Epigenetics and chromatin dynamics: a review and a paradigm for functional disorders

BACKGROUND

Motility and functional gastrointestinal disorders have high prevalence in the community, cause significant morbidity, and represent a major health care burden. Despite major advances in our understanding of the cellular and molecular basis of gastrointestinal neuromuscular functions, many of these diseases still defy mechanistic explanations. The biopsychosocial model underlying the current classification of functional gastrointestinal disorders recognizes and integrates the pathogenetic role of genetic, environmental, and psychosocial factors but has not been associated with specific molecular mechanisms.

PURPOSE

Here, we propose that this integrative function is encoded in the chromatin, composed of the DNA and associated histone and non-histone proteins and non-coding RNA. By establishing epigenetically heritable 'molecular memories' of past stimuli including environmental challenges, the chromatin determines an individual's responses to future insults and translates them into high-order outputs such as symptoms and illness behavior. Thus, surveying epigenetic signatures throughout the genome of affected cells in individual patients may make it possible to better understand and ultimately control the phenomena described by the biopsychosocial model. In this review, we provide a high-level but comprehensive description of the concepts and mechanisms underlying epigenetics and chromatin dynamics, describe the mechanisms whereby the environment can alter the epigenome and identify aspects of functional gastrointestinal and motility disorders where epigenetic mechanisms are most likely to play important roles.

Gastroparesis and functional dyspepsia: excerpts from the AGA/ANMS meeting

BACKGROUND

Despite the relatively high prevalence of gastroparesis and functional dyspepsia, the aetiology and pathophysiology of these disorders remain incompletely understood. Similarly, the diagnostic and treatment options for these two disorders are relatively limited despite recent advances in our understanding of both disorders.

PURPOSE

This manuscript reviews the advances in the understanding of the epidemiology, pathophysiology, diagnosis, and treatment of gastroparesis and functional dyspepsia as discussed at a recent conference sponsored by the American Gastroenterological Association (AGA) and the American Neurogastroenterology and Motility Society (ANMS). Particular focus is placed on discussing unmet needs and areas for future research.

Template switching within exons 3 and 4 of KV11.1 (HERG) gives rise to a 5' truncated cDNA

K(V)11.1 (HERG) channels contribute to membrane potential in a number of excitable cell types. We cloned a variant of K(V)11.1 from human jejunum containing a 171 bp deletion spanning exons 3 and 4. Expression of a full-length cDNA clone containing this deletion gave rise to protein that trafficked to the cell membrane and generated robust currents. The deletion occurred in a G/C-rich region and identical sequence elements of UGGUGG were located at the deletion boundaries. In recent studies these features have been implicated to cause deletions via template switching during cDNA synthesis. To examine this possibility we compared cDNAs from human brain, heart, and jejunum synthesized at lower (42 degrees C) and higher temperatures (70 degrees C). The 171 bp deletion was absent at the higher temperature. Our results suggest that the sequence and secondary structure of mRNA in the G/C rich region leads to template switching producing a cDNA product with a 171 bp deletion.

Pacemaking in interstitial cells of Cajal depends upon calcium handling by endoplasmic reticulum and mitochondria

Pacemaker cells, known as interstitial cells of Cajal (ICC), generate electrical rhythmicity in the gastrointestinal tract. Pacemaker currents in ICC result from the activation of a voltage-independent, non-selective cation conductance, but the timing mechanism responsible for periodic activation of the pacemaker current is unknown. Previous studies suggest that pacemaking in ICC is dependent upon metabolic activity 1y1yand1 Ca2+ release from intracellular stores. We tested the hypothesis that mitochondrial Ca2+ handling may underlie the dependence of gastrointestinal pacemaking on oxidative metabolism. Pacemaker currents occurred spontaneously in cultured ICC and were associated with mitochondrial Ca2+ transients. Inhibition of the electrochemical gradient across the inner mitochondrial membrane blocked Ca2+ uptake and pacemaker currents in cultured ICC and blocked slow wave activity in intact gastrointestinal muscles from mouse, dog and guinea-pig. Pacemaker currents and rhythmic mitochondrial Ca2+ uptake in ICC were also blocked by inhibitors of IP3-dependent release of Ca2+ from the endoplasmic reticulum and by inhibitors of endoplasmic reticulum Ca2+ reuptake. Our data suggest that integrated Ca2+ handling by endoplasmic reticulum and mitochondria is a prerequisite of electrical pacemaking in the gastrointestinal tract.