The Pothoulakis Lab Was Highlighted in the Winter 2018 issue of Beyond the Scope
One of the fastest-growing areas of biomedical science is the field of epigenetics — alterations in gene expression that do not involve changes in the DNA. These environmentally induced modifications are of particular interest to investigators looking to find effective new strategies for treating inflammatory bowel disease (IBD). In the laboratory of Charalabos “Harry” Pothoulakis, MD, the Eli and Edythe Broad Chair in Medicine and director of basic research for the UCLA Center for Inflammatory Bowel Diseases in the Vatche and Tamar Manoukian Division of Digestive Diseases, one of the major areas of focus is on a key player in the epigenetic response, microRNAs — small RNA molecules capable of regulating the function of multiple genes.
Dr. Pothoulakis and his colleagues are international leaders in describing the role of microRNAs in IBD, and have developed strategies that show promise in being transferred to the clinic. At the UCLA Center for Inflammatory Bowel Diseases, researchers focus on multiple aspects of IBD pathophysiology, diagnosis and therapy. This includes the role of neuropeptides and hormones in the mediation of inflammation and post-inflammation healing in IBD and the role of fat in the obese state in IBD pathogenesis — given that neuropeptides and hormones regulate appetite and metabolism, and their interactions with fat tissue represent important components of the inflammatory response in IBD. The laboratory of Dr. Pothoulakis is also a world leader in studying the importance of microRNA-related changes in the IBD intestine and the importance of neuropeptides to this process, working closely with researchers in the UCLA Center for Systems Biomedicine, which is also part of the division.
“MicroRNAs are a very clever way for the host to inhibit the function of our genes,” Dr. Pothoulakis explains. He notes that scientists now understand the role of approximately 25,000 genes in the human body, and antagonists to these genes have been developed to inhibit their expression when they go awry. “We have only about 1,500 microRNAs to regulate these 25,000 genes,” Dr. Pothoulakis says. “So if we can use technologies that can inhibit certain microRNAs — or, when desirable, overexpress them, depending on the gene or genes they regulate — we are able to alter the inflammatory response.”
Nearly a decade ago, researchers found altered expression of microRNAs in tissues of patients with IBD. Dr. Pothoulakis was a pioneer in linking microRNA expression with neuropeptides and hormones known to be involved in the inflammatory response. His research group then led the way in showing the therapeutic potential — demonstrating that inhibiting or overexpressing these microRNAs can tamp down the inflammatory response, as well as identifying the downstream targets of these activities.
More recently, Dr. Pothoulakis and colleagues have identified several microRNAs that are activated in the colonic mucosa of IBD patients in response to certain neuropeptides and hormones. They have made oligonucleotide-based, chemically-modified antagonists to these microRNAs and have shown in an IBD animal model that when introduced into the colon, blocking these microRNAs can inhibit the inflammatory response. They have also produced data supporting the efficacy of these antagonists in human biopsies — a critical step on the way to clinical trials with IBD patients.
Publishing in the journal Gut in 2015, Dr. Pothoulakis’ group demonstrated that the microRNA 133α is over-expressed in the colonic tissues of ulcerative colitis patients, and that it regulates the inflammatory signaling of neurotensin, a neuropeptide associated with colonic inflammation. This suggested that targeting the microRNA 133α could be an effective new strategy for a subset of IBD patients. Then in 2016, Dr. Pothoulakis and colleagues described in the Journal of Immunology a second important microRNA in IBD, microRNA-210, that plays a pro-inflammatory role in the development of colitis. The researchers found a network by which neurotensin regulates microRNA-210 as well as angiogenesis, an important aspect of the inflammatory response of IBD patients. This observation provided an additional therapeutic target.
Dr. Pothoulakis’ lab has also found that another neuropeptide, substance P, which mediates both pain and inflammation in humans, plays a critical role in the development of colitis. Reporting in Cellular and Molecular Gastroenterology and Hepatology in 2015, his group showed that when microRNA 221-5p is overexpressed by substance P, it targets the interleukin-6 receptor and, as a result, inhibits the inflammatory response. “All of these studies suggest that as we come up with specific microRNAs that are regulated differentially in IBD, we can either inhibit them if they promote colitis, as in the case of 133α and 210, or promote overexpression when they inhibit colitis, as in the case of 221-5p,” Dr. Pothoulakis explains.
“The advantage of our approach is that by giving an oligonucleotide-based antagonist intra-colonically (enema) to block or promote these microRNAs, we most likely can avoid the side effects associated with most of our current IBD therapies, which tend to be absorbed into the general circulation,” Dr. Pothoulakis adds. In addition, he notes, the strategy offers the potential for IBD clinicians to move toward precision medicine by looking at the biopsies of patients to see whether they have increased expression of these microRNAs, then using the antagonists only in the patients who have elevated levels — thus stratifying patients into groups where they are most likely to have a high rate of therapeutic response. “We are very encouraged by the response we are getting when we inhibit these microRNAs in IBD animal models and in human cells from the biopsies of patients,” Dr. Pothoulakis says. “This appears to be an approach with great potential for translation to the clinic.”