A protein at the center of Parkinson’s disease research now also has been found to play a key role in causing the destruction of bacteria that cause tuberculosis, according to scientists led by UC San Francisco microbiologist and tuberculosis expert Jeffery Cox, PhD.
The protein, named Parkin, already is the focus of intense investigation in Parkinson’s disease, in which its malfunction is associated with a loss of nerve cells. Cox and colleagues now report that Parkin also acts on tuberculosis, triggering destruction of the bacteria by immune cells known as macrophages. Results appear online today (September 4, 2013) in the journal Nature.
The finding suggests that disease-fighting strategies already under investigation in pre-clinical studies for Parkinson’s disease might also prove useful in fighting tuberculosis, according to Cox. Cox is investigating ways to ramp up Parkin activity in mice infected with tuberculosis using a strategy similar to one being explored by his UCSF colleague Kevan Shokat, PhD, as a way to ward off neurodegeneration in Parkinson’s disease.
Globally, tuberculosis kills 1.4 million people each year, spreading from person to person through the air. Parkinson’s disease, the most common neurodegenerative movement disorder, also affects millions of mostly elderly people worldwide.
Cox homed in on the enzyme Parkin as a common element in Parkinson’s and tuberculosis through his investigations of how macrophages engulf and destroy bacteria. In a sense the macrophage — which translates from Greek as “big eater” — gobbles down foreign bacteria, through a process scientists call xenophagy.
Mycobacterium tuberculosis, along with a few other types of bacteria, including Salmonella and leprosy-causing Mycobacterium leprae, are different from other kinds of bacteria in that, like viruses, they need to get inside cells to mount a successful infection.
The battle between macrophage and mycobacterium can be especially intense. M. tuberculosis invades the macrophage, but then becomes engulfed in a sac within the macrophage that is pinched off from the cell’s outer membrane. The bacteria often escape this intracellular jail by secreting a protein that degrades the sac, only to be targeted yet again by molecular chains made from a protein called ubiquitin. Previously, Cox discovered molecules that escort these chained mycobacteria to more secure confinement within compartments inside cells called lysosomes, where the bacteria are destroyed.