Refining the Mouse Subtotal Nephrectomy in Male 129S2/SV Mice for Consistent Modeling of Progressive Kidney Disease With Renal Inflammation and Cardiac Dysfunction

Beta Blockade Prevents Cardiac Morphological and Molecular Remodelling in Experimental Uremia

Heart failure and chronic kidney disease (CKD) share several mediators of cardiac pathological remodelling. Akin to heart failure, this remodelling sets in motion a vicious cycle of progressive pathological hypertrophy and myocardial dysfunction in CKD. Several decades of heart failure research have shown that beta blockade is a powerful tool in preventing cardiac remodelling and breaking this vicious cycle. This phenomenon remains hitherto untested in CKD. Therefore, we set out to test the hypothesis that beta blockade prevents cardiac pathological remodelling in experimental uremia. Wistar rats had subtotal nephrectomy or sham surgery and were followed up for 10 weeks. The animals were randomly allocated to the beta blocker metoprolol (10 mg/kg/day) or vehicle. In vivo and in vitro cardiac assessments were performed. Cardiac tissue was extracted, and protein expression was quantified using immunoblotting. Histological analyses were performed to quantify myocardial fibrosis. Beta blockade attenuated cardiac pathological remodelling in nephrectomised animals. The echocardiographic left ventricular mass and the heart weight to tibial length ratio were significantly lower in nephrectomised animals treated with metoprolol. Furthermore, beta blockade attenuated myocardial fibrosis associated with subtotal nephrectomy. In addition, the Ca++- calmodulin-dependent kinase II (CAMKII) pathway was shown to be activated in uremia and attenuated by beta blockade, offering a potential mechanism of action. In conclusion, beta blockade attenuated hypertrophic signalling pathways and ameliorated cardiac pathological remodelling in experimental uremia. The study provides a strong scientific rationale for repurposing beta blockers, a tried and tested treatment in heart failure, for the benefit of patients with CKD.

Mapping the Transcriptome Underpinning Acute Corticosteroid Action within the Cortical Collecting Duct

Key Points

We report the transcriptomes associated with acute corticosteroid regulation of ENaC activity in polarized mCCDcl1 collecting duct cells. Nine genes were regulated by aldosterone (ALDO), 0 with corticosterone alone, and 151 with corticosterone when 11βHSD2 activity was inhibited. We validated three novel ALDO-induced genes, Rasd1 , Sult1d1 , and Gm43305 , in primary cells isolated from a novel principal cell reporter mouse.

Background

Corticosteroids regulate distal nephron and collecting duct (CD) Na+ reabsorption, contributing to fluid-volume and blood pressure homeostasis. The transcriptional landscape underpinning the acute stimulation of the epithelial sodium channel (ENaC) by physiological concentrations of corticosteroids remains unclear.

Methods

Transcriptomic profiles underlying corticosteroid-stimulated ENaC activity in polarized mCCDcl1 cells were generated by coupling electrophysiological measurements of amiloride-sensitive currents with RNAseq. Generation of a principal cell-specific reporter mouse line, mT/mG -Aqp2Cre, enabled isolation of primary CD principal cells by FACS, and ENaC activity was measured in cultured primary cells after acute application of corticosteroids. Expression of target genes was assessed by qRT-PCR in cultured cells or freshly isolated cells after the acute elevation of steroid hormones in mT/mG -Aqp2Cre mice.

Results

Physiological relevance of the mCCDcl1 model was confirmed with aldosterone (ALDO)-specific stimulation of SGK1 and ENaC activity. Corticosterone (CORT) only modulated these responses at supraphysiological concentrations or when 11βHSD2 was inhibited. When 11βHSD2 protection was intact, CORT caused no significant change in transcripts. We identified a small number of ALDO-induced transcripts associated with stimulated ENaC activity in mCCDcl1 cells and a much larger number with CORT in the absence of 11βHSD2 activity. Principal cells isolated from mT/mG -Aqp2Cre mice were validated and assessment of identified ALDO-induced genes revealed that Sgk1 , Zbtbt16 , Sult1d1 , Rasd1 , and Gm43305 are acutely upregulated by corticosteroids both in vitro and in vivo .

Conclusions

This study reports the transcriptome of mCCDcl1 cells and identifies a small number of ALDO-induced genes associated with acute stimulation of ENaC, including three previously undescribed genes.

Pro-oxidative priming but maintained cardiac function in a broad spectrum of murine models of chronic kidney disease

Aims

Patients with chronic kidney disease (CKD) have an increased risk of cardiovascular events and exhibit myocardial changes including left ventricular (LV) hypertrophy and fibrosis, overall referred to as ‘uremic cardiomyopathy’. Although different CKD animal models have been studied for cardiac effects, lack of consistent reporting on cardiac function and pathology complicates clear comparison of these models. Therefore, this study aimed at a systematic and comprehensive comparison of cardiac function and cardiac pathophysiological characteristics in eight different CKD models and mouse strains, with a main focus on adenine-induced CKD.

Methods and results

CKD of different severity and duration was induced by subtotal nephrectomy or adenine-rich diet in various strains (C57BL/6J, C57BL/6 N, hyperlipidemic C57BL/6J ApoE^−/−, 129/Sv), followed by the analysis of kidney function and morphology, blood pressure, cardiac function, cardiac hypertrophy, fibrosis, myocardial calcification and inflammation using functional, histological and molecular techniques, including cardiac gene expression profiling supplemented by oxidative stress analysis. Intriguingly, despite uremia of variable degree, neither cardiac dysfunction, hypertrophy nor interstitial fibrosis were observed. However, already moderate CKD altered cardiac oxidative stress responses and enhanced oxidative stress markers in each mouse strain, with cardiac RNA sequencing revealing activation of oxidative stress signaling as well as anti-inflammatory feedback responses.

Conclusion

This study considerably expands the knowledge on strain- and protocol-specific differences in the field of cardiorenal research and reveals that several weeks of at least moderate experimental CKD increase oxidative stress responses in the heart in a broad spectrum of mouse models. However, this was insufficient to induce relevant systolic or diastolic dysfunction, suggesting that additional “hits” are required to induce uremic cardiomyopathy.

Translational perspective

Patients with chronic kidney disease (CKD) have an increased risk of cardiovascular adverse events and exhibit myocardial changes, overall referred to as ‘uremic cardiomyopathy’. We revealed that CKD increases cardiac oxidative stress responses in the heart. Nonetheless, several weeks of at least moderate experimental CKD do not necessarily trigger cardiac dysfunction and remodeling, suggesting that additional “hits” are required to induce uremic cardiomyopathy in the clinical setting. Whether the altered cardiac oxidative stress balance in CKD may increase the risk and extent of cardiovascular damage upon additional cardiovascular risk factors and/or events will be addressed in future studies.

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Development of a CKD mouse model with a clear cardiac functional or morphological phenotype is challenging.

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Cardiac oxidative stress response as well as oxidative stress markers are increased in a broad spectrum of CKD mouse models.

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Our findings suggest need of additional cardiovascular hits to clearly induce uremic cardiomyopathy as observed in patients.

A systematic review and meta-analysis of murine models of uremic cardiomyopathy

Chronic kidney disease (CKD) triggers the risk of developing uremic cardiomyopathy as characterized by cardiac hypertrophy, fibrosis and functional impairment. Traditionally, animal studies are used to reveal the underlying pathological mechanism, although variable CKD models, mouse strains and readouts may reveal diverse results. Here, we systematically reviewed 88 studies and performed meta-analyses of 52 to support finding suitable animal models for future experimental studies on pathological kidney-heart crosstalk during uremic cardiomyopathy. We compared different mouse strains and the direct effect of CKD on cardiac hypertrophy, fibrosis and cardiac function in "single hit" strategies as well as cardiac effects of kidney injury combined with additional cardiovascular risk factors in "multifactorial hit" strategies. In C57BL/6 mice, CKD was associated with a mild increase in cardiac hypertrophy and fibrosis and marginal systolic dysfunction. Studies revealed high variability in results, especially regarding hypertrophy and systolic function. Cardiac hypertrophy in CKD was more consistently observed in 129/Sv mice, which express two instead of one renin gene and more consistently develop increased blood pressure upon CKD induction. Overall, "multifactorial hit" models more consistently induced cardiac hypertrophy and fibrosis compared to "single hit" kidney injury models. Thus, genetic factors and additional cardiovascular risk factors can "prime" for susceptibility to organ damage, with increased blood pressure, cardiac hypertrophy and early cardiac fibrosis more consistently observed in 129/Sv compared to C57BL/6 strains.

Myeloid Heterogeneity in Kidney Disease as Revealed through Single-Cell RNA Sequencing

Kidney disease represents a global health burden of increasing prevalence and is an independent risk factor for cardiovascular disease. Myeloid cells are a major cellular compartment of the immune system; they are found in the healthy kidney and in increased numbers in the damaged and/or diseased kidney, where they act as key players in the progression of injury, inflammation, and fibrosis. They possess enormous plasticity and heterogeneity, adopting different phenotypic and functional characteristics in response to stimuli in the local milieu. Although this inherent complexity remains to be fully understood in the kidney, advances in single-cell genomics promise to change this. Specifically, single-cell RNA sequencing (scRNA-seq) has had a transformative effect on kidney research, enabling the profiling and analysis of the transcriptomes of single cells at unprecedented resolution and throughput, and subsequent generation of cell atlases. Moving forward, combining scRNA- and single-nuclear RNA-seq with greater-resolution spatial transcriptomics will allow spatial mapping of kidney disease of varying etiology to further reveal the patterning of immune cells and nonimmune renal cells. This review summarizes the roles of myeloid cells in kidney health and disease, the experimental workflow in currently available scRNA-seq technologies, and published findings using scRNA-seq in the context of myeloid cells and the kidney.

Skeletal myopathy in CKD: a comparison of adenine-induced nephropathy and 5/6 nephrectomy models in mice

Preclinical animal models of chronic kidney disease (CKD) are critical to investigate the underlying mechanisms of disease and to evaluate the efficacy of novel therapeutics aimed to treat CKD-associated pathologies. The objective of the present study was to compare the adenine diet and 5/6 nephrectomy (Nx) CKD models in mice. Male and female 10-wk-old C57BL/6J mice (n = 5-9 mice/sex/group) were randomly allocated to CKD groups (0.2-0.15% adenine-supplemented diet or 5/6 Nx surgery) or the corresponding control groups (casein diet or sham surgery). Following the induction of CKD, the glomerular filtration rate was reduced to a similar level in both adenine and 5/6 Nx mice (adenine diet-fed male mice: 81.1 ± 41.9 µL/min vs. 5/6 Nx male mice: 160 ± 80.9 µL/min, P = 0.5875; adenine diet-fed female mice: 112.9 ± 32.4 µL/min vs. 5/6 Nx female mice: 107.0 ± 45.7 µL/min, P = 0.9995). Serum metabolomics analysis indicated that established uremic toxins were robustly elevated in both CKD models, although some differences were observed between CKD models (i.e., p-cresol sulfate). Dysregulated phosphate homeostasis was observed in the adenine model only, whereas Ca2+ homeostasis was disturbed in male mice with both CKD models. Compared with control mice, muscle mass and myofiber cross-sectional areas of the extensor digitorum longus and soleus muscles were ∼18-24% smaller in male CKD mice regardless of the model but were not different in female CKD mice (P > 0.05). Skeletal muscle mitochondrial respiratory function was significantly decreased (19-24%) in CKD mice in both models and sexes. These findings demonstrate that adenine diet and 5/6 Nx models of CKD have similar levels of renal dysfunction and skeletal myopathy. However, the adenine diet model demonstrated superior performance with regard to mortality (∼20-50% mortality for 5/6 Nx vs. 0% mortality for the adenine diet, P < 0.05 for both sexes) compared with the 5/6 Nx surgical model.NEW & NOTEWORTHY Numerous preclinical models of chronic kidney disease have been used to evaluate skeletal muscle pathology; however, direct comparisons of popular models are not available. In this study, we compared adenine-induced nephropathy and 5/6 nephrectomy models. Both models produced equivalent levels of muscle atrophy and mitochondrial impairment, but the adenine model exhibited lower mortality rates, higher consistency in uremic toxin levels, and dysregulated phosphate homeostasis compared with the 5/6 nephrectomy model.

Shunaoxin pills improve the antihypertensive effect of nifedipine and alleviate its renal lipotoxicity in spontaneous hypertension rats

Shunaoxin pills (SNX) have been used to treat cerebrovascular diseases in China since 2005. Hypertension is a major risk factor for cerebrovascular disease. This study aimed to explore the synergistic antihypertensive effect of SNX and nifedipine and whether SNX could alleviate nifedipine-induced renal lipotoxicity. During administration, systolic blood pressure was measured weekly. After 5 weeks administration, we examined pathological changes of kidney, renal function, the lipid metabolism index, and adipogenesis genes expression in the kidney tissues, and explored its underlying mechanism. Finally, network pharmacology was used for supplement and verification. As a result, SNX improved the antihypertensive effect of nifedipine and apparently improved nifedipine-induced renal pathological changes, dyslipidemia and the levels of adipogenesis gene expression in kidney tissues. SNX reduced the levels of interleukin-6 and interleukin-1β in renal tissues, down-regulated the production of malondialdehyde, and increased superoxide dismutase activity and the protein expression of heme oxygenase-1 in kidney tissues. Network pharmacology also showed that SNX could improve nifedipine-induced renal lipotoxicity. The combination of SNX and nifedipine had certain benefits in the treatment of hypertension.