Strikingly, miR-29a serum levels Everolimus molecular weight were significantly down-regulated in patients with liver fibrosis/cirrhosis compared with healthy controls, and low serum miR-29a levels were associated with advanced cirrhosis stages. The molecular process that leads to lower serum levels of miR-29a in patients with cirrhosis is not clear. It was previously demonstrated that miRNAs are packed into exosomes, which can be exchanged between cells without loss of function of the included miRNA.23 This raises the
question whether miRNAs may play a role as extracellular messengers mediating intercellular communication. Despite the currently unknown mechanism of miRNA regulation in the serum, the striking regulation of miR-29a in the serum of cirrhosis patients might have implications for clinical aspects of liver cirrhosis. Therefore, larger patient cohorts with distinct hepatic disease-causes selleck compound and differential fibrosis states will have to be analyzed to further test the potential of miR-29 levels in the serum as biomarkers for detection or monitoring of liver fibrosis. Because serum-miR29a levels were significantly different but still showed some overlap between fibrosis and control patients, it is likely that not one miRNA but detection of a whole panel might provide the necessary sensitivity and specificity for diagnosis and monitoring of chronic liver
diseases. In the current study, we provide evidence for the hypothesis that different upstream signals regulate the expression levels of miR-29 during liver fibrosis in vivo and in HSCs in vitro (Fig. 7A). Although TGF-β–dependent down-regulation of miR-29 correlated with increased collagen expression, this was not the case for LPS-dependent miR regulation. The reason for this discrepancy is currently
unknown. In line with our findings, it was previously shown that LPS Phosphoprotein phosphatase stimulation alone does not lead to increased collagen production in HSCs.24 It is possible that miR-29–dependent effects on their target mRNAs require a previous strong induction of the respective extracellular matrix genes by TGF-β. Conversely, interleukin-1, which normally also activates NF-κB, did not have a similar effect on miR-29 as LPS or TNF. Thus, it is possible that the regulatory network downstream of inflammatory signals is more complex than the more linear TGF-β/miR-29/collagen cascade. Stress-related signaling cascades other than NF-κB might influence miR-29 expression downstream of inflammatory receptors such as toll-like receptors or TNF. In line with this hypothesis, it was recently demonstrated that oxidative stress leads to a down-regulation of miR-29 in human trabecular meshwork cells.25 Conversely, these various signals might “neutralize” the effects of miR-29 on collagen mRNA levels on LPS stimulation.