Date Published: May 29, 2018
Publisher: Impact Journals
Author(s): Oleg Denisenko, Daniel Mar, Matthew Trawczynski, Karol Bomsztyk.
Dysregulation of gene expression is a hallmark of aging. We examined epigenetic mechanisms that mediate aberrant expression of laminin genes in aging rat kidneys. In old animals, no alterations were found in the levels of abundant laminin mRNAs, whereas Lama3, b3, and c2 transcripts were increased compared to young animals. Lamc2 showed the strongest changes at the mRNA and protein levels. Lamc2 upregulation was transcriptional, as indicated by the elevated RNA polymerase II density at the gene. Furthermore, aging is associated with the loss of H3K27m3 and 5mC silencing modifications at the Lamc2 gene. Western blot analysis revealed no changes in cellular levels of H3K27m3 and cognate enzyme Ezh2 in old kidneys. Thus, the decrease in H3K27m3 at Lamc2 resulted from the re-distribution of this mark among genomic sites. Studies in kidney cells in vitro showed that reducing H3K27m3 density with Ezh2 inhibitor had no effect on Lamc2 expression, suggesting that this modification plays little role in gene upregulation in aging kidney. In contrast, treatment with DNA methylation inhibitor 2′-deoxy-5-azacytidine was sufficient to upregulate Lamc2 gene. We suggest that the loss of 5mC at silenced laminin genes drives their de-repression during aging, contributing to the age-related decline in renal function.
In organisms as diverse as yeast and humans, age-related changes in chromatin structure contribute to alterations in gene expression and progression to aging phenotypes . The extracellular matrix (ECM) defines tissue compartments and orchestrates organ development and function . ECM structure and function are altered with aging [3,4]. Specifically, one of the hallmarks of aging kidneys is the aberrant accumulation of ECM proteins in the interstitium (interstitial fibrosis) [5,6]. These alterations contribute to the age-related decline of kidney function, culminating in the organism’s death. Previously we have shown that, during aging, transcription of the ECM gene Col3a1 is increased in rat kidneys, a finding associated with aberrant accumulation of collagen III protein in the interstitium .
We found that expression of ECM laminin genes was dysregulated during aging. In F344 and FBN-F1 rat kidneys, transcription of three genes that are expressed at very low levels in young animals – Lama3, Lamb3, and Lamc2 – progressively increased with age. These genes encode subunits of laminin 5 hetero-trimer (Ln5, laminin 332, kalinin), a major component of epidermal basement membranes and a marker of the wound healing process [33–35]. Increased expression of these genes may contribute to the development of glomerulosclerosis and tubulointerstitial fibrosis in old kidneys [6,7]. We present evidence that the loss of epigenetic gene silencing is responsible, at least in part, for the upregulation of these genes in aging kidneys.