Scientists and other healthcare professionals know that obesity is a risk factor for atherosclerosis, which involves narrowing and stiffening of arteries and often leads to hypertension.
However, they know less about the effects of obesity on the small blood vessels around the body, including the brain.
According to a new study, the abnormal growth of small blood vessels in a particular part of the brain may be partly responsible for causing hypertension in people with obesity.
Both kinds of damage — to the large and the small vessels — are recognized factors in the increased risks of disability and mortality associated with obesity.
Older research in mice and humans revealed that eating a high-calorie diet triggers the growth of small blood vessels in the hypothalamus, which is a part of the brain that regulates appetite and blood pressure.
Prof. Cristina García-Cáceres and her colleagues at Helmholtz Zentrum München in Germany set out to discover whether blood vessel growth in the hypothalamus contributes to hypertension.
Rapid effects of a high-calorie diet
When the researchers fed mice a high-fat, high-sugar diet, they found increased growth of blood vessels in the animals’ hypothalamus just 2 weeks later.
This blood vessel growth coincided with weight gain and raised blood levels of leptin, a hormone produced by fat tissue to help regulate long-term food intake.
In further experiments, the researchers used mice that they genetically engineered to have obesity but no leptin. Despite having obesity, these mice did not show any vascular changes in the hypothalamus. Therefore, the researchers suggest that leptin is the key player in mediating vascular changes.
However, when the scientists injected the mice with leptin, the animals lost weight and sprouted more hypothalamic blood vessels.
In further experiments, the researchers showed that star-shaped cells in the hypothalamus called astrocytes mediated this effect.
Astrocytes are support cells that interact with both neurons and blood vessels at the blood-brain barrier.
Leptin induced the cells to produce “vascular endothelial growth factor” (VEGF) and stimulate blood vessel growth.
Crucially, VEGF and the overgrowth of blood vessels in this part of the brain appeared to trigger increased blood pressure in obese mice.
The study appears in the journal Cell Metabolism.
“While previous research has focused primarily on neurons, our research highlights the new role of astrocytes, historically assumed less relevant than neurons, in controlling blood pressure,” he adds.
The scientists note that the principal limitation of their study was that it did not explain how VEGF expression and blood vessel growth in the hypothalamus raises blood pressure.
In addition, as with any animal model of disease, the findings may not translate well to humans with obesity.
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