Digestive Diseases

Feb. 24, 2024

Although frequently associated with diabetes, the majority of gastroparesis cases remain idiopathic. About a decade ago, researchers noted that the loss of interstitial cells of Cajal (ICCs) might be linked to the cellular pathophysiology underlying gastroparesis. More recently, researchers have begun examining the role of the immune system and its dysregulation in gastroparesis. Observations in animal models suggested that immune cells play a critical role in maintaining and protecting enteric neuronal and ICC function, which can affect motility in the gastrointestinal tract.

In a study conducted by Madhusudan (Madhu) Grover, M.B.B.S., Mayo Clinic colleagues and others from the National Institutes of Health Gastroparesis Clinical Research Consortium (NIH GpCRC), the researchers profiled the human gastric muscle immunome in patients with idiopathic gastroparesis (IG). The results of that study were published in iScience in 2024, with Dr. Grover, a gastroenterologist and researcher at Mayo Clinic in Minnesota, serving as corresponding author.

Study methods

Dr. Grover notes that prior research efforts using bulk RNA-sequencing analysis as well as proteomics of gastric muscle tissue revealed evidence of macrophage-based immune dysregulation in patients with IG.

"Multiple studies have suggested that muscularis macrophages have an important role in maintaining peristaltic motility and in preventing neuronal loss in response to pathogen-mediated injury," explains Dr. Grover. "The aim of our study was to characterize the immune cell populations in human gastric muscle and determine changes in patients with idiopathic gastroparesis. We sought to create an atlas of the types of macrophages and other immune cells in the muscularis propria of the human stomach."

In this study funded by the NIH GpCRC, the researchers performed single-cell sequencing on 26,000 CD45-positive cells from gastric muscle tissue obtained from 20 study participants — seven individuals with IG (the IG group) and 13 individuals without IG (the control group).

Results

Dr. Grover and co-authors note that the study yielded multiple findings that broaden the understanding about the immune system in the gastric muscle layers as well as changes in IG.

• The researchers identified 11 clusters of immune cells in gastric muscle tissue, with T cells (~ 45% of overall cells) and myeloid cells (~ 27%) constituting the largest compartments.
• The proportions of cells belonging to the 11 clusters were similar in participants from the IG and control groups. However, differential expression analysis showed cell subsets containing from 578 to 11,429 differentially expressed genes in nine of the 11 clusters.
• IG group participants had muscularis macrophages (MMs) with decreased expression of tissue-protective and microglial genes and increased expression of monocyte trafficking and stromal activating genes.
• IG group participants had enriched cell signaling pathways, including interleukin-12-mediated Janus kinase signal transducer and activator of transcription signaling, involved in the activation of tissue-resident macrophages, and Eph-ephrin signaling, involved in monocyte chemotaxis.
• IG group participants had a greater abundance of monocyte-like cells in the tissue, suggesting increased trafficking.

"Overall, these data advance the understanding of IG," explains Dr. Grover. "The atlas created will be helpful for other researchers and will allow additional studies of other immune cells as well as understanding of signaling between immune and nonimmune cells in the gastric muscle layers. Until now, the immune cell compartment within the muscle layers of human stomach was not characterized. The study expands our understanding of canonical gene markers for various immune cell types, which acts as a resource for the research community. From the standpoint of IG, this study paves the way for therapeutic targets."

Next steps

Dr. Grover notes that additional research is needed to address study size and other limitations, and to explore the implications of these findings more fully. "Future efforts will need to understand the protein expression and distribution of various cell types, as well as in vitro experiments to examine interactions between immune cells and cells like ICC and enteric nerves that directly regulate the gastric motor function," says Dr. Grover.

For more information

Chikkamenahalli LL, et al. Single cell atlas of human gastric muscle immune cells and macrophage-driven changes in idiopathic gastroparesis. iScience. In press.

Refer a patient to Mayo Clinic.