Learning from leprosy’s nerve damage

Since ancient times, societies have feared and sometimes cast out people with leprosy, an infectious disease characterized by skin lesions and a gradual loss of feeling in the limbs. Researchers have now teased out some of the earliest steps in the irreversible nerve damage characteristic of the disease. It turns out that the bacterium that causes leprosy directly damages a protective sheathing, made of the protein myelin, around many nerve cells.

BREAK UP. Top: Intact myelin, shown in red, sheaths nerve cells growing in a laboratory. Bottom: Leprosy-inducing bacteria damage myelin. Rambukkana/Science

The myelin sheath is produced by so-called Schwann cells. The leprosy-causing bacterium–known as Mycobacterium leprae–can attach to all Schwann cells but it can grow only inside those that are not making myelin at the time.

Within a day after the bacteria attach to Schwann cells making myelin along nerves in cell culture, the nerves show significant loss of myelin, Anura Rambukkana of Rockefeller University in New York and his coworkers report in the May 3 Science. A component of the bacterial cell wall continues to induce demyelination even when the bacteria are dead, he says.

“By understanding how this bug causes demyelination directly, we can gain understanding of the early events of demyelination, which we know virtually nothing about,” Rambukkana says. Such knowledge might be important in designing new therapies for leprosy and other diseases, such as multiple sclerosis, that are caused by demyelination, he says.

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