Mitochondrial mechanisms of epigenetic dysregulation in diabetic gastroparesis
Disordered control of smooth muscle function is common in gastrointestinal diseases, which cost billions of dollars in health care spending each year. Gastroparesis is one of the most significant manifestations of gastrointestinal dysmotility, particularly in patients with diabetes mellitus. However, therapeutic options are limited reflecting incomplete understanding of cellular dynamics within the neuromuscular compartment. Previous research has identified interstitial cells of Cajal (ICC) as the cell type most commonly affected in gastroparesis. ICC serve as the physiological pacemaker for phasic contractile activity and may partially mediate cholinergic excitatory and nitrergic inhibitory neuromuscular neurotransmission. Diabetic ICC depletion may arise from reduced Kit signaling, oxidative stress and macrophage action. A critical gap in our knowledge is the lack of understanding of the fate of ICC lost from these insults. Therefore, our main goal is to identify ICC fates, their mechanisms and reversibility in diabetes. Using Cre-loxP technology-based genetic lineage tracing, we have recently determined that in mice during the first 3-5 months of postnatal life, nearly one-third of ICC dedifferentiate and survive as cells lacking, or expressing very low levels of, the key ICC receptor tyrosine kinase Kit. The same approach also detected abundant Kit(low/-) cells genetically traceable from Kit(high) ICC in streptozotocin-diabetic mice, indicating the existence of a cell population from which ICC can potentially re-differentiate. Our central hypothesis is that this phenotypic ICC loss arises, in part, from inhibition of “erasers” of key repressive epigenetic marks due to disturbed mitochondrial metabolism. These changes then lead to silencing of genes critical for ICC identity including Kit. In this pilot project we aim to generate data supporting the role of succinate, a tricarboxylix acid cycle metabolite that accumulates in diabetic tissues, in the epigenetic repression of Kit and other ICC genes. We will employ RNA interference, in-vivo Cre-mediated genome editing and epigenomic and phenotyping methods including the analysis of genomic distribution of histone and DNA marks in relation to ICC gene expression. To facilitate translation of our findings, we will also attempt to restore ICC using epigenetic drugs already approved for use in humans. The concept of manipulating interstitial cell populations via epigenetic reprogramming of cells with persistently altered transcriptional programs will change how we think about neuromuscular plasticity in health and disease.