Researchers have identified that low microRNA (miRNA) immunity increases the risk of COVID-19 infection in older adults and people with diabetes.

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MicroRNAs are a key class of gene expression regulators that play an important role in inflammation and immune response. The study led by researchers from Nanjing University in China identified four circulating miRNAs -- miR-7-5p, miR-24-3p, miR-145-5p and miR-223-3p -- which are high in healthy people and much lower in older people and diabetic patients. These miRNAs could effectively inhibit SARS-CoV-2 replication by directly targeting the S protein, said Chen-Yu Zhang from the varsity's School of Life Sciences.

Serum exosomes containing these miRNAs from young people could strongly inhibit SARS-CoV-2 replication, but this inhibitory effect was low in older people and diabetic patients, the researchers said. Long-term exercise was found to increase the level of these miRNAs in the blood offering better protection against the SARS-CoV-2 virus.

The team found that three out of the four circulating miRNAs are significantly increased in the serum of healthy volunteers after 8-weeks' continuous physical exercise. Serum exosomes isolated from these volunteers also showed stronger inhibitory effects on S protein expression and SARS-CoV-2 replication. The study also provides an interesting observation that continuous physical exercise could boost miRNA immunity against SARS-CoV-2, which gives you another reason to hit the gym after work. Working out every day would therefore help all of us, old or young, to stay out of COVID-19's way.

Further, the findings, detailed in the journal Signal Transduction and Targeted Therapy, also demonstrates for the first time that our own endogenous miRNAs could directly inhibit SARS-CoV-2 virus. Previous studies led by the tema have shown that approximately 89 per cent of viruses that infect humans could be targeted by human miRNAs. The new study provides strong and direct evidence supporting the theory that miRNAs, particularly extracellular miRNAs, could function as "RNA defence" and protect cells against foreign nucleic acids, Zhang said.

The study indicates that miRNAs are an important component of the endogenous RNA-based immune system to fight virus infection. This new understanding of miRNA function may provide new perspectives for prevention, surveillance and treatment of COVID-19, Zhang added.