Tiny genetic molecules linked to trachoma scarring, study finds

A certain micro-RNA could be the reason why Chlamydia causes chronic scarring and blindness in some people but not others, according to new research.

A team for the London School of Hygiene and Tropical Medicine, who collaborated with West African colleagues, identified the micro-RNA, known as miRNA-184, in a paper published in BMC Infectious Diseases.

MiRNA-184 is significantly decreased in people who suffer the chronic inflammation that could lead to trachoma, microbial immunity researcher, Dr Martin Holland, said.

Dr Holland told OT that a synthetic version of the micro-RNA could one day be administered to such patients at risk of scarring to prevent irreversible blindness.

In the 51 countries it is endemic in, Chlamydia trachomatis infects the conjunctiva of the eye. Though the infection can be treated with antibiotics, children who experience repeated infections can suffer chronic inflammation and scarring of the eyelids.

Dr Holland said his team’s micro-RNA research aimed to better understand why only some patients experienced trichiasis, when eyelashes turned inward, scratching the cornea and turning it opaque, while others did not.

Micro-RNA strands act as controlling molecules, regulating genetic activity.

The new studies, partly funded by charities Fight for Sight and the Wellcome Trust, looked at the micro-RNA produced in the eye during the initial stages of the disease.

Using RNA sequencing, his team effectively ‘counted’ the number of micro-RNA strands in conjunctival samples in five healthy and five infected children.

They then validated their initial results using quantitative polymerase chain reaction on 163 people’s conjunctival samples.

This data showed that miRNA-184, which plays a role in retinal cells communicating normally, decreased with the severity of the Chlamydia eye infection. Another – miRNA-155 – increased with such inflammation.

Their previous work on trachoma, which has caused 1.2 million people worldwide to lose their sight, had thrown up thousands of different micro-RNA.

Dr Holland said the team’s wider research has now narrowed this number down to four key types, making a very complex picture much simpler. “Hopefully one of these four will have an impact,” he said.

There were exciting developments in using synthetic micro-RNA to treat disease. However, veterinary science, for example, was progressing faster than medical science in this field, Dr Holland explained.

He envisioned, should miRNA-184 or another micro-RNA have potential, a synthetic treatment might one day be offered in the form of an eye drop.

He added: “You wouldn’t want to treat everyone this way. You would identify the inflammation that puts people most at risk and you could treat their inflammation very specifically.”

Dr Holland explained that a number of factors, from the person’s genetics to the virulence of the disease, might impact the levels of micro-RNA in a person’s cell. “You get both internal and external influences,” he said.