Promoter methylation is associated with the age-dependent loss of N-cadherin in the rat kidney

Multi-omic analysis of mandibuloacral dysplasia type A patient iPSC-derived MSC senescence reveals miR-311 as a novel biomarker for MSC senescence

Mandibuloacral dysplasia type A (MADA) is a rare genetic progeroid syndrome associated with lamin A/C (LMNA) mutations. Pathogenic mutations of LMNA result in nuclear structural abnormalities, mesenchymal tissue damage and progeria phenotypes. However, it remains elusive how LMNA mutations cause mesenchymal-derived cell senescence and disease development. Here, we established an in vitro senescence model using induced pluripotent stem cell-derived mesenchymal stem cells (iMSCs) from MADA patients with homozygous LMNA p.R527C mutation. When expanded to passage 13 in vitro, R527C iMSCs exhibited marked senescence and attenuation of stemness potential, accompanied by immunophenotypic changes. Transcriptome and proteome analysis revealed that cell cycle, DNA replication, cell adhesion and inflammation might play important roles in senescence. In-depth evaluation of changes in extracellular vesicle (EV) derived iMSCs during senescence revealed that R527C iMSC-EVs could promote surrounding cell senescence by carrying pro-senescence microRNAs (miRNAs), including a novel miRNA called miR-311, which can serve as a new indicator for detecting chronic and acute mesenchymal stem cell (MSC) senescence and play a role in promoting senescence. Overall, this study advanced our understanding of the impact of LMNA mutations on MSC senescence and provided novel insights into MADA therapy as well as the link between chronic inflammation and aging development.

Population Epigenetics: The Extent of DNA Methylation Variation in Wild Animal Populations

Population epigenetics explores the extent of epigenetic variation and its dynamics in natural populations encountering changing environmental conditions. In contrast to population genetics, the basic concepts of this field are still in their early stages, especially in animal populations. Epigenetic variation may play a crucial role in phenotypic plasticity and local adaptation as it can be affected by the environment, it is likely to have higher spontaneous mutation rate than nucleotide sequences do, and it may be inherited via non-mendelian processes. In this review, we aim to bring together natural animal population epigenetic studies to generate new insights into ecological epigenetics and its evolutionary implications. We first provide an overview of the extent of DNA methylation variation and its autonomy from genetic variation in wild animal population. Second, we discuss DNA methylation dynamics which create observed epigenetic population structures by including basic population genetics processes. Then, we highlight the relevance of DNA methylation variation as an evolutionary mechanism in the extended evolutionary synthesis. Finally, we suggest new research directions by highlighting gaps in the knowledge of the population epigenetics field. As for our results, DNA methylation diversity was found to reveal parameters that can be used to characterize natural animal populations. Some concepts of population genetics dynamics can be applied to explain the observed epigenetic structure in natural animal populations. The set of recent advancements in ecological epigenetics, especially in transgenerational epigenetic inheritance in wild animal population, might reshape the way ecologists generate predictive models of the capacity of organisms to adapt to changing environments.

A transcriptomic analysis of serial-cultured, tonsil-derived mesenchymal stem cells reveals decreased integrin α3 protein as a potential biomarker of senescent cells

Background

Mesenchymal stem cells (MSCs) have been widely used for stem cell therapy, and serial passage of stem cells is often required to obtain sufficient cell numbers for practical applications in regenerative medicine. A long-term serial cell expansion can potentially induce replicative senescence, which leads to a progressive decline in stem cell function and stemness, losing multipotent characteristics. To improve the therapeutic efficiency of stem cell therapy, it would be important to identify specific biomarkers for senescent cells.

Methods

Tonsil-derived mesenchymal stem cells (TMSCs) with 20–25 passages were designated as culture-aged TMSCs, and their mesodermal differentiation potentials as well as markers of senescence and stemness were compared with the control TMSCs passaged up to 8 times at the most (designated as young). A whole-genome analysis was used to identify novel regulatory factors that distinguish between the culture-aged and control TMSCs. The identified markers of replicative senescence were validated using Western blot analyses.

Results

The culture-aged TMSCs showed longer doubling time compared to control TMSCs and had higher expression of senescence-associated (SA)-β-gal staining but lower expression of the stemness protein markers, including Nanog, Oct4, and Sox2 with decreased adipogenic, osteogenic, and chondrogenic differentiation potentials. Microarray analyses identified a total of 18,614 differentially expressed genes between the culture-aged and control TMSCs. The differentially expressed genes were classified into the Gene Ontology categories of cellular component (CC), functional component (FC), and biological process (BP) using KEGG (Kyoto encyclopedia of genes and genomes) pathway analysis. This analysis revealed that those genes associated with CC and BP showed the most significant difference between the culture-aged and control TMSCs. The genes related to extracellular matrix-receptor interactions were also shown to be significantly different (p < 0.001). We also found that culture-aged TMSCs had decreased expressions of integrin α3 (ITGA3) and phosphorylated AKT protein (p-AKT-Ser⁴⁷³) compared to the control TMSCs.

Conclusions

Our data suggest that activation of ECM-receptor signaling, specifically involved with integrin family-mediated activation of the intracellular cell survival-signaling molecule AKT, can regulate stem cell senescence in TMSCs. Among these identified factors, ITGA3 was found to be a representative biomarker of the senescent TMSCs. Exclusion of the TMSCs with the senescent TMSC markers in this study could potentially increase the therapeutic efficacy of TMSCs in clinical applications.

The renoprotective effects of soy protein in the aging rat kidney

Aging is a risk factor for chronic kidney disease (CKD) and is itself associated with alterations in renal structure and function. There are no specific interventions to attenuate age-dependent renal dysfunction and the mechanism(s) responsible for these deficits have not been fully elucidated. In this study, male Fischer 344 rats, which develop age-dependent nephropathy, were feed a casein- or soy protein diet beginning at 16 mon (late life intervention) and renal structure and function was assessed at 20 mon. The soy diet did not significantly affect body weight, but was renoprotective as assessed by decreased proteinuria, increased glomerular filtration rate (GFR) and decreased urinary kidney injury molecule-1 (Kim-1). Renal fibrosis, as assessed by hydroxyproline content, was decreased by the soy diet, as were several indicators of inflammation. RNA sequencing identified several candidates for the renoprotective effects of soy, including decreased expression of Twist2, a basic helix-loop-helix transcription factor that network analysis suggest may regulate the expression of several genes associated with renal dysfunction. Twist2 expression is upregulated in the aging kidney and the unilateral ureteral obstruction of fibrosis; the expression is limited to distal tubules of mice. Taken together, these data demonstrate the renoprotective potential of soy protein, putatively by reducing inflammation and fibrosis, and identify Twist2 as a novel mediator of renal dysfunction that is targeted by soy.

Fabrication, characterization and biocompatibility of collagen/oxidized regenerated cellulose-Ca composite scaffold for carrying Schwann cells

Schwann cell (SC) is the primary structural and functional part of the peripheral nervous system, and it plays a key role in the repair and regeneration of peripheral nerve. In order to develop a suitable scaffold for SC nerve tissue engineering, three kinds of scaffolds, including pristine collagen, pure oxidized regenerated cellulose-Ca (ORCCa) and collagen/ORC-Ca composite scaffolds, have been fabricated for carrying SC in this study. SC is then seeded on the scaffolds to form SC-scaffold nerve tissue engineering composites and evaluate their biocompatibility. The chemical and physical structure of the scaffolds are investigated by FTIR, NMR and SEM. The wettability of the collagen/ORC-Ca composite scaffold is close to that of pristine collagen, and the tensile strength of the composite scaffold (0.58 MPa) is better than that of pristine collagen (0.36 MPa). Cytotoxicity, cell proliferation, cell adhesion and western blotting assays are conducted to evaluate the biocompatibility and properties of different scaffolds. The results show that the three scaffolds exhibit no toxicity, and the proliferation rate of SC on the collagen/ORC-Ca composite scaffold is significantly higher than that of the other scaffolds (p < 0.05). The number of the adhesion cells on the composite scaffold (244.67 ± 13.02) is much more than that in the pure ORC-Ca group (p < 0.01). Furthermore, the expression of N-Cadheri and PMP22 proteins in the collagen/ORC-Ca composite scaffold is significantly superior to the other two scaffolds (both p < 0.01). Therefore, it could be concluded that the collagen/ORC-Ca composite is a promising candidate as a scaffold for carrying SC to form nerve tissue engineering composites in order to assist the peripheral nervous in the repair and regeneration.

Rejuvenating Strategies for Stem Cell-Based Therapies in Aging

Recent advances in our understanding of tissue regeneration and the development of efficient approaches to induce and differentiate pluripotent stem cells for cell replacement therapies promise exciting avenues for treating degenerative age-related diseases. However, clinical studies and insights from model organisms have identified major roadblocks that normal aging processes impose on tissue regeneration. These new insights suggest that specific targeting of environmental niche components, including growth factors, ECM, and immune cells, and intrinsic stem cell properties that are affected by aging will be critical for the development of new strategies to improve stem cell function and optimize tissue repair processes.

The impact of aging on epithelial barriers

The epithelium has many critical roles in homeostasis, including an essential responsibility in establishing tissue barriers. In addition to the fundamental role in separating internal from external environment, epithelial barriers maintain nutrient, fluid, electrolyte and metabolic waste balance in multiple organs. While, by definition, barrier function is conserved, the structure of the epithelium varies across organs. For example, the skin barrier is a squamous layer of cells with distinct structural features, while the lung barrier is composed of a very thin single cell to minimize diffusion space. With the increased focus on age-dependent alterations in organ structure and function, there is an emerging interest in the impact of age on epithelial barriers. This review will focus on the impact of aging on the epithelial barrier of several organs, including the skin, lung, gastrointestinal tract and the kidney, at a structural and functional level.

AGE-RELATED CLINICAL OUTCOME AFTER MACULAR HOLE SURGERY

PURPOSE

To evaluate functional and anatomical retinal recovery according to patient age using spectral domain optical coherence tomography in eyes with surgically closed macular holes.

METHODS

We retrospectively studied 83 eyes with anatomically closed idiopathic macular holes after surgery confirmed by spectral domain optical coherence tomography. Patients were divided into four subgroups based on age (Group 1: ≤ 60, Group 2: 61-65, Group 3: 66-70, Group 4: > 70). Best-corrected visual acuity and reconstruction of the external limiting membrane and ellipsoid zone after surgery were documented for 12 months.

RESULTS

Mean patient age was 64.5 ± 9.8 years (range 44-81). Mean visual improvement in logMAR units (ETDRS letter score) at 12 months was worse in older age subgroups (Group 1: 0.4 ± 0.3 [20], Group 2: 0.4 ± 0.3 [20], Group 3: 0.2 ± 0.3 [10], Group 4: 0.1 ± 0.3 [5], P = 0.001). When age was more than 65 years, total number of eyes with restored retinal microstructure after surgery was lower (22 eyes, 53.7%; 32 eyes, 76.2%; P = 0.018) and time (months) to structural recovery was longer (10.2, 7.1, P < 0.001) than age under 65 years. Visual improvement corresponded to recovery of the outer retinal layers. In multivariate analysis, patients of older age (odds ratio, 0.91; 95% CI, 0.89-0.93) had less visual improvement at month 12.

CONCLUSION

Poor visual outcomes and delayed microstructural recovery occurred in older subjects after anatomically closed macular hole surgery. Older age may be indicative of poor clinical outcome in repaired macular holes.

Aging asymmetry: systematic survey of changes in age-related biomarkers in the annual fish Nothobranchius guentheri

Aging asymmetry is the observation that different tissues age in different ways and at different rates. This has not been assessed in a single organism using multiple biomarkers of aging. Here we clearly demonstrated that the levels of protein oxidation and lipid peroxidation as well as CAT, SOD and GPX activities all showed a tissue-dependent change with advancing age; and DNA repair ability, as revealed by the expression of ercc1 and its protein levels, also exhibited a tissue-specific variation with age. We also found that protein oxidation and lipid peroxidation levels remained relatively stable in the liver, intestine, skin and testis as well as in the brain, eye and heart of young, adult and aged fishes; SOD and GPX activities displayed little variation in the intestine, eye and skin as well as in the brain and skin of young, adult and aged fishes; and low and stable expression of ercc1 was observed in the spleen, eye and heart of young, adult and aged fishes. Collectively, these results indicate that aging is tissue specific and asymmetric in N. guentheri. The observation of aging asymmetry may have practical implications for the application of non-intrusion intervention approaches to prolong lifespan.

The Emerging Role of DNA Methylation in Kidney Transplantation: A Perspective

Allograft outcome depends on a range of factors, including donor age, the allo-immune response, ischemia-reperfusion injury, and interstitial fibrosis of the allograft. Changes in the epigenome, and in DNA methylation in particular, have been implicated in each of these processes, in either the kidney or other organ systems. This review provides a primer for DNA methylation analyses and a discussion of the strengths and weaknesses of current studies, but it is also a perspective for future DNA methylation research in kidney transplantation. We present exciting prospects for leveraging DNA methylation analyses as a tool in kidney biology research, and as a diagnostic or prognostic marker for predicting allograft quality and success. Topics discussed include DNA methylation changes in aging and in response to hypoxia and oxidative stress upon ischemia-reperfusion injury. Moreover, emerging evidence suggests that DNA methylation contributes to organ fibrosis and that systemic DNA methylation alterations correlate with the rate of kidney function decline in patients with chronic kidney disease and end-stage renal failure. Monitoring or targeting the epigenome could therefore reveal novel therapeutic approaches in transplantation and open up paths to biomarker discovery and targeted therapy.

Dynamic changes of global DNA methylation and hypermethylation of cell adhesion-related genes in rat kidneys in response to ochratoxin A

Ochratoxin A (OTA), which is found in a variety of food products, is associated with the development of nephrotoxicity and carcinogenicity in rats and has raised public health concerns. A previous study in our laboratory indicated that OTA exposure induced cytotoxicity by decreasing global DNA methylation in vitro. However, the relationship between OTA-induced nephrotoxicity and DNA methylation changes in vivo remains unclear. The object of this study was to investigate whether OTA can change global DNA methylation or alter the expression of several critical tumour-related genes by inducing methylation modifications before carcinogenesis. We focused on the mechanism of action of OTA in regard to DNA methylation, including the expression of DNA methyltransferases and the regulation of specific cell signalling pathways. Dynamic and dose-dependent changes of global DNA methylation were observed during OTA-induced nephrotoxicity and probably associated with the expression of DNA methyltransferase 1. 13-week exposure of OTA caused hypermethylation in the promoters of critical cell adhesion-related genes, E-cadherin and N-cadherin, leading to reduction of the corresponding mRNA expression, accompanied by transcriptional activation of the Wnt and PI3K/AKT pathways. These findings suggested that long-term OTA exposure could disrupt DNA methylation profile, which might be one of the possible mechanisms of OTA-induced nephrotoxicity.

A role for the age-dependent loss of α(E)-catenin in regulation of N-cadherin expression and cell migration

The aging kidney has a decreased ability to repair following acute kidney injury. Previous studies from our laboratory have demonstrated a loss in α‐catenin expression in the aging rat kidney. We hypothesize that loss of α‐catenin expression in tubular epithelial cells may induce changes that result in a decreased repair capacity. In these studies, we demonstrate that decreased α‐catenin protein expression is detectable as early as 20 months of age in male Fischer 344 rats. Protein loss is also observed in aged nonhuman primate kidneys, suggesting that this is not a species‐specific response. In an effort to elucidate alterations due to the loss of α‐catenin, we generated NRK‐52E cell lines with stable knockdown of α(E)‐catenin (C2 cells). Interestingly, C2 cells had decreased expression of N‐cadherin, decreased cell–cell adhesion, and increased monolayer permeability. C2 had deficits in wound repair, due to alterations in cell migration. Analysis of gene expression in the migrating control cells indicated that expression of N‐cadherin and N‐CAM was increased during repair. In migrating C2 cells, expression of N‐CAM was also increased, but the expression of N‐cadherin was not upregulated. Importantly, a blocking antibody against N‐cadherin inhibited repair in NRK‐52E cells, suggesting an important role in repair. Taken together, these data suggest that loss of α‐catenin, and the subsequent downregulation of N‐cadherin expression, is a mechanism underlying the decreased migration of tubular epithelial cells that contributes to the inability of the aging kidney to repair following injury.

Aging is associated with loss of α‐catenin and N‐cadherin expression in the kidney. In these studies, we demonstrate that α‐catenin regulates, in part, N‐cadherin expression and migration in tubular epithelial cells.

SH2B1β interacts with STAT3 and enhances fibroblast growth factor 1-induced gene expression during neuronal differentiation

Neurite outgrowth is an essential process during neuronal differentiation as well as neuroregeneration. Thus, understanding the molecular and cellular control of neurite outgrowth will benefit patients with neurological diseases. We have previously shown that overexpression of the signaling adaptor protein SH2B1β promotes fibroblast growth factor 1 (FGF1)-induced neurite outgrowth (W. F. Lin, C. J. Chen, Y. J. Chang, S. L. Chen, I. M. Chiu, and L. Chen, Cell. Signal. 21:1060-1072, 2009). SH2B1β also undergoes nucleocytoplasmic shuttling and regulates a subset of neurotrophin-induced genes. Although these findings suggest that SH2B1β regulates gene expression, the nuclear role of SH2B1β was not known. In this study, we show that SH2B1β interacts with the transcription factor, signal transducer, and activator of transcription 3 (STAT3) in neuronal PC12 cells, cortical neurons, and COS7 fibroblasts. By affecting the subcellular distribution of STAT3, SH2B1β increased serine phosphorylation and the concomitant transcriptional activity of STAT3. As a result, overexpressing SH2B1β enhanced FGF1-induced expression of STAT3 target genes Egr1 and Cdh2. Chromatin immunoprecipitation assays further reveal that, in response to FGF1, overexpression of SH2B1β promotes the in vivo occupancy of STAT3-Sp1 heterodimers at the promoter of Egr1 and Cdh2. These findings establish a central role of SH2B1β in orchestrating signaling events to transcriptional activation through interacting and regulating STAT3-containing complexes during neuronal differentiation.

Overexpression of MMP-7 Increases Collagen 1A2 in the Aging Kidney

The percentage of the U.S. population over 65 is rapidly increasing, as is the incidence of chronic kidney disease (CKD). The kidney is susceptible to age-dependent alterations in structure, specifically tubulointerstitial fibrosis that leads to CKD. Matrix metalloproteinases (MMPs) were initially characterized as extracellular matrix (ECM) proteinases; however, it is clear that their biological role is much larger. We have observed increased gene expression of several MMPs in the aging kidney, including MMP-7. MMP-7 overexpression was observed starting at 16 months, with over a 500-fold upregulation in 2-year-old animals. Overexpression of MMP-7 is not observed in age-matched, calorically restricted controls that do not develop fibrosis and renal dysfunction, suggesting a role in the pathogenesis. In order to delineate the contributions of MMP-7 to renal dysfunction, we overexpressed MMP-7 in NRK-52E cells. High-throughput sequencing of the cells revealed that two collagen genes, Col1a2 and Col3a1, were elevated in the MMP-7 overexpressing cells. These two collagen genes were also elevated in aging rat kidneys and temporally correlated with increased MMP-7 expression. Addition of exogenous MMP-7, or conditioned media from MMP-7 overexpressing cells also increased Col1A2 expression. Inhibition of protein kinase A (PKA), src, and MAPK signaling at p38 and ERK was able to attenuate the MMP-7 upregulation of Col1a2. Consistent with this finding, increased phosphorylation of PKA, src, and ERK was seen in MMP-7 overexpressing cells and upon exogenous MMP-7 treatment of NRK-52E cells. These data suggest a novel mechanism by which MMP-7 contributes to the development of fibrosis leading to CKD.

Structural equation modeling highlights the potential of Kim-1 as a biomarker for chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is a major public health problem, and despite continued research in the field, there is still a need to identify both biomarkers of risk and progression, as well as potential therapeutic targets. Structural equation modeling (SEM) is a family of statistical techniques that has been utilized in the fields of sociology and psychology for many years; however, its utilization in the biological sciences is relatively novel. SEM's ability to investigate complex relationships in an efficient, single model could be utilized to understand the progression of CKD, as well as to develop a predictive model to assess kidney status in the patient.

METHODS

Fischer 344 rats were fed either an ad libitum diet or a calorically restricted diet, and a time-course study of kidney structure and function was performed. EQS, a SEM software package, was utilized to generate five CKD models of the Fisher 344 rat and identify relationships between measured variables and estimates of kidney damage and kidney function.

RESULTS

All models identified strong relationships between a biomarker for CKD, kidney injury molecule-1 (Kim-1) and kidney damage, in the Fischer 344 rat CKD model. Models also indicate a strong relationship between age and renal damage and dysfunction.

CONCLUSION

SEM can be used to model CKD and could be useful to examine biomarkers in CKD patients.

Aberrant methylation accounts for cell adhesion-related gene silencing during 3-methylcholanthrene and diethylnitrosamine induced multistep rat lung carcinogenesis associated with overexpression of DNA methyltransferases 1 and 3a

To evaluate the significance of alterations in cell adhesion-related genes methylation during lung multistep carcinogenesis induced by the genotoxic carcinogens 3-methylcholanthrene (MCA) and diethylnitrosamine (DEN), tissue samples microdissected from MCA/DEN-induced rat lung carcinogenesis model were subjected to methylation-specific PCR to evaluate the DNA methylation status of CADM1, TIMP3, E-cadherin and N-cadherin. Immunohistochemistry was used to determine protein expression of CADM1, TIMP3, N-cadherin and the DNA methyltransferases (DNMTs) 1, 3a and 3b. E-cadherin hypermethylation was not detected in any tissue. CADM1, TIMP3 and N-cadherin hypermethylation was correlated with the loss of their protein expression during the progression of pathologic lesions. The prevalence of DNA methylation of at least one gene and the average number of methylated genes increased with the histological progression. DNMT1 and DNMT3a protein expression increased progressively during the stages of lung carcinogenesis, whereas DNMT3b overexpression was only found in several samples. Furthermore, DNMT1 protein expression levels were correlated with CADM1 methylation, and DNMT3a protein expression levels were correlated with CADM1, TIMP3 and N-cadherin methylation. The average number of methylated genes during carcinogenesis was significantly correlated with DNMT1 and DNMT3a protein expression levels. Moreover, mRNA expression of CADM1 significantly increased after treatment with DNMT inhibitor 5-aza-2'-deoxycytidine in CADM1-methylated primary tumor cell lines. Our findings suggest that an accumulation of hypermethylation accounts for cell adhesion-related gene silencing is associated with dynamic changes in the progression of MCA/DEN-induced rat lung carcinogenesis. We suggest that DNMT1 and DNMT3a protein overexpression may be responsible for this aberrant DNA methylation.

Tissue-specific dysregulation of DNA methylation in aging

The normal aging process is a complex phenomenon associated with physiological alterations in the function of cells and organs over time. Although an attractive candidate for mediating transcriptional dysregulation, the contribution of epigenetic dysregulation to these progressive changes in cellular physiology remains unclear. In this study, we employed the genome-wide HpaII tiny fragment enrichment by ligation-mediated PCR assay to define patterns of cytosine methylation throughout the rat genome and the luminometric methylation analysis assay to measure global levels of DNA methylation in the same samples. We studied both liver and visceral adipose tissues and demonstrated significant differences in DNA methylation with age at > 5% of sites analyzed. Furthermore, we showed that epigenetic dysregulation with age is a highly tissue-dependent phenomenon. The most distinctive loci were located at intergenic sequences and conserved noncoding elements, and not at promoters nor at CG-dinucleotide-dense loci. Despite this, we found that there was a subset of genes at which cytosine methylation and gene expression changes were concordant. Finally, we demonstrated that changes in methylation occur consistently near genes that are involved in metabolism and metabolic regulation, implicating their potential role in the pathogenesis of age-related diseases. We conclude that different patterns of epigenetic dysregulation occur in each tissue over time and may cause some of the physiological changes associated with normal aging.

Experimental approaches to the study of epigenomic dysregulation in ageing

In this review, we describe how normal ageing may involve the acquisition of epigenetic errors over time, akin to the accumulation of genetic mutations with ageing. We describe how such experiments are currently performed, their limitations technically and analytically and their application to ageing research.

DNA methylation, an epigenetic mechanism connecting folate to healthy embryonic development and aging

Experimental studies demonstrated that maternal exposure to certain environmental and dietary factors during early embryonic development can influence the phenotype of offspring as well as the risk of disease development at the later life. DNA methylation, an epigenetic phenomenon, has been suggested as a mechanism by which maternal nutrients affect the phenotype of their offspring in both honeybee and agouti mouse models. Phenotypic changes through DNA methylation can be linked to folate metabolism by the knowledge that folate, a coenzyme of one-carbon metabolism, is directly involved in methyl group transfer for DNA methylation. During the fetal period, organ-specific DNA methylation patterns are established through epigenetic reprogramming. However, established DNA methylation patterns are not immutable and can be modified during our lifetime by the environment. Aberrant changes in DNA methylation with diet may lead to the development of age-associated diseases including cancer. It is also known that the aging process by itself is accompanied by alterations in DNA methylation. Diminished activity of DNA methyltransferases (Dnmts) can be a potential mechanism for the decreased genomic DNA methylation during aging, along with reduced folate intake and altered folate metabolism. Progressive hypermethylation in promoter regions of certain genes is observed throughout aging, and repression of tumor suppressors induced by this epigenetic mechanism appears to be associated with cancer development. In this review, we address the effect of folate on early development and aging through an epigenetic mechanism, DNA methylation.

Ageing mouse kidney--not always the SAME old story

BACKGROUND

As interest in the ageing kidney grows rapidly, more experimental ageing studies are conducted in the field. One of the main obstacles that researchers have to face is that studies in old animals are often less reproducible than in young animals. We have observed that the aged animal's provenance can be an overlooked factor accounting for such experimental heterogeneity.

METHODS

Male C57BL/6J mice aged 19-22 months were purchased from four different suppliers. Baseline renal parameters were evaluated by measuring serum urea, serum creatinine and proteinuria. Renal morphology was analysed by quantifying glomerulosclerosis, interstitial fibrosis and amyloid deposits on paraffin sections stained with PAS, Masson trichrome, Sirius red and Congo red.

RESULTS

We found normal renal ageing in mice from three sources, but an unexpected renal pathology in mice from one major European supplier. Mice from this supplier had significantly elevated serum urea, creatinine values and an increased urinary protein excretion. Corresponding kidneys displayed massive glomerulosclerosis with evidence of amyloid deposits and increased interstitial fibrosis.

CONCLUSIONS

Supplier-dependent differences, such as observed here, can explain irreproducibility of experimental results in renal ageing research. This can be avoided by careful baseline analysis prior to in vivo experiments.

Sex differences in the developmental origins of hypertension and cardiorenal disease

The "developmental origins of health and disease" (DOHAD) hypothesis derives from clinical observations, indicating long-term health consequences for persons of low birth weight. There is growing evidence, primarily from animal studies, that supports the idea that processes put in motion during development that contribute to DOHAD do not necessarily reflect as significantly compromised growth and altered birth weight. Throughout the body of work investigating the DOHAD hypothesis, several themes have emerged; the importance of the placenta, the presence of critical periods of vulnerability, the involvement of the kidney in programmed hypertension, the presence of sex differences in the progression and development of adult diseases. Despite compelling findings in recent studies, much remains unclear regarding the impact of biological sex in the progression of human diseases, in general, and in the mechanisms underlying developmentally programmed responses, in particular. Although the contribution of biological sex to DOHAD is increasingly recognized, it also appears that it may exert distinctly different influences during fetal and adult life. The mechanisms by which biological sex contributes to these processes remains nebulous at present; nevertheless, several intriguing mechanistic candidates have been proposed ranging from differences in the amounts of sex hormones (e.g., estrogens, androgens) to recently described sexual dimorphism in the transcriptome of a variety of mammalian tissues. Recognizing the influences of biological sex or sex hormones on DOHAD uniquely situates research in this area to provide significant insights into the development and progression of many diseases, recent examples of which are the subject of this review.

Kidney-specific expression of human organic cation transporter 2 (OCT2/SLC22A2) is regulated by DNA methylation

Human organic cation transporter 2 (OCT2/SLC22A2), which is specifically expressed in the kidney, plays critical roles in the renal secretion of cationic compounds. Tissue expression and membrane localization of OCT2 are closely related to the tissue distribution, pharmacological effects, and/or adverse effects of its substrate drugs. However, the molecular mechanisms underlying the kidney-specific expression of OCT2 have not been elucidated. In the present study, therefore, we examined the contribution of DNA methylation of the promoter region for the OCT2 gene to its tissue-specific expression using human tissue samples. In vivo methylation status of the proximal promoter region of OCT2 and that of OCT1, a liver-specific organic cation transporter, were investigated by bisulfite sequencing using human genomic DNA extracted from the kidney and liver. All CpG sites in the OCT2 proximal promoter were hypermethylated in the liver, while hypomethylated in the kidney. On the other hand, the promoter region of OCT1 was hypermethylated in both the kidney and liver. The level of methylation of the OCT2 promoter was especially low at the CpG site in the E-box, the binding site of the basal transcription factor upstream stimulating factor (USF) 1. In vitro methylation of the OCT2 proximal promoter dramatically reduced the transcriptional activity, and an electrophoretic mobility shift assay showed that methylation at the E-box inhibited the binding of USF1. These results indicate that kidney-specific expression of human OCT2 is regulated by methylation of the proximal promoter region, interfering with the transactivation by USF1.

Msh2 promoter region hypermethylation as a marker of aging-related deterioration in old retired female breeder mice

Aging is a process where individuals decrease the performance of their physiological systems and cellular stress response, making them more susceptible to disease and death. The increase in DNA damage associated with age might be recognized as the accumulation of physiological and environmentally induced mutations accompanied with a decline in DNA repair. DNA mismatch repair (MMR) is the main postreplicative correction pathway, which is known to decrease with age. However, since infrequent occurrence of direct DNA damage contrasts with the extensive cell and tissue dysfunction seen in older individuals, the withdrawing of DNA-repairing systems might be also related to epigenetic changes, such as DNA methylation. It has been reported that the physiological stress related to breeding might accelerate the acquisition of aging-related markers; therefore, the aim of this work was to link age with epigenetic modifications in this animal population. Hence, the correlation of Msh2 gene silencing with the deterioration of breeding female mice associated to aging was determined. Combined bisulfite restriction analysis assay was used to compare methylation on DNA isolated from twelve-month-old retired breeders against nulliparous female mice aged-matched, and two-month-old young adults. Our experiments clearly reveal Msh2 promoter hypermethylation associated to the aging process. A higher degree methylation was additionally observed in breeding females DNA. Nevertheless, this additional methylation did not correlate with a further decrease Msh2 mRNA, suggesting that the increase in methylation in old retired breeder might account for further epigenetic changes that could additionally promote the aging process.