Urinary C-type natriuretic peptide excretion: a potential novel biomarker for renal fibrosis during aging

Evidence for Angiotensin II as a Naturally Existing Suppressor for the Guanylyl Cyclase A Receptor and Cyclic GMP Generation

The natriuretic peptide system (NPS) and renin-angiotensin-aldosterone system (RAAS) function oppositely at multiple levels. While it has long been suspected that angiotensin II (ANGII) may directly suppress NPS activity, no clear evidence to date supports this notion. This study was designed to systematically investigate ANGII-NPS interaction in humans, in vivo, and in vitro. Circulating atrial, b-type, and c-type natriuretic peptides (ANP, BNP, CNP), cyclic guanosine monophosphate (cGMP), and ANGII were simultaneously investigated in 128 human subjects. Prompted hypothesis was validated in vivo to determine the influence of ANGII on ANP actions. The underlying mechanisms were further explored via in vitro approaches. In humans, ANGII demonstrated an inverse relationship with ANP, BNP, and cGMP. In regression models predicting cGMP, adding ANGII levels and the interaction term between ANGII and natriuretic peptides increased the predictive accuracy of the base models constructed with either ANP or BNP, but not CNP. Importantly, stratified correlation analysis further revealed a positive association between cGMP and ANP or BNP only in subjects with low, but not high, ANGII levels. In rats, co-infusion of ANGII even at a physiological dose attenuated cGMP generation mediated by ANP infusion. In vitro, we found the suppressive effect of ANGII on ANP-stimulated cGMP requires the presence of ANGII type-1 (AT1) receptor and mechanistically involves protein kinase C (PKC), as this suppression can be substantially rescued by either valsartan (AT1 blocker) or Go6983 (PKC inhibitor). Using surface plasmon resonance (SPR), we showed ANGII has low binding affinity to the guanylyl cyclase A (GC-A) receptor compared to ANP or BNP. Our study reveals ANGII is a natural suppressor for the cGMP-generating action of GC-A via AT1/PKC dependent manner and highlights the importance of dual-targeting RAAS and NPS in maximizing beneficial properties of natriuretic peptides in cardiovascular protection.

EVIDENCE FOR ANGIOTENSIN II AS A NATURALLY EXISTING SUPPRESSOR FOR THE NATRIURETIC PEPTIDE SYSTEM

Background

Natriuretic peptide system (NPS) and renin angiotensin aldosterone system (RAAS) function oppositely at multiple levels. While it has long been suspected that angiotensin II (ANGII) may directly suppress NPS activity, no clear evidence to date support this notion.

Objectives

This study was designed to systematically investigate ANGII-NPS interaction in humans, in vivo, and in vitro for translational insights.

Methods

Circulating atrial, b-type, and c-type natriuretic peptides (ANP, BNP, CNP), cyclic guanosine monophosphate (cGMP), and ANGII were simultaneously investigated in 128 human subjects. Prompted hypothesis was validated in rat model to determine influence of ANGII on ANP actions. Multiple engineered HEK293 cells and surface plasmon resonance (SPR) technology were leveraged for mechanistic exploration.

Results

In humans, ANGII showed inverse relationship with ANP, BNP, and cGMP. In regression models predicting cGMP, adding ANGII levels and interaction term between ANGII and natriuretic peptide increased predicting accuracy of base models constructed with either ANP or BNP, but not CNP. Importantly, stratified correlation analysis further revealed positive association between cGMP with ANP or BNP only in subjects with low, but not high, ANGII levels. In rats, co-infusion of ANGII even at physiological dose attenuated blood pressure reduction and cGMP generation triggered by ANP infusion. In vitro, we showed that the suppression effect of ANGII on ANP-stimulated cGMP requires the presence of ANGII type-1 (AT1) receptor and mechanistically involves protein kinase C (PKC), which can be substantially rescued by either valsartan (AT1 blocker) or Go6983 (PKC inhibitor). Using SPR, we showed ANGII has low affinity for particulate guanylyl cyclase A (GC-A) receptor binding compared to ANP or BNP.

Conclusions

Our study reveals ANGII as a natural suppressor for cGMP-generating action of GC-A via AT1/PKC dependent manner and highlights importance of dual-targeting RAAS and NPS in maximizing beneficial properties of natriuretic peptides in cardiovascular disease.

Sex-Mediated Differences in TNF Signaling- and ECM-Related Gene Expression in Aged Rat Kidney

Aging leads to the functional decline of an organism, which is associated with age and sex. To understand the functional change of kidneys depending on age and sex, we carried out a transcriptome analysis using RNA sequencing (RNA-Seq) data from rat kidneys. Four differentially expressed gene (DEG) sets were generated according to age and sex, and Gene Ontology analysis and overlapping analysis of Kyoto Encyclopedia of Genes and Genomes pathways were performed for the DEG sets. Through the analysis, we revealed that inflammation- and extracellular matrix (ECM)-related genes and pathways were upregulated in both males and females during aging, which was more prominent in old males than in old females. Furthermore, quantitative real-time PCR analysis confirmed that the expression of tumor necrosis factor (TNF) signaling-related genes, Birc3, Socs3, and Tnfrsf1b, and ECM-related genes, Cd44, Col3a1, and Col5a2, which showed that the genes were markedly upregulated in males and not females during aging. Also, hematoxylin-eosin (H&E) staining for histological analysis showed that renal damage was highly shown in old males rather than old females. In conclusion, in the rat kidney, the genes involved in TNF signaling and ECM accumulation are upregulated in males more than in females during aging. These results suggest that the upregulation of the genes may have a higher contribution to age-related kidney inflammation and fibrosis in males than in females.

Hormonal Regulation of Renal Fibrosis

Fibrosis is a severe complication of many acute and chronic kidney pathologies. According to current concepts, an imbalance in the synthesis and degradation of the extracellular matrix by fibroblasts is considered the key cause of the induction and progression of fibrosis. Nevertheless, inflammation associated with the damage of tissue cells is among the factors promoting this pathological process. Most of the mechanisms accompanying fibrosis development are controlled by various hormones, which makes humoral regulation an attractive target for therapeutic intervention. In this vein, it is particularly interesting that the kidney is the source of many hormones, while other hormones regulate renal functions. The normal kidney physiology and pathogenesis of many kidney diseases are sex-dependent and thus modulated by sex hormones. Therefore, when choosing therapy, it is necessary to focus on the sex-associated characteristics of kidney functioning. In this review, we considered renal fibrosis from the point of view of vasoactive and reproductive hormone imbalance. The hormonal therapy possibilities for the treatment or prevention of kidney fibrosis are also discussed.

N-Terminal Pro-C-Type Natriuretic Peptide: The Novel Marker in Selected Disease Units

BACKGROUND

Amino-terminal pro C type natriuretic peptide (NT proCNP) is the N terminal fragment of the CNP precursor. NT proCNP occurs in an equimolar concentration with CNP in human plasma and is considered to be a marker of the extent of CNP biosynthesis. A recent study has shown associations between plasma NT proCNP and blood pressure; it is also an independent predictor of death and cardiac readmission in people with unstable angina. Beyond that, recent studies have focused on the applicability of assessing NT proCNP peptide levels in the diagnosis of diseases with different etiologies but the same denominator, i.e., inflammation.

METHODS

This study reviewed recent results on the usability of NT proCNP peptide levels in the diagnosis of diseases accompanied by statistical analysis of previously reported results.

RESULTS

The data obtained confirmed the applicability of the assessment of NT proCNP levels in biological fluids in diseases, such as Parkinson's disease, sepsis, meningitis, and asthenozoospermia.

CONCLUSION

The reported results demonstrated that NT-proCNP is helpful in a variety of diseases. Furthermore, changes in serum or CSF levels of NT-proCNP reflect only inflammatory states related to general inflammation. Local inflammation does not trigger an increase in NT proCNP level.

Prognostic Value of Urinary and Plasma C-Type Natriuretic Peptide in Acute Decompensated Heart Failure

OBJECTIVES

This study sought to characterize urinary and plasma C-type natriuretic peptide (CNP) in acute decompensated heart failure (ADHF) to define their relationship with clinical variables and to determine whether urinary and plasma CNP together add prognostic value.

BACKGROUND

CNP is a protective hormone that is synthesized in the kidney and endothelium and possesses antiremodeling properties. Urinary and plasma CNP levels are elevated in pathophysiological conditions; however, their regulation and prognostic value in heart failure (HF) is unclear.

METHODS

Urinary and plasma CNP were measured in 109 healthy subjects and 208 patients with ADHF; the 95th percentile of CNP values from healthy subjects established the normal contemporary cutoffs. Patients with ADHF were stratified based on urinary and plasma CNP levels for clinical characterization and the assessment of risk for adverse outcomes.

RESULTS

There was no significant correlation between urinary and plasma CNP in both cohorts. Urinary and plasma CNP were significantly elevated in patients with ADHF, and both increased with disease severity and were positively correlated with plasma N-terminal pro-B-type natriuretic peptide (NT-proBNP). Of the patients with ADHF, 23% had elevations in both urinary and plasma CNP, whereas 24% had normal CNP levels. During a median follow-up of 3 years, patients with elevated urinary and plasma CNP had a significantly higher risk of rehospitalization and/or death (HR: 1.79; P = 0.03) and rehospitalization (HR: 2.16; P = 0.01) after adjusting for age, sex, left ventricular ejection fraction, renal function, and plasma NT-proBNP. The C-statistic and integrated discrimination analyses further supported that the addition of urinary and plasma CNP to established risk models improved the prediction of adverse outcomes in patients with ADHF.

CONCLUSIONS

Urinary and plasma CNP are differentially regulated in ADHF, and elevations in both provided independent prognostic value for predicting adverse outcomes.

Role and mechanism of TXNIP in ageing-related renal fibrosis

Kidney ageing, which is always accompanied by renal fibrosis, drives the progression of renal fibrosis. Thioredoxin-interacting protein (TXNIP) is an endogenous suppressor of the reactive oxygen species-scavenging protein thioredoxin, which has been implicated in the ageing of some organs and is involved in renal fibrosis. However, the expression of TXNIP in ageing kidneys has not been examined, and the relationship between TXNIP and ageing-related renal fibrosis is unclear. We found that TXNIP expression was upregulated in aged mouse kidneys, and this upregulation was accompanied by ageing-related renal fibrosis phenotypes. We demonstrated that the ageing biomarkers were downregulated in TXNIP-knockout mice, and these effects resulted in the alleviation of renal fibrosis and impairments in kidney function. TXNIP overexpression in tubular cells upregulated senescence markers, promoted a profibrotic response and activated STAT3 signalling, and these parameters were inhibited by the silencing of TXNIP. Similarly, the TXNIP-mediated profibrotic response was significantly suppressed by a STAT3 inhibitor. By coimmunoprecipitation, we verified that TXNIP directly bound to STAT3, which suggested that TXNIP exacerbates renal tubular epithelial fibrosis by activating the STAT3 pathway. In summary, TXNIP plays an important role in age-related renal fibrosis and might be a therapeutic target for preventing ageing-associated renal fibrosis.

Serum Lysyl Oxidase Is a Potential Diagnostic Biomarker for Kidney Fibrosis

BACKGROUND

Kidney fibrosis is the ultimate consequence of advanced stages of chronic kidney disease (CKD); however, there are currently no reliable biomarkers or noninvasive diagnostic tests available for the detection of kidney fibrosis. Lysyl oxidase (LOX) promotes collagen cross-linking, and serum LOX levels have been shown to be elevated in patients with fibrosis of the heart, lungs, and liver. However, serum LOX levels have not been reported in patients with kidney fibrosis. We explored whether serum LOX levels are associated with kidney fibrosis.

METHOD

Overall, 202 patients with kidney disease underwent renal biopsy, scoring of kidney fibrosis, and determination of the area of kidney fibrosis. LOX levels were measured in serum and in kidney tissues. We analyzed the association of circulating LOX and tissue LOX levels with the scores and areas of kidney fibrosis. LOX expression was also investigated with in vitro and in vivo kidney fibrosis models.

RESULTS

Serum LOX levels were higher in patients with kidney fibrosis than in those without kidney fibrosis (p < 0.001) and higher in patients with moderate-severe kidney fibrosis than in patients with mild kidney fibrosis (p < 0.001). Both serum LOX and renal tissue LOX levels correlated with the area of kidney fibrosis (r = 0.748, p < 0.001; r = 0.899, p < 0.001, respectively). Receiver operating characteristic curve analysis of serum LOX levels showed an area under the curve of 0.80 (95% CI: 0.74-0.86). The optimal serum LOX level cutoff point was 253.34 pg/mL for the prediction of kidney fibrosis and 306.56 pg/mL for the prediction of moderate-severe kidney fibrosis. LOX expression levels were significantly upregulated (2.3-2.6 and 6-fold, respectively) in in vitro and in vivo interstitial fibrosis models.

CONCLUSIONS

Both serum LOX and tissue LOX levels correlated with the presence and degree of kidney fibrosis in patients with CKD. These results suggest that serum LOX levels could potentially serve as a noninvasive diagnostic biomarker for kidney fibrosis and may further potentially serve as a stratified biomarker for the identification of mild and moderate-severe kidney fibrosis.

Urinary Amino-Terminal Pro–C-Type Natriuretic Peptide: A Novel Marker of Chronic Kidney Disease in Diabetes

BACKGROUND

Chronic renal inflammation and fibrosis are common sequelae in diabetes mellitus (DM) and are major causes of premature mortality. Although upregulation of NPPC expression occurs in response to renal inflammation in experimental animals, nothing is known of the molecular forms of C-type natriuretic peptide (CNP) products in urine of people with DM or links with renal function.

METHODS

ProCNP products in urine were characterized with HPLC and a range of antisera directed to specific epitopes of amino-terminal proCNP (NTproCNP). The 5-kDa intact peptide was quantified in spot urine samples from healthy adults and 202 participants with DM selected to provide a broad range of renal function.

RESULTS

The predominant products of proCNP in urine were consistent with the 2-kDa fragment (proCNP 3–20) and a smaller peak of intact (5-kDa) fragment (proCNP 1–50, NTproCNP). No peaks consistent with bioactive forms (proCNP 82–103, 50–103) were identified. The urine NTproCNP to creatinine ratio (NCR) was more reproducible than the albumin to creatinine ratio (ACR) and strongly associated with the presence of chronic kidney disease. In models predicting independence, among 10 variables associated with renal function in DM, including plasma NTproCNP, only 3 (sex, ACR, and plasma creatinine) contributed to NCR.

CONCLUSIONS

Characterization of the products of proCNP in urine confirmed the presence of NTproCNP. In spot random urine from study participants with DM, NCR is inversely associated with estimated glomerular filtration rate. In contrast to ACR, NCR reflects nonvascular factors that likely include renal inflammation and fibrosis.

Incremental load training improves renal fibrosis by regulating the TGF‑β1/TAK1/MKK3/p38MAPK signaling pathway and inducing the activation of autophagy in aged mice

Recent studies have confirmed that kidney tissue fibrosis is closely linked to the natural aging of organs. One of its major characteristics is the reduction of autophagic activity. However, to date, few studies have assessed whether incremental load training is able to improve the occurrence of renal fibrosis caused by natural aging and the underlying mechanisms. In the present study involving male C57/BL mice, an elderly exercise group (OY group) was subjected to progressive load‑increasing rotary‑bar training (5 days/week, lasting for 6 weeks), with an elderly control group (OC group) and a young control group (YC group) used as controls. Renal fibrosis and autophagy‑associated indicators were assessed by Masson's staining, reverse transcription‑quantitative PCR analysis, western blotting, immunofluorescence and transmission electron microscopy. The results suggested that collagen deposition in the basal part of the renal tubular epithelium and glomeruli in the OY group was significantly lower than that in the OC group. In the OC group, the protein expression levels of E‑cadherin, Beclin 1 and light chain 3 were significantly decreased, and increases in α‑smooth muscle actin‑positive signals were observed in the glomerular matrix and renal capsule wall. Furthermore, the expression of transforming growth factor (TGF)‑β1 and its downstream signaling molecules TGF‑β‑activated kinase 1 (TAK1), mitogen‑activated protein kinase (MAPK) kinase (MKK3) and p38MAPK were downregulated following training. The present study confirmed that incremental load training may improve renal fibrosis in aged mice by regulating the TGF‑β1/TAK1/MMK3/p38MAPK signaling pathway and inducing the activation of autophagy to reduce the synthesis of extracellular matrix and delay the epithelial‑mesenchymal transition. The present study provides a novel experimental basis for the intervention of incremental load training to prevent senile renal fibrosis.

CRRL269

RATIONALE

Acute kidney injury (AKI) has a high prevalence and mortality in critically ill patients. It is also a powerful risk factor for heart failure incidence driven by hemodynamic changes and neurohormonal activation. However, no drugs have been approved by the Food and Drug Administration. Endogenous pGC-A (particulate guanylyl cyclase A receptor) activators were reported to preserve renal function and improve mortality in AKI patients, although hypotension accompanied by pGC-A activators have limited their therapeutic potential.

OBJECTIVE

We investigated the therapeutic potential of a nonhypotensive pGC-A activator/designer natriuretic peptide, CRRL269, in a short-term, large animal model of ischemia-induced AKI and also investigated the potential of uCNP (urinary C-type natriuretic peptide) as a biomarker for AKI.

METHODS AND RESULTS

We first showed that CRRL269 stimulated cGMP generation, suppressed plasma angiotensin II, and reduced cardiac filling pressures without lowering blood pressure in the AKI canine model. We also demonstrated that CRRL269 preserved glomerular filtration rate, increased renal blood flow, and promoted diuresis and natriuresis. Further, CRRL269 reduced kidney injury and apoptosis as evidenced by ex vivo histology and tissue apoptosis analysis. We also showed, compared with native pGC-A activators, that CRRL269 is a more potent inhibitor of apoptosis in renal cells and induced less decreases in intracellular Ca2+ concentration in vascular smooth muscle cells. The renal antiapoptotic effects were at least mediated by cGMP/PKG pathway. Further, CRRL269 inhibited proapoptotic genes expression using a polymerase chain reaction gene array. Additionally, we demonstrated that AKI increased uCNP levels.

CONCLUSIONS

Our study supports developing CRRL269 as a novel renocardiac protective agent for AKI treatment.

C53: A novel particulate guanylyl cyclase B receptor activator that has sustained activity in vivo with anti-fibrotic actions in human cardiac and renal fibroblasts

The native particulate guanylyl cyclase B receptor (pGC-B) activator, C-type natriuretic peptide (CNP), induces anti-remodeling actions in the heart and kidney through the generation of the second messenger 3', 5' cyclic guanosine monophosphate (cGMP). Indeed fibrotic remodeling, particularly in cardiorenal disease states, contributes to disease progression and thus, has been a key target for drug discovery and development. Although the pGC-B/cGMP system has been perceived as a promising anti-fibrotic pathway, its therapeutic potential is limited due to the rapid degradation and catabolism of CNP by neprilysin (NEP) and natriuretic peptide clearance receptor (NPRC). The goal of this study was to bioengineer and test in vitro and in vivo a novel pGC-B activator, C53. Here we established that C53 selectively generates cGMP via the pGC-B receptor and is highly resistant to NEP and has less interaction with NPRC in vitro. Furthermore in vivo, C53 had enhanced cGMP-generating actions that paralleled elevated plasma CNP-like levels, thus indicating a longer circulating half-life compared to CNP. Importantly in human cardiac fibroblasts (HCFs) and renal fibroblasts (HRFs), C53 exerted robust cGMP-generating actions, inhibited TGFβ-1 stimulated HCFs and HRFs proliferation chronically and suppressed the differentiation of HCFs and HRFs to myofibroblasts. The current findings advance innovation in drug discovery and highlight C53 as a novel pGC-B activator with sustained in vivo activity and anti-fibrotic actions in vitro. Future studies are warranted to explore the efficacy and therapeutic opportunity of C53 targeting fibrosis in cardiorenal disease states and beyond.

Natriuretic peptides in human heart: Novel insight into their molecular forms, functions, and diagnostic use

Among the three natriuretic peptides, atrial/A-type natriuretic peptide (ANP) and brain/B-type natriuretic peptide (BNP) are primarily produced by, and secreted from, heart tissue. They maintain cardiovascular homeostasis by binding to natriuretic peptide receptor-A. Since plasma ANP and BNP concentrations, as well as expression, are elevated in response to increased body fluid volume and pressure load on the heart wall, these peptides are widely utilized as diagnostic biomarkers for evaluating heart failure. Regardless of their high utility, differences in their molecular forms between healthy and diseased subjects and how these relate to pathophysiology have not well been examined. Recent studies have shown that the circulating molecular forms of ANP and BNP are not uniform; bioactive α-ANP is the major ANP form, whereas the weakly active proBNP is the major BNP form. The relative ratios of the different molecular forms are altered under different pathophysiological conditions. These facts indicate that detailed measurements of each form may provide useful information on the pathophysiological state of heart tissue. Here, we revisit the relationship between the molecular forms of, and pathophysiological alterations in, human ANP and BNP and discuss the possible utility of the measurement of each of the molecular forms. The third peptide, C-type natriuretic peptide, activates natriuretic peptide receptor-B, but little is known about its production and function in the heart because of its extremely low levels. However, through recent studies, its role in the heart is gradually becoming clear. Here, we summarize its molecular forms, assay systems, and functions in the heart.

Involvement of NF-κBIZ and related cytokines in age-associated renal fibrosis

Chronic inflammation is a major contributor to age-related nephropathic changes, including renal fibrosis. In this study, various experimental paradigms were designed to delineate the role played by NF-κBIZ (also known as IκBζ) in age-associated renal fibrosis. Analyses based on RNA-sequencing findings obtained by next generation sequencing (NGS) revealed the upregulations of NF-κBIZ and of IL-6 and MCP-1 (both known to be regulated by NF-κBIZ) during aging. The up-regulation of NF-κBIZ in aged rat kidneys coincided with increased macrophage infiltration. In LPS-treated macrophages, oxidative stress was found to play a pivotal role in NF-κBIZ expression, suggesting age-related oxidative stress is associated with NF-κBIZ activation. Furthermore, these in vitro findings were confirmed in LPS-treated old rats, which showed higher levels of oxidative stress and NF-κBIZ in kidneys than LPS-treated young rats. Additional in vitro experiments using macrophages and kidney fibroblasts demonstrated NF-κBIZ and related cytokines participate in fibrosis. In particular, increased levels of NF-κBIZ-associated cytokines in macrophages significantly up-regulated TGF-β induced kidney fibroblast activation. Moreover, experiments with NF-κBIZ knocked down macrophages showed reduced TGF-β-induced kidney fibroblast activation. The findings of the present study provide evidence regarding an involvement of NF-κBIZ in age-associated progressive renal fibrosis and provides potential targets for its prevention.

Impairment of PPARα and the Fatty Acid Oxidation Pathway Aggravates Renal Fibrosis during Aging

Defects in the renal fatty acid oxidation (FAO) pathway have been implicated in the development of renal fibrosis. Although, compared with young kidneys, aged kidneys show significantly increased fibrosis with impaired kidney function, the mechanisms underlying the effects of aging on renal fibrosis have not been investigated. In this study, we investigated peroxisome proliferator-activated receptor α (PPARα) and the FAO pathway as regulators of age-associated renal fibrosis. The expression of PPARα and the FAO pathway-associated proteins significantly decreased with the accumulation of lipids in the renal tubular epithelial region during aging in rats. In particular, decreased PPARα protein expression associated with increased expression of PPARα-targeting microRNAs. Among the microRNAs with increased expression during aging, miR-21 efficiently decreased PPARα expression and impaired FAO when ectopically expressed in renal epithelial cells. In cells pretreated with oleic acid to induce lipid stress, miR-21 treatment further enhanced lipid accumulation. Furthermore, treatment with miR-21 significantly exacerbated the TGF-β-induced fibroblast phenotype of epithelial cells. We verified the physiologic importance of our findings in a calorie restriction model. Calorie restriction rescued the impaired FAO pathway during aging and slowed fibrosis development. Finally, compared with kidneys of aged littermate controls, kidneys of aged PPARα^-/- mice showed exaggerated lipid accumulation, with decreased activity of the FAO pathway and a severe fibrosis phenotype. Our results suggest that impaired renal PPARα signaling during aging aggravates renal fibrosis development, and targeting PPARα is useful for preventing age-associated CKD.

MMP2-A2M interaction increases ECM accumulation in aged rat kidney and its modulation by calorie restriction

Age-associated renal fibrosis is related with renal function decline during aging. Imbalance between accumulation and degradation of extracellular matrix is key feature of fibrosis. In this study, RNA-sequencing (RNA-Seq) results based on next-generation sequencing (NGS) data were analyzed to identify key proteins that change during aging and calorie restriction (CR). Among the changed genes, A2M and MMP2, which are known to interact, exhibited the highest between centrality (BC) and degree values when analyzed by protein–protein interaction (PPI). Both mRNA and protein levels of MMP2 and A2M were increased during aging. Furthermore, the interaction between MMP2 and A2M was verified by immunoprecipitation and immunohistochemistry. MMP2 activity was further measured under the presence or absence of A2M-MMP2 interaction. MMP2 activity, which was increased under the absence of A2M-MMP2 interaction, was significantly decreased under the presence of interactions in aged kidney. We further hypothesized that the interaction between A2M-MMP2 played a role in the inactivation of MMP2 leading to accumulation of ECM including collagen type I and IV. Aged kidney showed highly accumulated MMP2 substrate proteins despite of increased MMP2 protein expression and CR blunted these accumulation. Additional in vivo analysis revealed that the signal transducer and activator of transcription (STAT) 3 transcriptional factor was significantly increased thus increasing A2M expression during aging. STAT3 activating cytokines were also highly increased in aged kidney. In conclusion, the results of the present study indicate that A2M-MMP2 interaction has a role in age-associated renal ECM accumulation and in the suppression such fibrosis by CR.

Cardiac fibrosis in the ageing heart: Contributors and mechanisms

Cardiac fibrosis refers to an excessive deposition of extracellular matrix (ECM) in cardiac tissue. Fibrotic tissue is stiffer and less compliant, resulting in subsequent cardiac dysfunction and heart failure. Cardiac fibrosis in the ageing heart may involve activation of fibrogenic signalling and inhibition of anti-fibrotic signalling, leading to an imbalance of ECM turnover. Excessive accumulation of ECM such as collagen in older patients contributes to progressive ventricular dysfunction. Overexpression of collagen is derived from various sources, including higher levels of fibrogenic growth factors, proliferation of fibroblasts and cellular transdifferentiation. These may be triggered by factors, such as oxidative stress, inflammation, hypertension, cellular senescence and cell death, contributing to age-related fibrotic cardiac remodelling. In this review, we will discuss the fibrogenic contributors in age-related cardiac fibrosis, and the potential mechanisms by which fibrogenic processes can be interrupted for therapeutic intent.

Early activation of deleterious molecular pathways in the kidney in experimental heart failure with atrial remodeling

Heart failure (HF) is a major health problem with worsening outcomes when renal impairment is present. Therapeutics for early phase HF may be effective for cardiorenal protection, however the detailed characteristics of the kidney in early‐stage HF (ES‐HF), and therefore treatment for potential renal protection, are poorly defined. We sought to determine the gene and protein expression profiles of specific maladaptive pathways of ES‐HF in the kidney and heart. Experimental canine ES‐HF, characterized by de‐novo HF with atrial remodeling but not ventricular fibrosis, was induced by right ventricular pacing for 10 days. Kidney cortex (KC), medulla (KM), left ventricle (LV), and left atrial (LA) tissues from ES‐HF versus normal canines (n = 4 of each) were analyzed using RT‐PCR microarrays and protein assays to assess genes and proteins related to inflammation, renal injury, apoptosis, and fibrosis. ES‐HF was characterized by increased circulating natriuretic peptides and components of the renin‐angiotensin‐aldosterone system and decreased sodium and water excretion with mild renal injury and up‐regulation of CNP and renin genes in the kidney. Compared to normals, widespread genes, especially genes of the inflammatory pathways, were up‐regulated in KC similar to increases seen in LA. Protein expressions related to inflammatory cytokines were also augmented in the KC. Gene and protein changes were less prominent in the LV and KM. The ES‐HF displayed mild renal injury with widespread gene changes and increased inflammatory cytokines. These changes may provide important clues into the pathophysiology of ES‐HF and for therapeutic molecular targets in the kidney of ES‐HF.

Urinary C-type natriuretic peptide excretion: a promising biomarker to detect underlying renal injury and remodeling both acutely and chronically

Acute kidney injury (AKI) refers to a sudden decline in renal function. A growing body of evidence demonstrates that AKI is a risk factor for the future development or accelerated progression of chronic kidney disease (CKD), whereas the actual distinction between AKI and CKD remains unknown. CNP is predominantly present in the kidney and possesses multiple renoprotective properties. Urinary CNP excretion tends to be high in AKI, whereas back to the baseline in CKD. The dynamic changes in urinary CNP excretion may help detect underlying renal injury and remodeling both acutely and chronically.

Cardiorenal fibrosis and dysfunction in aging: Imbalance in mediators and regulators of collagen

Cardiorenal fibrosis is a biological process that increases with age and contributes to dysfunction of the heart and kidney. While numerous circulating and tissue hormones, cytokines and enzymes have been identified in the development of cardiorenal fibrosis, several reports have suggested that the anti-fibrotic natriuretic peptide system (NPS), pro-fibrotic renin-angiotensin-aldosterone system (RAAS), transforming growth factor-beta 1 (TGF-β1), matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases (TIMPs) are fundamental regulators and mediators of this process. However, the simultaneous assessment of these components in the development of age-mediated cardiorenal fibrotic remodeling is not completely understood. Thus, we assessed cardiorenal structure and function, the circulating NPS and RAAS and the cardiorenal tissue gene expression of collagen (Col) I, Col III, TGF-β1, MMP-9 and TIMP-1 in 2 and 20 month old Fischer rats. Our studies determined that aging was characterized by an increase in cardiorenal fibrosis that was accompanied with cardiorenal dysfunction. These alterations were associated with lower circulating atrial and C-type natriuretic peptides and higher angiotensin II and aldosterone levels in the aged rats. Moreover, we observed a decrease in Col I and III and an increase in TIMP- mRNA expressions in the aged heart and kidney, while TGF-β1 expression increased and MMP-9 decreased only in the aged kidney. We conclude that the age-mediated alterations in these fibrotic regulator and mediator profiles favors collagen accumulation due to an imbalance between the NPS and RAAS as well as a decline in the degradative pathway, thus suggesting a therapeutic opportunity to target these components.

Protective effects of C-type natriuretic peptide on cisplatin-induced nephrotoxicity in mice

PURPOSE

Cisplatin is a highly effective chemotherapeutic agent used to treat various malignancies, but its utility is compromised by its nephrotoxicity. C-type natriuretic peptide (CNP), a member of the natriuretic peptide family, exhibits anti-inflammatory effects by activating its specific receptor, guanylyl cyclase (GC)-B. CNP and GC-B receptor are known to be expressed in both the vascular endothelium and the kidney. The objective of this study was to investigate the renoprotective effects of CNP in a mouse model of cisplatin-induced nephrotoxicity.

METHODS

C57BL/6 mice were divided into three groups: normal control mice; cisplatin (20 mg/kg, intraperitoneal) mice treated with vehicle; and cisplatin mice treated with CNP (2.5 µg/kg/min, subcutaneous). At 72 h after cisplatin injection, urine, blood and kidney samples were collected. Urine and blood samples were examined biochemically. Histological findings and gene expression in kidney tissue were evaluated.

RESULTS

CNP reduced histological renal tubular damage and apoptosis induced by cisplatin and suppressed plasma blood urea nitrogen and creatinine levels, which were elevated by cisplatin administration. CNP treatment decreased the expression of kidney injury molecule-1 and monocyte chemoattractant protein-1, which were elevated in the kidney by cisplatin administration. CNP treatment attenuated the decrease in GC-B expression in cisplatin-induced kidney injury.

CONCLUSIONS

The present study is the first to show that CNP inhibits nephrotoxicity and kidney cell damage induced by cisplatin. The mechanism of action may involve down-regulation of inflammatory cytokine expression in cisplatin-induced kidney injury and attenuation of apoptosis in renal tubular cells.

Urinary C-type natriuretic peptide: an emerging biomarker for heart failure and renal remodeling

The public health and economic burden of heart failure (HF) is staggering and the need for relevant pathophysiologic and clinical biomarkers to advance the field and improve HF therapy remains high. Renal dysfunction is common among HF patients and is associated with increased HF hospitalization and mortality. It is widely recognized that mechanisms contributing to HF pathogenesis include a complex bidirectional interaction between the kidney and heart, encompassed by the term cardiorenal syndrome (CRS). Among a new wave of urinary biomarkers germane to CRS, C-type natriuretic peptide (CNP) has emerged as an innovative biomarker of renal structural and functional impairment in HF and chronic renal disease states. CNP is a hormone, synthesized in the kidney, and is an important regulator of cell proliferation and organ fibrosis. Hypoxia, cytokines and fibrotic growth factors, which are inherent to both cardiac and renal remodeling processes, are among the recognized stimuli for CNP production and release. In this review we aim to highlight current knowledge regarding the biology and pathophysiological correlates of urinary CNP, and its potential clinical utility as a diagnostic and prognostic biomarker in HF and renal disease states.

miR-195 regulates SIRT1-mediated changes in diabetic retinopathy

AIMS/HYPOTHESIS

Endothelial cell (EC) damage is a key mechanism causing retinal microvascular injury in diabetes. Several microRNAs (miRNAs) have been found to regulate sirtuin 1 (SIRT1, which is involved in regulation of the cell cycle, survival and metabolism) in various tissues and disease states, but no studies have been conducted on the role of miRNA in regulation of SIRT1 in diabetic retinopathy. Here we investigated the effect of miRNA-195 (miR-195), a SIRT1-targeting miRNA, on the development of diabetes-induced changes in ECs and retina.

METHODS

The level of miR-195 was measured in human retinal and dermal microvascular ECs (HRECs, HMECs) following exposure to 25 mmol/l glucose (high glucose, HG) and 5 mmol/l glucose (normal glucose, NG). SIRT1 and fibronectin levels were examined following transfection with miR-195 mimic or antagomir or forced expression of SIRT1. Retinal tissues from diabetic rats were similarly studied following intravitreal injection of an miR-195 antagomir or mimic. In situ hybridisation was used to localise retinal miR-195.

RESULTS

HG caused increased miR-195 levels and decreased SIRT1 expression (compared with NG) in both HRECs and HMECs. Transfection with miR-195 antagomir and forced expression of SIRT1 prevented such changes, whereas transfection with miR-195 mimic produced HG-like effects. A luciferase assay confirmed the binding of miR-195 to the 3' untranslated region of SIRT1. miR-195 expression was upregulated in retinas of diabetic rats and intravitreal injection of miR-195 antagomir ameliorated levels of SIRT1.

CONCLUSIONS/INTERPRETATION

These studies identified a novel mechanism whereby miR-195 regulates SIRT1-mediated tissue damage in diabetic retinopathy.

Urinary C-type natriuretic peptide: a new heart failure biomarker

OBJECTIVES

This study was conducted to determine whether urinary excretion of C-type natriuretic peptide (CNP) is elevated in acute decompensated heart failure (ADHF) and whether elevated levels predict adverse outcomes.

BACKGROUND

Urinary CNP has been detected in patients with heart failure, but its clinical significance and prognostic utility, compared to established kidney injury biomarkers, in ADHF is unknown.

METHODS

We measured 24-h urinary excretion and concurrent plasma concentrations of CNP22, CNP53, and NT-CNP53 in 58 ADHF patients and 20 healthy control subjects. Urinary kidney injury molecule (KIM)-1 and neutrophil gelatinase–associated lipocalin (NGAL) and plasma N-terminal pro-B type natriuretic peptide (NT-proBNP) were also measured. Mortality and all-cause rehospitalization/death were assessed over a follow-up of 1.5 ± 0.9 years.

RESULTS

ADHF patients had higher urinary excretion of all 3 CNP molecular forms than did controls. Plasma CNP22 and CNP53 were elevated in ADHF but showed limited correlation with urinary excretion, suggesting that mainly renal-derived CNP appears in urine. Plasma NT-proBNP and urinary KIM-1 were also elevated in ADHF (p < 0.0001); urinary NGAL was similar to that in controls. At 6 months, event-free survival values in ADHF patients were 86% for mortality and 59% for all-cause rehospitalization/death. On Cox regression analysis, urinary NT-CNP53 was the only predictor of mortality (hazard ratio: 1.7; 95% confidence interval: 1.1 to 2.4; p = 0.01) and all-cause rehospitalization/death (hazard ratio: 1.8; 95% confidence interval: 1.3 to 2.4; p = 0.0004), even after adjustment. Integrated discrimination analysis suggested that urinary NT-CNP53 combined with plasma NT-proBNP improved the prediction of adverse outcomes.

CONCLUSIONS

The findings from this study support the clinical utility of urinary CNP molecular forms. In ADHF, urinary NT-CNP53 correlated with prognosis, better predicted outcomes than did urinary NGAL and KIM-1, and improved the prognostic value of plasma NT-proBNP.

High glucose induced alteration of SIRTs in endothelial cells causes rapid aging in a p300 and FOXO regulated pathway

In diabetes, some of the cellular changes are similar to aging. We hypothesized that hyperglycemia accelerates aging-like changes in the endothelial cells (ECs) and tissues leading to structural and functional damage. We investigated glucose-induced aging in 3 types of ECs using senescence associated β-gal (SA β-gal) staining and cell morphology. Alterations of sirtuins (SIRTs) and their downstream mediator FOXO and oxidative stress were investigated. Relationship of such alteration with histone acetylase (HAT) p300 was examined. Similar examinations were performed in tissues of diabetic animals. ECs in high glucose (HG) showed evidence of early senescence as demonstrated by increased SA β-gal positivity and reduced replicative capacities. These alterations were pronounced in microvascular ECs. They developed an irregular and hypertrophic phenotype. Such changes were associated with decreased SIRT (1–7) mRNA expressions. We also found that p300 and SIRT1 regulate each other in such process, as silencing one led to increase of the others’ expression. Furthermore, HG caused reduction in FOXO1’s DNA binding ability and antioxidant target gene expressions. Chemically induced increased SIRT1 activity and p300 knockdown corrected these abnormalities slowing aging-like changes. Diabetic animals showed increased cellular senescence in renal glomerulus and retinal blood vessels along with reduced SIRT1 mRNA expressions in these tissues. Data from this study demonstrated that hyperglycemia accelerates aging-like process in the vascular ECs and such process is mediated via downregulation of SIRT1, causing reduction of mitochondrial antioxidant enzyme in a p300 and FOXO1 mediated pathway.

CD-NP: a novel engineered dual guanylyl cyclase activator with anti-fibrotic actions in the heart

Natriuretic peptides (NPs) are cardioprotective through the activation of guanylyl cyclase (GC) receptors A and B. CD-NP, also known as cenderitide, is a novel engineered NP that was designed to uniquely serve as a first-in-class dual GC receptor agonist. Recognizing the aldosterone suppressing actions of GC-A activation and the potent inhibitory actions on collagen synthesis and fibroblast proliferation through GC-B activation, the current study was designed to establish the anti-fibrotic actions of CD-NP, administered subcutaneously, in an experimental rat model of early cardiac fibrosis induced by unilateral nephrectomy (UNX). Our results demonstrate that a two week subcutaneous infusion of CD-NP significantly suppresses left ventricular fibrosis and circulating aldosterone, while preserving both systolic and diastolic function, in UNX rats compared to vehicle treated UNX rats. Additionally we also confirmed, in vitro, that CD-NP significantly generates the second messenger, cGMP, through both the GC-A and GC-B receptors. Taken together, this novel dual GC receptor activator may represent an innovative anti-fibrotic therapeutic agent.

Overexpressed C-type natriuretic peptide serves as an early compensatory response to counteract extracellular matrix remodeling in unilateral ureteral obstruction rats

Although the mechanism underlying C-type natriuretic peptide (CNP) beneficial effects is not entirely understood, modulating the expression of matrix metalloproteinases (MMPs)/tissue inhibitors of metalloproteinases (TIMPs) may play an important role. The study presented herein was designed as a first demonstration of the regulative effects of CNP on MMPs/TIMPs expression in unilateral ureteral obstruction (UUO) rats. The continuous changes of CNP, MMP-2, MMP-9, TIMP-1, TIMP-2 and type IV collagen (Col-IV) expression were determined in the obstructed rat kidneys at 3 days, 1, 2, and 3 months post-UUO respectively. According to the real-time PCR analysis, CNP, MMP-2 and MMP-9 mRNA expression in the obstructed kidneys were significantly higher compared to every time corresponding SOR, and progressively decreased over time. In contrast, in the obstructed kidneys collected 2 and 3 months post-UUO, the higher TIMP-1 and TIMP-2 mRNA expression were observed in comparison to the corresponding SOR group. The above trends of CNP, MMP-2, MMP-9, TIMP-1, and TIMP-2 transcripts were confirmed by their protein expression based on immunohistochemistry and western blot, and finally contributed to the progressive elevated Col-IV expression in the obstructed kidneys throughout the entire study period. Overexpressed CNP may be an early compensatory response to counteract extracellular matrix remodeling in UUO rats.