A mutation in the mouse Chd2 chromatin remodeling enzyme results in a complex renal phenotype

Abstract

Background and aims: Glomerular diseases are the third leading cause of kidney failure worldwide, behind only diabetes and hypertension. The molecular mechanisms underlying the cause of glomerular diseases are still largely unknown. The identification and characterization of new molecules associated with glomerular function should provide new insights into understanding the diverse group of glomerular diseases. The Chd2 protein belongs to a family of enzymes involved in ATP-dependent chromatin remodeling, suggesting that it likely functions as an epigenetic regulator of gene expression via the modification of chromatin structure.

Methods: In this study, we present a detailed histomorphologic characterization of mice containing a mutation in the chromodomain helicase DNA-binding protein 2 (Chd2).

Results: We show that Chd2-mutant mice present with glomerulopathy, proteinuria, and significantly impaired kidney function. Additionally, serum analysis revealed decreased hemoglobin and hematocrit levels in Chd2-mutant mice, suggesting that the glomerulopathy observed in these mice is associated with anemia.

Conclusion: Collectively, the data suggest a role for the Chd2 protein in the maintenance of kidney function.

Fig. 1.

Structural alterations in kidneys of Chd2^+/mut mice. HEstained kidney sections from terminally ill, end-stage Chd2^+/mut mice ranging from 5 to 9 months of age and their age- and sexmatched wild-type (WT) littermates. a, b The cortex of the heterozygous glomerulus (arrow) is enlarged due to global matrix deposition, which is not seen in the WT glomerulus. Note the inflammatory cells (∗) present in the cortical interstitium of Chd2^+/mut mice. c, d In contrast to the normal tubules in the renal cortex of WT mice, tubular dilatation (TD) is observed in Chd2^+/mut mice. e, f Tubulointerstitial lesions with dilation of tubules, tubular atrophy, and interstitial nephritis are seen in Chd2^+/mut kidney sections, but not in the WT littermates. Note the inflammatory cells within the tubular lumens of Chd2^+/mut kidney. g, h Marked atrophy of the papilla (∗) is observed in the renal medulla of the Chd2^+/mut kidney compared with the WT control. i, j The capsule of the Chd2^+/mut kidney is irregular in shape (arrow) compared to the normal capsule (arrow) of the WT control mice. Images were taken with the objective lens magnification denoted in each panel.

Fig. 2.

Chd2^+/mut mice present with glomerulopathy. Images display representative kidney sections from terminally ill, end-stage Chd2^+/mut mice and their ageand sex-matched WT littermates stained with periodic acid-Schiff (PAS) and trichrome. a, b PAS staining reveals that the Chd2 heterozygous glomerulus shows segmental thickening of basement membrane regions (arrow) due to PAS positive matrix deposition, which is not seen in the WT glomerulus. c, d Increased collagen deposition (light blue) within the glomerulus and regions surrounding the glomerulus is observed in the Chd2^+/mut kidney stained with trichrome compared to the WT control. Images were taken with the objective lens magnification denoted in each panel.

Fig. 3.

Proteinuria in Chd2^+/mut mice. Representative images of HE-stained kidney sections from terminally ill, end-stage Chd2^+/mut mice and their age- and sex-matched WT littermates. Protein was not observed in either the Bowman's space (a) or the tubules (c) of the WT mice. Prominent protein casts (∗) were present within the Bowman's space (b) and within dilated tubules (d) of the Chd2^+/mut mice. Images were taken with the objective lens denoted in each panel. e SDS-PAGE analysis of urinary protein in WT and mutant mice. An equal volume of urine from each mouse (lanes 1–3) and purified bovine serum albumin (BSA) (lane 4) were electrophoresed on an SDS polyacrylamide gel, and protein bands were visualized by staining with Coomassie brilliant blue. Various amounts of albumin (66 kDa) were observed in Chd2^+/mut mice. Low-molecular-weight proteins (∼ 20 kDa) were present in all urine samples and serve as a loading control. f Decreased levels of serum albumin were detected in Chd2^+/mut mice in comparison to their Chd2^+/+ littermates. For these analyses, n = 7 for both genotypes. g In contrast to Chd2^+/+ mice, decreased levels of total serum protein were detected in the Chd2^+/mut mice (n = 7 for both genotypes).

Fig. 4.

Chd2^+/mut mice present with azotemia. Elevated levels of serum creatinine (a) and urea nitrogen (b) are observed in terminally ill, end-stage Chd2^+/mut mice. (∗) indicates an outlier obtained from a Chd2^+/mut mouse. For these analyses, n = 7 for both genotypes.

Fig. 5.

Chd2^+/mut mice are anemic. a Decreased levels of erythropoietin (EPO) are observed in Chd2^+/mut mice in comparison to the Chd2^+/+ mice. For these analyses, n = 7 for both genotypes. EPO transcript levels were normalized to EF-1α mRNA levels, and the wild-type values were set to 1.0. Differences in hemoglobin (Hb) levels (b) and hematocrit (Hct) levels (c) show that Chd2^+/mut are anemic. For these analyses, n = 3 for Chd2^+/+ mice and n = 5 for Chd2^+/mut mice.