Blockade of the natriuretic peptide clearance receptor attenuates proteinuria in a mouse model of focal segmental glomerulosclerosis

Podocyte specific knockout of the natriuretic peptide clearance receptor is podocyte protective in focal segmental glomerulosclerosis

Natriuretic peptides (NPs) bind to glomerular podocytes and attenuate glomerular injury. The beneficial effects of NPs are negatively regulated by the NP clearance receptor (NPRC), which is highly expressed in podocytes. To determine if inhibiting NPRC is podocyte protective, we examined the effects of deleting NPRC in both cultured podocytes and in vivo. We found that: 1.Both atrial NP and C-type NP inhibit podocyte apoptosis in cultured podocytes, but these podocyte protective effects are significantly attenuated in cells expressing NPRC, and 2. Atrial NP was significantly more effective than CNP at inhibiting the apoptotic response. Consistent with the protective actions of NPs, podocyte specific knockout of NPRC reduced albuminuria, glomerular sclerosis and tubulointerstitial inflammation in a mouse model of focal segmental glomerulosclerosis. These beneficial actions were associated with: 1. Decreased expression of the myofibroblast marker alpha-smooth muscle actin, 2. Reduced expression of the extracellular matrix proteins collagen 4-alpha-1 and fibronectin, and 3. Preserved expression of the podocyte proteins nephrin and podocin. Inhibiting NP clearance may be a useful therapeutic approach to treat glomerular diseases.

Real-time imaging of cGMP signaling shows pronounced differences between glomerular endothelial cells and podocytes

Recent clinical trials of drugs enhancing cyclic guanosine monophosphate (cGMP) signaling for cardiovascular diseases have renewed interest in cGMP biology within the kidney. However, the role of cGMP signaling in glomerular endothelial cells (GECs) and podocytes remains largely unexplored. Using acute kidney slices from mice expressing the FRET-based cGMP biosensor cGi500 in endothelial cells or podocytes enabled real-time visualization of cGMP. Stimulation with atrial natriuretic peptide (ANP) or SNAP (NO donor) and various phosphodiesterase (PDE) inhibitors elevated intracellular cGMP in both cell types. GECs showed a transient cGMP response upon particulate or soluble guanylyl cyclase activation, while the cGMP response in podocytes reached a plateau following ANP administration. Co-stimulation (ANP + SNAP) led to an additive response in GECs. The administration of PDE inhibitors revealed a broader basal PDE activity in GECs dominated by PDE2a. In podocytes, basal PDE activity was mainly restricted to PDE3 and PDE5 activity. Our data demonstrate the existence of both guanylyl cyclase pathways in GECs and podocytes with cell-specific differences in cGMP synthesis and degradation, potentially suggesting new therapeutic options for kidney diseases.

Podocyte cell-specific Npr1 is required for blood pressure and renal homeostasis in male and female mice: role of sex-specific differences

Atrial and brain natriuretic peptides (ANP and BNP) bind to guanylyl cyclase A/natriuretic peptide receptor A (GC-A/NPRA), stimulating natriuresis and diuresis and reducing blood pressure (BP), but the role of ANP/NPRA signaling in podocytes (highly specialized epithelial cells covering the outer surfaces of renal glomerular capillaries) remains unclear. This study aimed to determine the effect of conditional deletion of podocyte-specific Npr1 (encoding NPRA) gene knockout (KO) in male and female mice. Tamoxifen-treated wild-type control (PD Npr1 f/f; WT), heterozygous (PD-Cre-Npr1 f/+; HT), and KO (PD-Cre-Npr1 f/-) mice were fed a normal-, low-, or high-salt diet for 4 wk. Podocytes isolated from HT and KO male and female mice showed complete absence of Npr1 mRNA and NPRA protein compared with WT mice. BP, plasma creatinine, plasma sodium, urinary protein, and albumin/creatinine ratio were significantly increased, whereas plasma total protein, albumin, creatinine clearance, and urinary sodium levels were significantly reduced in the HT and KO male and female mice compared with WT mice. These changes were significantly greater in males than in females. On a normal-salt diet, glomerular filtration rate was significantly decreased in PD Npr1 HT and KO male and female mice compared with WT mice. Immunofluorescence of podocin and synaptopodin was also significantly reduced in HT and KO mice compared with WT mice. These observations suggest that in podocytes, ANP/NPRA signaling may be crucial in the maintenance and regulation of glomerular filtration and BP and serve as a biomarker of renal function in a sex-dependent manner.NEW & NOTEWORTHY Our results demonstrate that the podocyte-specific deletion of Npr1 showed increased blood pressure (BP) and altered biomarkers of renal functions, with greater magnitudes in animals fed a high-salt diet in a sex-dependent manner. The results suggest a direct and sex-dependent effect of Npr1 ablation in podocytes on the regulation of BP and renal function and reveal that podocytes may be considered an important target for the ANP-BNP/NPRA/cGMP signaling cascade.

C-type natriuretic peptide (CNP): The cardiovascular system and beyond

C-type natriuretic peptide (CNP) represents the 'local' member of the natriuretic peptide family, functioning in an autocrine or paracrine capacity to modulate a hugely diverse portfolio of physiological processes. Whilst the best-characterised of these regulatory roles are in the cardiovascular system, akin to its predominantly endocrine siblings atrial (ANP) and brain (BNP) natriuretic peptides, CNP governs many additional, unrelated mechanisms including bone growth, gamete maturation, auditory processing, and neuronal integrity. Furthermore, there is currently great interest in mimicking the biological activity of CNP for therapeutic gain in many of these disparate organ systems. Herein, we provide an overview of the physiology, pathophysiology and pharmacology of CNP in both cardiovascular and non-cardiovascular settings.

Unraveling the role of natriuretic peptide clearance receptor (NPR3) in glomerular diseases

Natriuretic peptides (NPs) are cardio-derived hormones that have a crucial role in maintaining cardiovascular homeostasis. Physiological effects of NPs are mediated by binding to natriuretic peptide receptors 1 and 2 (NPR1/2), whereas natriuretic peptide receptor 3 (NPR3) acts as a clearance receptor that removes NPs from the circulation. Mouse studies have shown that local NP-signaling in the kidney glomerulus is important for the maintenance of renal homeostasis. In this study we examined the expression of NPR3 in kidney tissue and explored its involvement in renal physiology and disease by generating podocyte-specific knockout mice (NPR3podKO) as well as by using an NPR3 inhibitor (NPR3i) in rodent models of kidney disease. NPR3 was highly expressed by podocytes. NPR3podKO animals showed no renal abnormalities under healthy conditions and responded similarly to nephrotoxic serum (NTS) induced glomerular injury. However, NPR3i showed reno-protective effects in the NTS-induced model evidenced by decreased glomerulosclerosis and reduced podocyte loss. In a ZSF1 rat model of diabetic kidney injury, therapy alone with NPR3i did not have beneficial effects on renal function/histology, but when combined with losartan (angiotensin receptor blocker), NPR3i potentiated its ameliorative effects on albuminuria. In conclusion, these results suggest that NPR3 may contribute to kidney disease progression.

Pharmacologic blockade of the natriuretic peptide clearance receptor promotes weight loss and enhances insulin sensitivity in type 2 diabetes

While natriuretic peptides (NPs) are primarily known for their renal and cardiovascular actions, NPs stimulate lipolysis in adipocytes and induce a thermogenic program in white adipose tissue (WAT) that resembles brown fat. The biologic effects of NPs are negatively regulated by the NP clearance receptor (NPRC), which binds and degrades NPs. Knockout (KO) of NPRC protects against diet induced obesity and improves insulin sensitivity in obese mice. To determine if pharmacologic blockade of NPRC enhanced the beneficial metabolic actions of NPs in type 2 diabetes, we blocked NP clearance in a mouse model of type 2 diabetes using the specific NPRC ligand ANP(4-23). We found that treatment with ANP(4-23) caused a significant decrease in body weight by increasing energy expenditure and reducing fat mass without a change in lean body mass. The decrease in fat mass was associated with a significant improvement in insulin sensitivity and reduced serum insulin levels. These beneficial effects were accompanied by a decrease in infiltrating macrophages in adipose tissue, and reduced expression of inflammatory markers in both serum and WAT. These data suggest that inhibiting NP clearance may be an effective pharmacologic approach to promote weight loss and enhance insulin sensitivity in type 2 diabetes. Optimizing the therapeutic approach may lead to useful therapies for obesity and type 2 diabetes.