A groundbreaking set of studies has
found that blocking certain receptors in the brain leads to the growth of
remarkably strong bones. Could a new osteoporosis treatment be on the horizon?
Primarily a disease of
old age, osteoporosis can
cause bones to become gradually weaker.
Over time, bones
become so porous that minor impacts — even just a cough or a sneeze — might
cause fractures.
According to the
Centers for Disease Control and Prevention (CDC), osteoporosis affects
almost 1 in 4 women aged 65
and over in the United States.
As it stands, there is
no cure; treatment focuses on reducing the risk of
fractures but cannot slow the condition's progression.
In a healthy person,
the body breaks down old or damaged bone and replaces it with new bone.
However, as we age,
this cycle becomes off-kilter, and the body breaks down more bone than can be
remade. This leads to progressively weaker bones and, eventually, osteoporosis.
A new role for
estrogen
Estrogen has
a wide range of functions in the human body, particularly regarding
reproduction. The hormone also works in the brain, but scientists currently
know little about its functions there.
Recently, scientists
from the University of California, San Francisco and the University of
California, Los Angeles ran a series of studies to learn more about estrogen in
the brain.
Along
the way, they made a serendipitous discovery that could change the face of
osteoporosis research.
Led by senior study
author Holly Ingraham, Ph.D., the researchers were primarily interested in how
estrogen's activity in the brain alters metabolism during different stages of
life.
In particular, they
were looking at the function of estrogen-sensitive neurons in the hypothalamus.
This is a part of the brain that links the nervous system to the endocrine
(hormone) system.
The hypothalamus plays
an important role in regulating metabolic processes, such as by helping control
body temperature, hunger, sleep, fatigue, and circadian rhythms.
Blocking estrogen in
the brain
The scientists blocked
the effects of estrogen in the hypothalamus of animals. When they did this, the
animals gained weight and became less active.
Initially, the
scientists assumed that the additional weight would be accounted for by extra
fat or muscle tissue.
However, upon further
inspection, they found that the extra weight was due to increased bone mass.
Some of the animals had increased their total bone mass by 800 percent.
"I was immediately struck by the size of the effect. The two
groups didn't overlap at all, which I had never seen. We knew right away it was
a game changer and a new, exciting direction with potential applications for
improving women's health."
Researcher Stephanie Correa, Ph.D.
When the investigators tested the dense mouse bones, they found
that they were also particularly strong. In fact, according to Ingraham:
"Our collaborators
who study bone for a living said they'd never seen bone this strong."
They have now published their findings in the journal Nature
Communications. As Ingraham goes on to say, "Our current understanding
of how the body controls bone growth can't explain this."
"[This] suggests," she adds, "we may have
uncovered a completely new pathway that could be used to improve bone strength
in older women and others with fragile bones."
In follow-up studies, the researchers focused on a particular
region of the hypothalamus that seemed to be having this incredible effect on
bone: the arcuate nucleus.
Since removal of estrogen receptors in this region causes bone
growth, they believe that normally, these cells siphon energy and resources
away from bone growth to be used elsewhere in the body.
This finding is exciting and surprising and only appeared in
female mice.
"Most neuroscientists limit studies to male mice, and few study
estrogen, which may explain why this had never been seen before."
Holly Ingraham, Ph.D.
She continues, "I've always been interested in how sex
hormones make male and female brains different, and this is a really wonderful
example of how dramatic those differences can be."
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