A new mechanism
of blood redistribution that is essential for the proper functioning of the
adult retina has just been discovered in vivo by researchers at the University
of Montreal Hospital Research Centre (CRCHUM).
Their study was published in Nature.
“For the first time, we have identified a
communication structure between cells that is required to coordinate blood
supply in the living retina,” said Dr. Adriana Di Polo, a neuroscience professor
at Université de Montréal and holder of a Canada Research Chair in glaucoma and
age-related neurodegeneration, who supervised the study.
“We already knew that activated retinal areas receive
more blood than non-activated ones,” she said, “but until now no one understood
how this essential blood delivery was finely regulated.”
The study was conducted on mice by two members of Di
Polo’s lab: Dr. Luis Alarcon-Martinez, a postdoctoral fellow, and Deborah
Villafranca-Baughman, a PhD student. Both are the first co-authors of this
study.
In living animals, as in humans, the retina uses the
oxygen and nutrients contained in the blood to fully function. This vital
exchange takes place through capillaries, the thinnest blood vessels in all
organs of the body. When the blood supply is dramatically reduced or cut off —
such as in ischemia or stroke — the retina does not receive the oxygen it
needs. In this condition, the cells begin to die and the retina stops working
as it should.
Tunnelling between cells
Wrapped around the capillaries are pericytes, cells
that have the ability to control the amount of blood passing through a single
capillary simply by squeezing and releasing it.
“Using a microscopy technique to visualize vascular
changes in living mice, we showed that pericytes project very thin tubes,
called inter-pericyte tunnelling nanotubes, to communicate with other pericytes
located in distant capillaries,” said Alarcon-Martinez. “Through these
nanotubes, the pericytes can talk to each other to deliver blood where it is
most needed.”
Another important feature, added Villafranca-Baughman,
is that “the capillaries lose their ability to shuttle blood where it is
required when the tunnelling nanotubes are damaged — after an ischemic stroke,
for example. The lack of blood supply that follows has a detrimental effect on
neurons and the overall tissue function.”
The team’s findings suggest that microvascular
deficits observed in neurodegenerative diseases like strokes, glaucoma, and
Alzheimer’s disease might result from the loss of tunnelling nanotubes and
impaired blood distribution. Strategies that protect these nanostructures
should then be beneficial, but remain to be demonstrated.
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