podocytes of resistant murine strains, including C57BL/6J mice, remain almost intact, susceptible murine strains with Tensin2 deficency, including ICGN mice, develop chronic kidney disease following alterations in the podocyte foot processes. In a previous study, genome-wide linkage analysis was utilized to identify the quantitative trait loci associated with the disease phenotypes on mouse chromosome 2. This study investigated the disease phenotypes of chromosome 2 consomic and subcongenic strains.

Results: ICGN consomic mice introgressed with chromosome 2 from the C57BL/6J mouse were generated and found to exhibit milder renal failure than that in ICGN mice. We developed 6 subcongenic strains that carry C57BL/6J-derived chromosomal segments from the consomic strain. One showed significantly milder albuminuria, another showed significantly milder tubulointerstitial injury, and the both showed significantly milder glomerular injury.

Conclusions: These data indicate that mouse chromosome 2 harbors two major genes associated with the severities of nephropathy induced by Tensin2 deficiency. The proximal region on chromosome 2 contributes to the resistance to tubulointerstitial fibrosis. In contrast, the distal region on chromosome 2 contributes to the resistance to podocyte injury. This study would be helpful to discover the biological mechanism underlying the renal injury, and may lead to the identification of therapeutic targets.

Keywords: Albuminuria; Chronic kidney disease; Renal fibrosis; Tensin2.

Fig. 1

Measurements of blood and urine. a Hematologic parameters at 16 weeks of age. The levels of Hb and Ht in ICGN-Chr 2^B6 mice and ICGN-Tns2 ^WT mice were normal. With regard to BUN, no significant difference was observed between ICGN and ICGN-Chr 2^B6 mice, with some ICGN mice but no ICGN-Chr 2^B6 mice showing abnormal BUN levels. b Urinary albumin excretion. Albuminuria was already observed at 4 weeks after birth in ICGN and ICGN-Chr 2^B6 mice. Asterisks indicate P-values for Dunnett’s multiple comparison test, ** <0.01 and * <0.05 vs. ICGN mice (a), or ICGN-Chr 2^B6 mice at the same time point (b) n.s., not significant. Error bars represent standard error. Eleven ICGN mice, four ICGN-Chr 2^B6 mice and three ICGN-Tns2 ^WT mice were analyzed

Fig. 2

Histological analyses of PAS-stained renal sections from 16-week-old mice. a Representative glomerular and cortical sections. ICGN: entire expansion of the mesangial matrix and vascular dilations (score 5), massive tubular dilations with urinary casts and cell infiltrations. ICGN-Chr 2^B6: partial expansion of the mesangial matrix and vascular stenoses (score 3). ICGN-Tns2 ^WT: nearly normal (upper, score 0), partial expansion of the mesangial matrix and vascular wall thickening (lower, score 2). b The mean ratio of the glomerular injury scores each sample. c Glomerular injury index and tubular injury index. Asterisks indicate P-values for Dunn’s multiple comparison test, ** <0.01 and * <0.05 vs. ICGN mice. Error bars represent standard error. Eleven ICGN mice, four ICGN-Chr 2^B6 mice and three ICGN-Tns2 ^WT mice were analyzed

Fig. 3

Ultrastructure of the glomeruli at 16 weeks of age. In ICGN mice (a), high-level effacement of the podocyte foot processes, high-level thickening of the GBM and swelling of the podocytes (Pod) were observed. In ICGN-Chr 2^B6 mice (b), normal GBM and foot processes (arrow) as well as thickening of the GBM (asterisk) and effacement of the foot processes (arrowhead) were observed with a much milder phenotype than that of ICGN mice. In ICGN-Tns2 ^WT mice (c), the glomeruli were nearly normal, but some part of the foot processes and the GBM was abnormal. Cap, capillary

Fig. 4

Chromosome 2 genotypes and phenotypic summary of the congenic strains. The white and black bars indicate the genomic region from ICGN and B6 mice, respectively. The shaded bar shows an unclear genomic region in which recombination occurred. If a phenotypic severity was significantly alleviated by genetic recombination compared to that of ICGN mice (see Fig. 5 and Additional file 1: Figure S2), it is defined as resistant (R). If not, it is defined as susceptible (S). Tns2 ^nph-induced tubulointerstitial fibrosis related locus, Ttir, is located in rs33151033-D2Mit378 (49.5–68.8 Mb). Tns2 ^nph-induced podocyte injury related locus, Tpir, is located in D2Mit102-D2Mit409 (114.1–158.5 Mb)

Fig. 5

Urinary albumin excretion, glomerular index and tubular index of the congenic strains. ICGN-Chr 2^B6 and ICGN data are identical to Figs. 1b and 2. Statistical analysis was performed for ICGN and all subcongenic strains. Dunn’s and Dunnett’s multiple comparison test were used for statistical analyses of glomerular and tubular injury indexes, and urinary albumin excretion, respectively. Asterisks indicate P-values, *** <0.001, ** <0.01 and * <0.05 vs ICGN mice. n.s., no significant differences compared with ICGN mice. Error bars represent standard error. Five ICB2-1 mice, three ICB2-2 mice and eight ICB2-3 mice, two ICB2-4 mice, eight ICB2-5 mice and seven ICB2-6 mice were analyzed