BOSTON – A multimodal research process has provided clues to the role of angiogenesis in nonalcoholic fatty liver disease (NAFLD) and its more serious cousin, nonalcoholic steatohepatitis (NASH).
In constructing a protocol that began with patients, moved on to bioinformatics and then performed final validation in the petri dish, Savneet Kaur, PhD, and her colleagues were able to identify several angiogenesis genes likely to contribute to the development of NAFLD and NASH.
“We have seen angiogenic mechanisms and angiogenic genes in the pathophysiology of nonalcoholic fatty liver disease,” said Dr. Kaur, professor of biotechnology at Gautam Buddha Medical School, Greater Noida, India, in a video interview at the annual meeting of the American Association for the Study of Liver Diseases.
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Dr. Kaur said that she and her coinvestigators began with a small group of eight patients with NASH, and seven patients with NAFLD, and also with seven healthy control participants. Genetic analysis and comparison of these patients yielded differential expression of certain genes already known to be associated with angiogenesis in the NASH and NAFLD, but not the healthy control participants.
“We did a microarray analysis, a high throughput gene expression study, and then we selected around 25 to 26 genes which were associated with oxidative stress and angiogenesis,” said Dr. Kaur.
For validation of these genes, Dr. Kaur and her associates used a larger study group of about 150 participants, again approximately evenly divided between those with mild NAFLD, those with more severe steatohepatitis, and healthy controls. “We validated the angiogenic genes in the subject group, and found that around 13 genes are preferentially expressed.”
“About 13 genes including VEGFR1, PIK3CA, CXCL8, NOS3, EREG, CCL2, PRKCE, PPar-gamma, PROK2, RUNX1, SIRT1, HMOX1 and CXCR4 showed significantly different gene expression in the [reverse transcription–polymerase chain reaction] analysis in Gr3 as compared to Gr1 (P less than .05 for each), whereas genes such as PIK3CA, CXCL8, NOS3, CCL2, PROK2, RUNX1, and HMOX1 were differentially expressed in Gr3 in comparison to Gr2 (P less than .05 each). A few genes, PPar-gamma, SIRT1, VEGFR1, HMOX1, PIK3CA, CXCR4, PROK2, and CCL2, showed correlations with fibrosis scores, angiogenesis scores, and NAFLD activity scores of the patients,” wrote Dr. Kaur and her colleagues in the abstract accompanying the poster presentation.
Taking these candidate genes, Dr. Kaur and her colleagues conducted a bioinformatics analysis to determine which transcription factors were controlling the genes. “We wanted to study the pathway – the mechanisms – to determine the upregulation and downregulation of these genes,” said Dr. Kaur.
Finally, Dr. Kaur and her associates took an in vitro approach, using human steatotic hepatocytes and endothelial cells, since “angiogenesis is a property of endothelial cells.” The two types of cells were cultured together, and angiogenic function and gene expression were examined, and checked against the genes and pathways identified in the first two steps. They again saw expression of the angiogenic pathways in the cell culture model. This was consistent with what is seen in patients with NAFLD and NASH: “Definitely, there’s an increase in angiogenesis. There’s an increase in the endothelial cell proliferation, with more fat, more steatosis in the patients,” said Dr. Kaur. Some genes, said Dr. Kaur, are “really important” to this process. Her group is now investigating how the genes are regulated, in order to understand better the precise role of angiogenesis in steatohepatitis.
The study was part of a joint Indo-German project, and sponsored by the Indian Council for Medical Research and the German Federal Ministry of Education and Research. Dr. Kaur reported no relevant conflicts of interest.
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