Abstract 122: Deletion of Gstm1 Results in Poor Survival and Exaggerated Kidney Injury Associated With Increased Oxidative Stress and Apoptosis in a Mouse Model of Chronic Kidney Disease

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In humans, a common deletion variant of the GSTM1 gene, the GSTM1(0) null allele, results in decreased GSTM1 enzymatic activity and is associated with higher levels of oxidative stress. We reported that GSTM1(0) is associated with increased risks of chronic kidney disease (CKD) progression and death in the African Americans Study of Kidney Disease. To establish a causal relationship between GSTM1 deficiency and CKD progression, we deleted Gstm1 in the mouse, and determined its effect in the sub-total nephrectomy (Nx) model of CKD. After the 8 th week after Nx, 4 out of 8 Gstm1 knockout (KO) mice began to die, whereas wild-type (WT) mice had 100% survival by the study endpoint at 13 th week. Remaining KO mice had significantly higher plasma creatinine (p < 0.05), suggestive of lower GFR. Due to early mortality in KO mice after the 8th week after Nx, we phenotyped mice at the 8 th week (n=6 each). KO mice had significantly higher 1) mean systolic blood pressure (by radiotelemetry): KO 157.2 ± 5, WT 141.1 ± 2.4 mmHg, 2) urine albumin/creatinine ratio (μg/mg): KO 748.4 ± 187.9, WT 235.1 ± 24.6, and 3) renal superoxide (O2·-) levels (counts/min/mg dry tissue): KO 249.7 ± 63; WT 74.5 ± 14.7; P ≤ 0.02. Hydrogen peroxide levels were not different. Renal mRNA levels of the superoxide dismutase isoforms SOD1, SOD2, and SOD3 were significantly lower in KO mice (KO 7.78 ± 0.047, 0.446 ± 0.062, 0.18 ± 0.03; WT 10.64 ± 0.43, 2.432 ± 0.386, 1.188 ± 0.124, respectively, P ≤ 0.003. Total kidney pathology score (KO 18.7 ± 1.5; WT 8 ± 0.6; P <0.0001) showed that KO mice had worse kidney injury, with severe glomerulosclerosis, proteinaceous casts, and chronic inflammation. Both glomerular surface area (SA)/total non-infarcted kidney area (KO 3.347 ± 0.301; WT 2.286 ± 0.268; P = 0.02) and mesangial SA/glomerular SA (KO 35.62 ± 2.219; WT 23.6 ± 2.569; P = 0.005) were significantly increased in KO mice. GSTM1 has also been shown to suppress ASK1 - the apoptosis signal-regulating kinase 1 that induces apoptosis via activation of caspase-3. Consistent with activated ASK1 pathway, KO mice had significantly higher renal TUNEL staining and caspase-3 protein levels (KO 3.594 ± 0.327; WT 2.511 ± 0.208; P = 0.01). In conclusion, in CKD, loss of GSTM1 leads to deleterious outcome associated with increased O2·- levels and apoptosis.