No abstract

Recently, we reported that obese Dahl salt-sensitive (SS) leptin receptor mutant (SSLepRmutant) rats display progressive renal injury. The present study demonstrated that the early development of renal injury in the SSLepRmutant strain is associated with an increase in the renal infiltration of macrophages compared with lean SS rats. We also examined whether depletion of macrophages with clodronate would reduce the early progression of renal injury in the SSLepRmutant strain. Four-week-old SS and SSLepRmutant rats were treated with either vehicle (PBS) or clodronate (50 mg/kg ip, 2 times/wk) for 4 wk. While the administration of clodronate did not reduce renal macrophage infiltration in SS rats, clodronate decreased macrophages in the kidneys of SSLepRmutant rats by >50%. Interestingly, clodronate significantly reduced plasma glucose, insulin, and triglyceride levels and markedly improved glucose tolerance in SSLepRmutant rats. Treatment with clodronate had no effect on the progression of proteinuria or renal histopathology in SS rats. In the SSLepRmutant strain, proteinuria was markedly reduced during the first 2 wk of treatment (159 ± 32 vs. 303 ± 52 mg/day, respectively). However, after 4 wk of treatment, the effect of clodronate was no longer observed in the SSLepRmutant strain (346 ± 195 vs. 399 ± 50 mg/day, respectively). The kidneys from SSLepRmutant rats displayed glomerular injury with increased mesangial expansion and renal fibrosis versus SS rats. Treatment with clodronate significantly decreased glomerular injury and renal fibrosis in the SSLepRmutant strain. Overall, these data indicate that the depletion of macrophages improves metabolic disease and slows the early progression of renal injury in SSLepRmutant rats.

Recently, we reported that obese Dahl salt-sensitive leptin receptor mutant (SSLepRmutant) rats develop glomerular injury and progressive proteinuria prior to puberty. Moreover, this early progression of proteinuria was associated with elevations in GFR. Therefore, the current study examined whether treatment with lisinopril to reduce GFR slows the early progression of proteinuria in SSLepRmutant rats prior to puberty. Experiments were performed on 4-week-old SS and SSLepRmutant rats that were either treated with vehicle or lisinopril (20 mg/kg/day, drinking water) for 4 weeks. We did not observe any differences in MAP between SS and SSLepRmutant rats treated with vehicle (148 ± 5 vs. 163 ± 6 mmHg, respectively). Interestingly, chronic treatment with lisinopril markedly reduced MAP in SS rats (111 ± 3 mmHg) but had no effect on MAP in SSLepRmutant rats (155 ± 4 mmHg). Treatment with lisinopril significantly reduced proteinuria in SS and SSLepRmutant rats compared to their vehicle counterparts (19 ± 5 and 258 ± 34 vs. 71 ± 12 and 498 ± 66 mg/day, respectively). Additionally, nephrin excretion was significantly elevated in SSLepRmutant rats versus SS rats, and lisinopril reduced nephrin excretion in both strains. GFR was significantly elevated in SSLepRmutant rats compared to SS rats, and lisinopril treatment reduced GFR in SSLepRmutant rats by 30%. The kidneys from SSLepRmutant rats displayed glomerular injury with increased mesangial expansion and renal inflammation versus SS rats. Chronic treatment with lisinopril significantly decreased glomerular injury and renal inflammation in the SSLepRmutant rats. Overall, these data indicate that inhibiting renal hyperfiltration associated with obesity is beneficial in slowing the early development of glomerular injury and renal inflammation.

Prepubertal (PPO) obesity has emerged as a major health problem over the last few decades and is a risk factor for the development of proteinuria. The current study investigated whether the development of renal injury in the obese SSLepRmutant strain occurs prior to puberty. When determining the temporal changes in serum sex hormones in female and male SS and SSLepRmutant rats between 4 and 10 weeks of age, we only observed significant increases in estradiol and testosterone levels in female and male SS rats at 10 weeks of age compared to 4 weeks of age. The results suggest that studying both strains between 4 and 8 weeks of age is appropriate to study the effects of PPO on renal injury in this model. Proteinuria was significantly higher in SSLepRmutant rats as opposed to the values observed in SS rats at 8 weeks of age, and we did not observe any sex differences in proteinuria in either strain. The kidneys from the SSLepRmutant rats displayed significant glomerular and tubular injury and renal fibrosis versus the values measured in SS rats without any sex differences. Overall, we observed increased immune cell infiltration in the kidneys from SSLepRmutant rats compared to SS rats. Interestingly, female SSLepRmutant rats displayed significant increases in not only M1 macrophages (pro-inflammatory) but also M2 macrophages (anti-inflammatory) versus male SSLepRmutant rats. These results suggest the SSLepRmutant rat may be a useful model to study early progression of obesity-related renal injury prior to the onset of puberty.

List of abbreviations: ACE, angiotensin-converting enzyme; AKI, acute kidney injury; APC, allophycocyanin; BV421, brilliant violet TM 421; CCL20, chemokine (c-c) ligand 20; CD, cluster of differentiation; CKD, chronic kidney disease; DC, dendritic cell; DNase, deoxyribonuclease; FACS, fluorescence activated and cell sorting; FITC, fluorescein isothiocyanate; FOXP3, forkhead box P3; FSC, forward scatter; GFR, glomerular filtration rate; IgG, immunoglobulin G; IL2, interleukin-2; IL4, interleukin-4; IL10, interleukin-10; IL17, interleukin-17; KIM-1, kidney injury molecule-1; MIP3a, macrophage inflammatory protein 3a g antibody; NGAL, neutrophil gelatinase-associated lipocalin; PAS, periodic acid Schiff; PE, phycoerythrin; PerCP, peridinin-chlorophyll protein; RAS, reninretinoic acid-related orphan receptor-stitute (buffer); SS, Dahl salt-sensitive (rat); SSC, side scatter; SS LepR mutant, Dahl salt-sensitive leptin receptor mutant (rat).