Tiny RNA Molecule Found to Regulate Collagen, Fibrosis in SSc-ILD

A tiny RNA molecule called microRNA-320a is associated with regulating collagen levels and fibrosis, or scarring, in systemic sclerosis (SSc) complicated by interstitial lung disease (ILD), a study reports. 

According to investigators, this is the “first evidence” of a link between levels of microRNA-320a and scarring in patients with SSc-ILD.

Learning more about the underlying mechanisms may provide new therapeutic strategies for treating scleroderma with ILD, they said.

The study, “MicroRNA-320a: an important regulator in the fibrotic process in interstitial lung disease of systemic sclerosis,” was published in the journal Arthritis Research & Therapy.

SSc, or scleroderma, is characterized by the activation of collagen-producing fibroblast cells and a toxic buildup of collagen. That buildup results in progressive tissue scarring (fibrosis) and ultimately organ failure. Around two-thirds of SSc cases are complicated by interstitial lung disease — fibrosis of the lungs — which is the leading cause of SSc-related death.

While RNA typically contains information to produce proteins, microRNAs are short RNAs that regulate gene activity. Although the exact mechanisms are not well understood, several microRNAs —  known as miRNAs — are thought to be involved in the regulation of collagens. These miRNAs also are believed to play a role in signaling pathways related to fibrosis, such as transforming growth factor (TGF)-beta. 

Now, seeking to learn more, researchers in China investigated the role of miRNAs in SSc-ILD. They used blood samples and peripheral blood mononuclear cells — which include immune T-cells and monocytes — from SSc-ILD patients and a mouse model of the disorder.

Blood samples were collected from five female SSc patients, three with and two without ILD, and three healthy people (controls). The analysis revealed a decrease in 18 miRNAs in SSc patients and an increase in seven. Compared with those without ILD, the SSc-ILD patients had 18 decreased and five increased miRNAs, along with an increase in expression (activity) of genes associated with cell growth, cell death, and production of the fibrosis-related protein fibronectin.

From the 18 miRNAs that were reduced in SSc-ILD patients, the investigators selected five that had been linked previously to lung fibrosis to analyze further. These five miRNAs were evaluated in 17 patients with and 13 without ILD, as well as 16 healthy individuals (controls).

Notably, three of the five selected miRNAs belonged to the microRNA 320 family. One, microRNA-320a, showed the most pronounced decrease in both SSc compared with controls and SSc-ILD compared with SSc without ILD.

MicroRNA-320a levels were significantly decreased in the lung tissue of mice with SSc-like symptoms, while 1,144 genes were increased. Most associated with inflammation, immune response, and fibrosis.

Overexpression of microRNA-320a in healthy human lung fibroblasts dramatically reduced the expression of type I and III collagen, while a reduction of microRNA-320a significantly increased these genes’ activity. The results suggest that microRNA-320a regulates collagen gene expression. 

Three genes involved in fibrosis — TGFBR1, TGFBR2, and IGF1R — are potential targets of microRNA-320a, with the first two involved in the TGF-beta pathway. To assess this, the research team developed a reporter gene system that shows decreased activity when a miRNA binds to a target gene sequence. 

Increased expression of microRNA-320a overexpression in healthy lung fibroblasts decreased the gene and protein levels of both targets, indicating that microRNA-320a is specifically binding to and regulating TGFBR2 and IGF1R.

When healthy lung fibroblasts were stimulated by TGF-beta, expression of microRNA-320a and both COL1A1, and COL3A1 — which code for collagen type I and III — significantly increased. Those findings suggest that microRNA-320a production in fibroblasts is induced by TGF-beta and may play a role in fibrosis through the regulation of collagen.

“This is the first evidence supporting the association of [microRNA-320a] levels with SSc-ILD patients and the identification of a fibrotic role of [microRNA-320a] in model systems,” the researchers wrote.

“Investigation of more detailed mechanisms of [microRNA-320a]-mediated regulation of collagen expression may provide new therapeutic strategies for SSc-ILD,” they concluded.