“We’re working with a protein, called serum opacity factor, that has unique characteristics,” said Corina Rosales, PhD, assistant research professor of molecular biology in medicine at the Houston Methodist Research Institute and lead author of the study. “In our experiments, the serum opacity factor reduced cholesterol levels by more than 40 percent in three hours. So this protein is quite potent.”
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The results are published in the Journal of Lipid Research of the American Society for Biochemistry and Molecular Biology.
While this protein’s primary function is to increase bacterial colonization, it also changes the structure of high-density cholesterol-carrying lipoproteins, or HDLs, making it easier for the liver to dispose of the excess cholesterol that prevents fertilization. The researchers also noted that the dramatic action of serum opacity factor on HDL could be used as a potential alternative to statins, which are the current gold standard for lowering cholesterol in people with atherosclerosis.
HDL, known as the “good cholesterol,” carries excess cholesterol from various tissues to the liver for breakdown, lowering cholesterol levels. However, if there is HDL dysfunction, lipid metabolism is altered, which can then be harmful, like its counterpart LDL or low-density lipoprotein. LDL, often referred to as “bad cholesterol,” transports cholesterol from the liver to other tissues, with high levels of it causing accumulation and disease.
“Both HDLs and LDLs contain a mixture of free and esterified cholesterol, and free cholesterol is known to be toxic to many tissues,” said Henry J. Pownall, PhD, a professor of biochemistry in medicine at the Houston Methodist Research Institute and corresponding author. on the study. “So any dysfunction in HDL could also be a risk factor for several diseases.”
To study HDL dysfunction, the researchers worked with preclinical mouse models that had unnaturally high levels of HDL cholesterol in their bloodstream. While this made them ideal for studying atherosclerosis, Rosales noted that these mice were also completely sterile.
“Cholesterol is the backbone of all steroid hormones, and an orchestra of hormones is needed to have a fertile animal,” Rosales said. “We know that the ovaries are studded with receptors for HDL, so HDL metabolism had to play a very important role in fertility for that reason.”
As predicted, when the researchers fed the sterile mice with a lipid-lowering drug, both LDL and HDL cholesterol levels were lowered and the animals were temporarily saved from infertility. Motivated by these results, they turned to the bacterial protein serum opacity factor, which is known to be highly selective for HDL.
“Serum opacity factor is best known in the context of bacterial streptococcal infections where it serves as a virulence factor. But it was also discovered that this protein only responds to HDL and not to LDL or other lipoproteins,” said Rosales. “We hypothesized that administering the serum opacity factor to these mice might also help restore their fertility.”
For their next set of experiments, the team engineered an adeno-associated virus to deliver the serum opacity factor gene to the mice lacking HDL receptors that had high blood cholesterol. When the gene was expressed and the bacterial protein produced, the animals’ HDL cholesterol dropped significantly and their fertility was restored.
Based on these promising preclinical results, the researchers’ next plan is to conduct a clinical study to investigate lipid levels in women undergoing treatments for idiopathic infertility, the underlying causes of which are not fully known. If these patients have high HDL levels, the researchers say serum opacity factor could be a future line of treatment.
“Even if we helped 1 percent of women who are struggling to conceive, it would change their lives, and I think that’s where we can make the most impact with our research,” Rosales said.
This story was published from an agency news agency with no edits to the text. Only the headline has been changed.