From BBC

[Guest guest]

HIV's double hit on brain cells

The protein is found on the coating of the virus

HIV can trigger learning and memory deficits by launching a double

attack on the brain, research shows.

It was already known that a protein on the surface of the virus

could kill off mature brain cells.

But the latest study shows it also prevents the production of

replacements by crippling cells with the potential to step in and

take their place.

The University of California at San Diego study appears in the

journal Cell Stem Cell.

The HIV protein both causes brain injury and prevents its repair

Dr Marcus Kaul

The researchers hope their work, which was carried out on mice, will

aid efforts to find new ways to combat HIV-associated dementia.

Researcher Dr Marcus Kaul said: " It's a double hit to the brain.

" The HIV protein both causes brain injury and prevents its repair. "

The success of antiretroviral therapies in keeping " viral load " down

has helped to reduce the severity of HIV-associated dementia in

recent years.

However, the condition is becoming more common as people with HIV

are living longer.

Part of the problem is that anti-HIV drugs find it tough to enter

the brain.

Disrupted chemistry

The researchers had already shown that a protein called gp120, which

is found on HIV's outer coating, can kill off brain cells by

disrupting their internal chemistry.

In the latest study, they showed that gp120 also slows production of

new brain cells in the hippocampus, a brain region central to

learning and memory.

Under normal circumstances, these newborn cells become integrated

into existing brain circuits and are thought to contribute to

certain forms of learning and memory.

It appears the same chemical disruption that kills cells is also

responsible for blocking production of replacements.

Dr Kaul said: " This indicates that we might eventually treat this

form of dementia by either ramping up brain repair or protecting the

repair mechanism. "

Alcorn, senior editor of the HIV information service NAM,

said: " The discovery that HIV affects stem cell proliferation in the

brain is bound to add to concerns that people with HIV doing well on

antiretroviral therapy may nevertheless face a higher risk of

dementia in years to come.

" Antiretroviral drugs have lowered viral load so that HIV will not

kill cells directly, but we don't know the consequences for brain

functioning of a long-term low level of infection.

" It may be that low level infection is enough to interfere with the

regeneration pathways in the way shown in this experiment. "

Griffiths, clinical director at the HIV charity Terrence

Higgins Trust said: " This is fascinating research, but at an

extremely early stage.

" It may well produce benefits for people with HIV, but that is still

some years away. "