Molecular messengers: Decoding a circulatory threat
By Troy Johnson
Peripheral artery disease (PAD) doesn’t typically announce itself in the form of a stroke or heart attack. The signals are far more subtle – feeling the need to rest while climbing a flight of stairs, experiencing a tightening in the calf muscles while taking a walk or a creeping sensation that normal movement is beginning to slip away.
It’s a common circulatory problem, with an estimated 8-12 million Americans affected, and it can lead to severe outcomes, including tissue death and amputation. As common and potentially consequential as PAD may be, the condition’s onset is frequently under-diagnosed by clinicians.
Ahmed Ismaeel, assistant professor of physiology in the College of Veterinary Medicine and principal investigator in its Metabolic Myopathy Lab, is working to change that. In a multi-omics study of the calf muscles of people with PAD published in the Journal of the American Heart Association, Ismaeel and his collaborators mapped how the disease’s stop-and-go blood flow, or ischemia, rewires gene activity. Their investigation pointed to molecular targets that could help patients walk farther while experiencing reduced pain.
“Compared to other vascular diseases, PAD is surprisingly unknown, but it significantly affects quality of life,” said Ismaeel, who joined the Department of Anatomy, Physiology and Pharmacology in Fall 2025. “The most common symptom is walking-induced leg pain, and a lot of times it’s affecting an older population. A lot of times, people just think, ‘I’m getting old, it’s just normal leg pain with aging.’ They don’t realize that it has to do with their blood flow.”
On-off switches and muscle recovery
Historically, PAD has been viewed as a plumbing problem of sorts. Arteries narrowed by plaque buildup reduce blood flow to limbs, usually in the legs, resulting in pain, cramps or numbness during activity. But that perspective proved to be incomplete. Restoring blood flow with procedures like angioplasty doesn’t always fully restore walking ability, and many patients without usual pain still display sharply reduced mobility.
Ismaeel’s interest in PAD offers another example of how research within the College of Veterinary Medicine connects to the concept of “One Health” and yields findings that can advance clinical care of people and animals alike.
“Through this study, you’re trying to build understanding of how the disease is affecting genetic activity,” Ismaeel said. “Within our study, we looked at the same patient before and after surgery. In the last 10 to 20 years, research has shown that one of the big components of the pathology of the disease is muscle damage. That helps explain why some people don’t bounce back even after revascularization.”
To understand what’s happening inside the leg muscles of individuals with PAD, Ismaeel and his colleagues examined tiny chemical tags on DNA called methylation marks. These marks act as on-off switches that help control whether a gene is active or quiet.
The researchers examined calf muscle biopsies from three groups – people without PAD, patients with intermittent muscle pain in the legs sampled before surgery and six months after a revascularization procedure and patients with narrowed or blocked arteries resulting in ulcers, resting pain or gangrene. By combining several types of genetic tests, the team could see which genes were switched on or off and how those switches had been changed by the disease.
Two genes stood out because their activity level closely matched their methylation “switch” settings. One, HIF‑2α, helps cells respond when oxygen is low – a common condition in PAD. The other, FAM20C, also appears to play a role in muscle cell reaction to stress. Seeing these genes change clearly suggests that they may be key players in how PAD damages muscles.
Ismaael and his co-authors also explored potential changes that resulted after blocked leg arteries were reopened. By sampling patients six months after revascularization, they found AP-1 early response genes (FOS/FOSB) remained elevated. That suggests the patients’ recovery clocks run longer than expected, with the body’s muscle repair program continuing long after the restoration of blood flow.
“The ultimate goal of our research is to increase our understanding of the disease and help find new therapeutics,” Ismaeel said.
That includes investigating the patient recovery process. While walking is recommended as the primary exercise treatment for PAD-related mobility impairments, Ismaeel said up to 45 percent of PAD patients do not respond well to that form of intervention.
“We are currently working on figuring out what makes someone a responder versus a non-responder to exercise therapy,” he said. “We think it could be based on differences in their leg muscles that influence their responsiveness to exercise.”
Photo credits: Cynthia Williford-Bean