Current epigenetic aspects the clinical kidney researcher should embrace

Chronic kidney disease (CKD), affecting 10-12% of the world's adult population, is associated with a considerably elevated risk of serious comorbidities, in particular, premature vascular disease and death. Although a wide spectrum of causative factors has been identified and/or suggested, there is still a large gap of knowledge regarding the underlying mechanisms and the complexity of the CKD phenotype. Epigenetic factors, which calibrate the genetic code, are emerging as important players in the CKD-associated pathophysiology. In this article, we review some of the current knowledge on epigenetic modifications and aspects on their role in the perturbed uraemic milieu, as well as the prospect of applying epigenotype-based diagnostics and preventive and therapeutic tools of clinical relevance to CKD patients. The practical realization of such a paradigm will require that researchers apply a holistic approach, including the full spectrum of the epigenetic landscape as well as the variability between and within tissues in the uraemic milieu

Early vascular ageing and cellular senescence in chronic kidney disease

Chronic kidney disease (CKD) is a clinical model of premature ageing characterized by progressive vascular dis- ease, systemic inflammation, muscle wasting and frailty. The predominant early vascular ageing (EVA) process mediated by medial vascular calcification (VC) results in a marked discrepancy between chronological and bio- logical vascular age in CKD. Though the exact underlying mechanisms of VC and EVA are not fully elucidated, ac- cumulating evidence indicates that cellular senescence - and subsequent chronic inflammation through the senescence-associated secretary phenotype (SASP) - plays a fundamental role in its initiation and progression. In this review, we discuss the pathophysiological links between senescence and the EVA process in CKD, with focus on cellular senescence and media VC, and potential anti-ageing therapeutic strategies of senolytic drugs targeting cellular senescence and EVA in CKD.Swedish Research Council (grant no 2009-1068)European Union‘s Horizon 2020 research and innovation Program, Marie Skłodowska-Curie (grant agreement No 722609)International Network for Training on Risks of Vascular Intimal Calcification and roads to Regression of Cardiovascular Disease (INTRICARE)Baxter HealthcarePublishe

CDKN2A/p16INK4a expression is associated with vascular progeria in chronic kidney disease

Patients with chronic kidney disease (CKD) display a progeric vascular phenotype linked to apoptosis, cellular senescence and osteogenic transformation. This has proven intractable to modelling appropriately in model organisms. We have therefore investigated this directly in man, using for the first time validated cellular biomarkers of ageing (CDKN2A/p16INK4a, SA-β-Gal) in arterial biopsies from 61 CKD patients undergoing living donor renal transplantation. We demonstrate that in the uremic milieu, increased arterial expression of CDKN2A/p16INK4a associated with vascular progeria in CKD, independently of chronological age. The arterial expression of CDKN2A/p16INK4a was significantly higher in patients with coronary calcification (p=0.01) and associated cardiovascular disease (CVD) (p=0.004). The correlation between CDKN2A/p16INK4a and media calcification was statistically significant (p=0.0003) after correction for chronological age. We further employed correlate expression of matrix Gla protein (MGP) and runt-related transcription factor 2 (RUNX2) as additional pathognomonic markers. Higher expression of CDKN2A/p16INK4a, RUNX2 and MGP were observed in arteries with severe media calcification. The number of p16INK4a and SA-β-Gal positive cells was higher in biopsies with severe media calcification. A strong inverse correlation was observed between CDKN2A/p16INK4a expression and carboxylated osteocalcin levels. Thus, impaired vitamin K mediated carboxylation may contribute to premature vascular senescence

Inflammation and premature ageing in chronic kidney disease

Persistent low-grade inflammation and premature ageing are hallmarks of the uremic phenotype and contribute to impaired health status, reduced quality of life, and premature mortality in chronic kidney disease (CKD). Because there is a huge global burden of disease due to CKD, treatment strategies targeting inflammation and premature ageing in CKD are of particular interest. Several distinct features of the uremic phenotype may represent potential treatment options to attenuate the risk of progression and poor outcome in CKD. The nuclear factor erythroid 2-related factor 2 (NRF2)−kelch-like erythroid cell-derived protein with CNC homology [ECH]-associated protein 1 (KEAP1) signaling pathway, the endocrine phosphate-fibroblast growth factor-23−klotho axis, increased cellular senescence, and impaired mitochondrial biogenesis are currently the most promising candidates, and different pharmaceutical compounds are already under evaluation. If studies in humans show beneficial effects, carefully phenotyped patients with CKD can benefit from them

CDKN2A/p16INK4a expression is associated with vascular progeria in chronic kidney disease

Patients with chronic kidney disease (CKD) display a progeric vascular phenotype linked to apoptosis, cellular senescence and osteogenic transformation. This has proven intractable to modelling appropriately in model organisms. We have therefore investigated this directly in man, using for the first time validated cellular biomarkers of ageing (CDKN2A/p16INK4a, SA-β-Gal) in arterial biopsies from 61 CKD patients undergoing living donor renal transplantation. We demonstrate that in the uremic milieu, increased arterial expression of CDKN2A/p16INK4a associated with vascular progeria in CKD, independently of chronological age. The arterial expression of CDKN2A/p16INK4a was significantly higher in patients with coronary calcification (p=0.01) and associated cardiovascular disease (CVD) (p=0.004). The correlation between CDKN2A/p16INK4a and media calcification was statistically significant (p=0.0003) after correction for chronological age. We further employed correlate expression of matrix Gla protein (MGP) and runt-related transcription factor 2 (RUNX2) as additional pathognomonic markers. Higher expression of CDKN2A/p16INK4a, RUNX2 and MGP were observed in arteries with severe media calcification. The number of p16INK4a and SA-β-Gal positive cells was higher in biopsies with severe media calcification. A strong inverse correlation was observed between CDKN2A/p16INK4a expression and carboxylated osteocalcin levels. Thus, impaired vitamin K mediated carboxylation may contribute to premature vascular senescence

Longitudinal genome-wide DNA methylation changes in response to kidney failure replacement therapy

Chronic kidney disease (CKD) is an emerging public health priority associated with high mortality rates and demanding treatment regimens, including life-style changes, medications or even dialysis or renal transplantation. Unavoidably, the uremic milieu disturbs homeostatic processes such as DNA methylation and other vital gene regulatory mechanisms. Here, we aimed to investigate how dialysis or kidney transplantation modifies the epigenome-wide methylation signature over 12 months of treatment. We used the Infinium HumanMethylation450 BeadChip on whole blood samples from CKD-patients undergoing either dialysis (n = 11) or kidney transplantation (n = 12) and 24 age- and sex-matched population-based controls. At baseline, comparison between patients and controls identified several significant (PFDR < 0.01) CpG methylation differences in genes with functions relevant to inflammation, cellular ageing and vascular calcification. Following 12 months, the global DNA methylation pattern of patients approached that seen in the control group. Notably, 413 CpG sites remained differentially methylated at follow-up in both treatment groups compared to controls. Together, these data indicate that the uremic milieu drives genome-wide methylation changes that are partially reversed with kidney failure replacement therapy. Differentially methylated CpG sites unaffected by treatment may be of particular interest as they could highlight candidate genes for kidney disease per se

Phosphatidylserine Targets Single-Walled Carbon Nanotubes to Professional Phagocytes In Vitro and In Vivo

Broad applications of single-walled carbon nanotubes (SWCNT) dictate the necessity to better understand their health effects. Poor recognition of non-functionalized SWCNT by phagocytes is prohibitive towards controlling their biological action. We report that SWCNT coating with a phospholipid “eat-me” signal, phosphatidylserine (PS), makes them recognizable in vitro by different phagocytic cells - murine RAW264.7 macrophages, primary monocyte-derived human macrophages, dendritic cells, and rat brain microglia. Macrophage uptake of PS-coated nanotubes was suppressed by the PS-binding protein, Annexin V, and endocytosis inhibitors, and changed the pattern of pro- and anti-inflammatory cytokine secretion. Loading of PS-coated SWCNT with pro-apoptotic cargo (cytochrome c) allowed for the targeted killing of RAW264.7 macrophages. In vivo aspiration of PS-coated SWCNT stimulated their uptake by lung alveolar macrophages in mice. Thus, PS-coating can be utilized for targeted delivery of SWCNT with specified cargoes into professional phagocytes, hence for therapeutic regulation of specific populations of immune-competent cells

Expression of inflammatory and insulin signaling genes in acute and chronic stress

The acute surgical stress response induces a short-term inflammatory and insulin resistant condition, commonly producing hyperglycemia, which is strongly associated to morbidity and mortality in postsurgical patients. The chronic state of renal insufficiency, on the other hand, represents a long-term stress associated with alarmingly high mortality rates, primarily due to cardiovascular complications, and is similarly related to chronic inflammation, oxidative stress, and insulin resistance. The underlying mechanisms are however incompletely understood. A growing wealth of data emphasizes how mutual relationships between immunity and metabolism may contribute to disease, as well as the intrinsic properties of metabolically active organs, such as adipose tissue and skeletal muscle. Hence, in this translational study, we aimed to identify inflammatory and metabolic mediators being dysregulated and potentially contributing to homeostatic disturbances after surgery and in chronic kidney disease (CKD) patients. In paper I, we evaluated the expression changes of 45 inflammatory and insulin signaling genes in skeletal muscle during major abdominal surgery of eight non-diabetic patients. In paper II, mRNA measurements of 21 genes were performed in 12 patients undergoing surgery on two separate adipose tissue depots: abdominal subcutaneous and omental adipose tissue. Overall, although some tissue specific alterations were observed, striking similarities were noted between the tissues. For example, we observed significantly increased mRNA levels of inflammatory signaling genes (e.g. interleukin 6 (IL6), suppressor of cytokine signaling 3 (SOCS3) and nicotinamide phosphoribosyltransferase (NAMPT)) in all tissues examined, but tumor necrosis factor (TNF) was only up-regulated in skeletal muscle. Insulin signaling pathway genes (e.g. insulin receptor substrate 1 (IRS1) and glucose transporter 4 (SLC2A4)), were only significantly affected in the adipose tissue depots. Paper III and IV focused on abdominal subcutaneous adipose tissue. Gene expression levels were compared between CKD stage 5 patients and non-uremic controls to reveal uremic specific alterations. In accordance with surgical patients, adipose tissue from CKD patients showed a significant up-regulation of inflammatory pathway genes such as IL6 and SOCS3. Additionally, leptin and the oxidative stress-related genes uncoupling protein-2 (UCP2) and cytochrome b-245, alpha polypeptide (CYBA) were found to be down-regulated in relation to controls. Interestingly, we found reduced mRNA levels of the bone-associated factor osteoprotegerin (OPG), with reported implications for inflammation, vascular diseases and mortality, in uremic adipose tissue as compared to control tissue, despite higher OPG serum protein concentrations in patients and no apparent immunohistochemical differences. These observations suggest that aberrant gene expression of inflammatory and oxidative stress genes, as well as genes implicated in the control of vascular calcification, may be important features of the uremic adipose tissue, which may have significant effects on the uremic phenotype. In summary, these studies contribute to our understanding of human gene expression alterations in association to clinical conditions producing acute and chronic stress, respectively, which may have implications for inflammatory and metabolic complications observed after surgery and in CKD. These results may also be relevant for other disorders in which pronounced inflammation and metabolic disturbances exacerbate the disease state, such as obesity and diabetes

Inflammation and oxidative stress in CKD and dialysis patients

Significance: Chronic kidney disease (CKD) can be regarded as a burden of lifestyle disease that shares common underpinning features and risk factors with the ageing process; a complex constituted by several adverse components, including chronic inflammation, oxidative stress, early vascular ageing and cellular senescence. Recent Advances: A systemic approach to tackle CKD, based on mitigating the associated inflammatory, cell stress and damage processes, has the potential to attenuate the effects of CKD, but also pre-empts the development and progression of associated morbidities. In effect, this will enhance health span and compress the period of morbidity. Pharmacological, nutritional and potentially lifestyle-based interventions are promising therapeutic avenues to achieve such a goal. Critical Issues: In the present review, currents concepts of inflammation and oxidative damage as key pathomechanisms in CKD are addressed. In particular, potential beneficial but also adverse effects of different systemic interventions in patients with CKD are discussed. Future Directions: Senotherapeutics, the NRF2–KEAP1 signaling pathway, the endocrine klotho axis, inhibitors of the sodium–glucose cotransporter 2 (SGLT2), and live bio-therapeutics have the potential to reduce the burden of CKD and improve quality of life, as well as morbidity and mortality, in this fragile high-risk patient group

The G-protein coupled receptor ChemR23 determines smooth muscle cell phenotypic switching to enhance high phosphate-induced vascular calcification

AIMS: Vascular calcification, a marker of increased cardiovascular risk, is an active process orchestrated by smooth muscle cells. Observational studies indicate that omega-3 fatty acids protect against vascular calcification, but the mechanisms are unknown. The G-protein coupled receptor ChemR23 transduces the resolution of inflammation induced by the omega-3-derived lipid mediator resolvin E1. ChemR23 also contributes to osteoblastic differentiation of stem cells and bone formation, but its role in vascular calcification is unknown. The aim of this study was to establish the role of ChemR23 in smooth muscle cell fate and calcification. METHODS AND RESULTS: Gene expression analysis in epigastric arteries derived from patients with chronic kidney disease and vascular calcification revealed that ChemR23 mRNA levels predicted a synthetic smooth muscle cell phenotype. Genetic deletion of ChemR23 in mice prevented smooth muscle cell de-differentiation. ChemR23-deficient smooth muscle cells maintained a non-synthetic phenotype and exhibited resistance to phosphate-induced calcification. Moreover, ChemR23-deficient mice were protected against vitamin D3-induced vascular calcification. Resolvin E1 inhibited smooth muscle cell calcification through ChemR23. Introduction of the Caenorhabditis elegans Fat1 transgene, leading to an endogenous omega-3 fatty acid synthesis and hence increased substrate for resolvin E1 formation, significantly diminished the differences in phosphate-induced calcification between ChemR23+/+ and ChemR23-/- mice. CONCLUSION: This study identifies ChemR23 as a previously unrecognized determinant of synthetic and osteoblastic smooth muscle cell phenotype, favouring phosphate-induced vascular calcification. This effect may be of particular importance in the absence of ChemR23 ligands, such as resolvin E1, which acts as a calcification inhibitor under hyperphosphatic conditions