Several years ago, a team of NYU Langone Health researchers made a surprising discovery when conducting a gene-deletion study. In mice fed high-fat diets, knocking out the gene RAGE, which was previously linked to diabetic complications, protected the mice from developing both obesity and insulin resistance.
“It was an unexpected result but not inconsistent with the idea that these molecules, which we know are involved in inflammation, would also regulate metabolism,” says Ann Marie Schmidt, MD, the Dr. Iven Young Professor of Endocrinology, who first discovered RAGE, the receptor for advanced glycation end products, nearly three decades ago and now leads RAGE research at NYU Langone.
RAGE as a Metabolic Player
Since then, the team has been studying this link between RAGE and obesity. In March 2017, the American Heart Association (AHA) awarded Dr. Schmidt a $1 million Center grant to support this work as part of the multi-institution AHA Strategically Focused Obesity Research Network Center, a nearly $4 million, 4-year research collaboration between basic, clinical, and population health groups that is under the direction of Dr. Schmidt, Ira J. Goldberg, MD, the Clarissa and Edgar Bronfman, Jr. Professor of Endocrinology and director of the Division of Endocrinology, Diabetes, and Metabolism, and Mary Ann Sevick, MD, professor of population health.
“One question the AHA grant wants answered in both mouse models and human subjects: Is the RAGE mechanism not only suppressing energy expenditure, leading to obesity, but also impairing the ability of patients to achieve and sustain weight loss?” says Dr. Schmidt.
Researchers had long suspected that inflammatory and metabolic pathways are tightly coupled, but what they didn’t know is that RAGE itself is implicated in the process. That discovery, along with related research at other institutions, opened up the possibility of a range of new, targeted treatments for both obesity and one of its key consequences, diabetes (and its complications).
“Today’s therapeutic approaches—managing weight and blood glucose—are largely aimed at tackling the core manifestations of these disorders, but these therapies are often not effective and do not address the fundamental cause,” says Dr. Schmidt. Now her team is specifically trying to understand how molecules that increase in obesity and diabetes bind to RAGE and then signal adverse inflammatory and metabolic effects, which suppress energy expenditure—and how to inhibit these effects and release the brakes on optimal use of energy in obesity and in weight loss.
Targeting the RAGE-DIAPH1 Pathway to Treat Metabolic Disease
There are efforts under way by others to therapeutically inhibit RAGE and the ligands that bind to it in its extracellular regions in order to mimic the deletion effects seen in high-fat-diet mice. So far, the evidence suggests that the role RAGE plays in the human body is predominantly a negative one. “The brand of inflammation that this receptor imparts is not the kind of inflammation that facilitates survival. Rather, it seems to facilitate inexorable tissue damage,” says Dr. Schmidt.
But proving that it doesn’t also serve some unknown important function in the body will take some time. So Schmidt’s team is exploring another approach. Instead of targeting RAGE directly, she is focusing on the intracellular effector DIAPH1, which binds to the RAGE “tail” and is essential for RAGE-mediated signaling—a pathway her team discovered in 2008 and the one that so far seems to be important in transducing the effects of RAGE in inflammation.
In collaboration with Alexander Shekhtman, PhD, professor of chemistry at the University at Albany, Dr. Schmidt used high-throughput assays to screen a library of 58,000 small molecules for any that block RAGE-DIAPH1 interaction. Based on dose-response testing, NMR spectroscopy, and fluorescence-titration experiments, the researchers identified 13 candidates that bind to the site on the RAGE tail so that DIAPH1 can’t. Further studies showed how well these competitive inhibitors blocked signal transduction, cellular migration, and inflammatory gene expression, as well as, ex vivo, ischemia-induced perturbation of heart function and, in vivo, inflammation in both a delayed-type hypersensitivity reaction and upon direct injection of RAGE ligands into normal mice.
“If we’re successful in showing that these molecules work in mice,” says Dr. Schmidt, “we may have the foundation for ways not only to block disadvantageous inflammation that leads to macro- and microvascular diabetes complications but maybe also to facilitate prevention of obesity and to improve metabolic responses in weight loss to mitigate obesity.”