The critical role of muscularis macrophages in modulating the enteric nervous system function and gastrointestinal motility.

Macrophages are the originators of inflammatory compounds, phagocytic purifiers in their local environment, and wound healing protectors in oxidative environments. They are molded by the tissue milieu they inhabit, with gastrointestinal (GI) muscularis macrophages (MMs) being a prime example. MMs are located in the muscular layer of the GI tract and contribute to muscle repair and maintenance of GI motility. MMs are often in close proximity to the enteric nervous system, specifically near the enteric neurons and interstitial cells of Cajal (ICCs). Consequently, the anti-inflammatory function of MMs corresponds to the development and maintenance of neural networks in the GI tract. The capacity of MMs to shift from anti-inflammatory to proinflammatory states may contribute to the inflammatory aspects of various GI diseases and disorders such as diabetic gastroparesis or postoperative ileus, functional disorders such as irritable bowel syndrome, and organic diseases such as inflammatory bowel disease. We reviewed the current knowledge of MMs and their influence on neighboring cells due to their important role in the GI tract.

The Crucial Role of the Interstitial Cells of Cajal in Neurointestinal Diseases.

Neurointestinal diseases result from dysregulated interactions between the nervous system and the gastrointestinal (GI) tract, leading to conditions such as Hirschsprung's disease and irritable bowel syndrome. These disorders affect many people, significantly diminishing their quality of life and overall health. Central to GI motility are the interstitial cells of Cajal (ICC), which play a key role in muscle contractions and neuromuscular transmission. This review highlights the role of ICC in neurointestinal diseases, revealing their association with various GI ailments. Understanding the functions of the ICC could lead to innovative perspectives on the modulation of GI motility and introduce new therapeutic paradigms. These insights have the potential to enhance efforts to combat neurointestinal diseases and may lead to interventions that could alleviate or even reverse these conditions.

Hypoxia-Inducible Factor 1α Stabilization Restores Epigenetic Control of Nitric Oxide Synthase 1 Expression and Reverses Gastroparesis in Female Diabetic Mice.

BACKGROUND & AIMS: Although depletion of neuronal nitric oxide synthase (NOS1)-expressing neurons contributes to gastroparesis, stimulating nitrergic signaling is not an effective therapy. We investigated whether hypoxia-inducible factor 1α (HIF1A), which is activated by high O2 consumption in central neurons, is a Nos1 transcription factor in enteric neurons and whether stabilizing HIF1A reverses gastroparesis. METHODS: Mice with streptozotocin-induced diabetes, human and mouse tissues, NOS1+ mouse neuroblastoma cells, and isolated nitrergic neurons were studied. Gastric emptying of solids and volumes were determined by breath test and single-photon emission computed tomography, respectively. Gene expression was analyzed by RNA-sequencing, microarrays, immunoblotting, and immunofluorescence. Epigenetic assays included chromatin immunoprecipitation sequencing (13 targets), chromosome conformation capture sequencing, and reporter assays. Mechanistic studies used Cre-mediated recombination, RNA interference, and clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9)-mediated epigenome editing. RESULTS: HIF1A signaling from physiological intracellular hypoxia was active in mouse and human NOS1+ myenteric neurons but reduced in diabetes. Deleting Hif1a in Nos1-expressing neurons reduced NOS1 protein by 50% to 92% and delayed gastric emptying of solids in female but not male mice. Stabilizing HIF1A with roxadustat (FG-4592), which is approved for human use, restored NOS1 and reversed gastroparesis in female diabetic mice. In nitrergic neurons, HIF1A up-regulated Nos1 transcription by binding and activating proximal and distal cis-regulatory elements, including newly discovered super-enhancers, facilitating RNA polymerase loading and pause-release, and by recruiting cohesin to loop anchors to alter chromosome topology. CONCLUSIONS: Pharmacologic HIF1A stabilization is a novel, translatable approach to restoring nitrergic signaling and treating diabetic gastroparesis. The newly recognized effects of HIF1A on chromosome topology may provide insights into physioxia- and ischemia-related organ function.

Insulin-Like Growth Factor1 Preserves Gastric Pacemaker Cells and Motor Function in Aging via ERK1/2 Activation.

BACKGROUND & AIMS: Impaired gastric motor function in the elderly causes reduced food intake leading to frailty and sarcopenia. We previously found that aging-related impaired gastric compliance was mainly owing to depletion of interstitial cells of Cajal (ICC), pacemaker cells, and neuromodulator cells. These changes were associated with reduced food intake. Transformation-related protein 53-induced suppression of extracellular signal-regulated protein kinase (ERK)1/2 in ICC stem cell (ICC-SC) cell-cycle arrest is a key process for ICC depletion and gastric dysfunction during aging. Here, we investigated whether insulin-like growth factor 1 (IGF1), which can activate ERK in gastric smooth muscles and invariably is reduced with age, could mitigate ICC-SC/ICC loss and gastric dysfunction in klotho mice, a model of accelerated aging. METHODS: Klotho mice were treated with the stable IGF1 analog LONG R3 recombinant human (rh) IGF1 (150 µg/kg intraperitoneally twice daily for 3 weeks). Gastric ICC/ICC-SC and signaling pathways were studied by flow cytometry, Western blot, and immunohistochemistry. Gastric compliance was assessed in ex vivo systems. Transformation-related protein 53 was induced with nutlin 3a and ERK1/2 signaling was activated by rhIGF-1 in the ICC-SC line. RESULTS: LONG R3 rhIGF1 treatment prevented reduced ERK1/2 phosphorylation and gastric ICC/ICC-SC decrease. LONG R3 rhIGF1 also mitigated the reduced food intake and impaired body weight gain. Improved gastric function by LONG R3 rhIGF1 was verified by in vivo systems. In ICC-SC cultures, rhIGF1 mitigated nutlin 3a-induced reduced ERK1/2 phosphorylation and cell growth arrest. CONCLUSIONS: IGF1 can mitigate age-related ICC/ICC-SC loss by activating ERK1/2 signaling, leading to improved gastric compliance and increased food intake in klotho mice.

Cellular Senescence, Inflammation, and Cancer in the Gastrointestinal Tract.

Due to modern medical advancements, greater proportions of the population will continue to age with longer life spans. Increased life span, however, does not always correlate with improved health span, and may result in an increase in aging-related diseases and disorders. These diseases are often attributed to cellular senescence, in which cells become disengaged from the cell cycle and inert to cell death. These cells are characterized by a proinflammatory secretome. The proinflammatory senescence-associated secretory phenotype, although part of a natural function intended to prevent further DNA damage, creates a microenvironment suited to tumor progression. This microenvironment is most evident in the gastrointestinal tract (GI), where a combination of bacterial infections, senescent cells, and inflammatory proteins can lead to oncogenesis. Thus, it is important to find potential senescence biomarkers as targets of novel therapies for GI diseases and disorders including cancers. However, finding therapeutic targets in the GI microenvironment to reduce the risk of GI tumor onset may also be of value. This review summarizes the effects of cellular senescence on GI aging, inflammation, and cancers, and aims to improve our understanding of these processes with a goal of enhancing future therapy.