Comparative profiles of DNA methylation and differential gene expression in osteocytic areas from aged and young mice

Altered DNA methylation upon ageing may result in many age-related diseases such as osteoporosis. However, the changes in DNA methylation that occur in cortical bones, the major osteocytic areas, remain unknown. In our study, we extracted total DNA and RNA from the cortical bones of 6-month-old and 24-month-old mice and systematically analysed the differentially methylated regions (DMRs), differentially methylated promoters (DMPs) and differentially expressed genes (DEGs) between the mouse groups. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of the DMR-related genes revealed that they were mainly associated with metabolic signalling pathways, including glycolysis, fatty acid and amino acid metabolism. Other genes with DMRs were related to signalling pathways that regulate the growth and development of cells, including the PI3K-AKT, Ras and Rap1 signalling pathways. The gene expression profiles indicated that the DEGs were mainly involved in metabolic pathways and the PI3K-AKT signalling pathway, and the profiles were verified through real-time quantitative PCR (RT-qPCR). Due to the pivotal roles of the affected genes in maintaining bone homeostasis, we suspect that these changes may be key factors in age-related bone loss, either together or individually. Our study may provide a novel perspective for understanding the osteocyte and its relationship with osteoporosis during ageing. SIGNIFICANCE OF THE STUDY: Our study identified age-related changes in gene expressions in osteocytic areas through whole-genome bisulfite sequencing (WGBS) and RNA-seq, providing new theoretical foundations for the targeted treatment of senile osteoporosis.

The systemic nature of CKD

The accurate definition and staging of chronic kidney disease (CKD) is one of the major achievements of modern nephrology. Intensive research is now being undertaken to unravel the risk factors and pathophysiologic underpinnings of this disease. In particular, the relationships between the kidney and other organs have been comprehensively investigated in experimental and clinical studies in the last two decades. Owing to technological and analytical limitations, these links have been studied with a reductionist approach focusing on two organs at a time, such as the heart and the kidney or the bone and the kidney. Here, we discuss studies that highlight the complex and systemic nature of CKD. Energy balance, innate immunity and neuroendocrine signalling are highly integrated biological phenomena. The diseased kidney disrupts such integration and generates a high-risk phenotype with a clinical profile encompassing inflammation, protein-energy wasting, altered function of the autonomic and central nervous systems and cardiopulmonary, vascular and bone diseases. A systems biology approach to CKD using omics techniques will hopefully enable in-depth study of the pathophysiology of this systemic disease, and has the potential to unravel critical pathways that can be targeted for CKD prevention and therapy.

Gene expression profile in bone of diabetes-prone BB/OK rats fed a high-fat diet

A high-fat diet (HFD) has been recognized as a risk factor for diseases such as dyslipidemia, atherosclerosis, obesity, and osteoporosis. However, studies analyzing gene expression after HFD in bone are rare. That prompted us to analyze the expression of selected genes in bone of 4-week-old diabetes-prone B(io)B(reeding) rats. Two breeding pairs were fed a HFD (+10 % tallow) or were fed a normal diet (ND; Ssniff R-Z) before mating and afterward during pregnancy. After the birth of progeny, parents continued to be given HFD or ND until the progeny was weaned (3 weeks). Thereafter, offspring were weaned and were fed the same food as their parents up to an age of 4 weeks. Body weight was measured at an age of 4 weeks, and subsequently 13 HFD rats and 13 ND rats were killed and the tibial bone was harvested to analyze the expression of 53 genes in bone. All rats fed HFD were significantly heavier than rats fed ND after 3 and 4 weeks. The diet also influenced the expression of genes in bone. There were significant differences in 20 out of 53 genes studied between rats fed HFD compared with rats fed ND. Four out of 20 had a lower and 17 out of 20 genes a higher expression in HFD rats, but differences in gene expression showed obvious differences between males and females. There were only two genes that were similarly different between males and females: Bmp4 and Atf4. Two genes, Foxg1 and Npy, were inversely expressed in males and females. It seems that the gene expression is differently regulated by diet during pregnancy and later in life between males and females. Nevertheless, it cannot be excluded that HFD also acts as an epigenetic factor in the development of offspring in utero.

Evolution of leptin structure and function

Leptin, the protein product of the obese(ob or Lep) gene, is a hormone synthesized by adipocytes that signals available energy reserves to the brain, and thereby influences development, growth, metabolism and reproduction. In mammals, leptin functions as an adiposity signal: circulating leptin fluctuates in proportion to fat mass, and it acts on the hypothalamus to suppress food intake. Orthologs of mammalian Lep genes were recently isolated from several fish and two amphibian species, and here we report the identification of two Lep genes in a reptile, the lizard Anolis carolinensis. While vertebrate leptins show large divergence in their primary amino acid sequence, they form similar tertiary structures, and may have similar potencies when tested in vitro on heterologous leptin receptors (LepRs). Leptin binds to LepRs on the plasma membrane, activating several intracellular signaling pathways. Vertebrate LepRs signal via the Janus kinase (Jak) and signal transducer and activator of transcription (STAT) pathway. Three tyrosine residues located within the LepR cytoplasmic domain are phosphorylated by Jak2 and are required for activation of SH2-containing tyrosine phosphatase-2, STAT5 and STAT3 signaling. These tyrosines are conserved from fishes to mammals, demonstrating their critical role in signaling by the LepR. Leptin is anorexigenic in representatives of all vertebrate classes, suggesting that its role in energy balance is ancient and has been evolutionarily conserved. In addition to its integral role as a regulator of appetite and energy balance, leptin exerts pleiotropic actions in development, physiology and behavior.