Platelet-derived growth factor receptor α-positive cells in the tunica muscularis of human colon

Abstract

An obstacle to understanding motor pathologies of the gastrointestinal (GI) tract is that the physiology of some of the cellular components of the gut wall is not understood. Morphologists identified fibroblast-like cells in the tunica muscularis many years ago, but little is known about these interstitial cells because of inadequate techniques to identify these cells. Recent findings have shown that fibroblast-like cells express platelet-derived growth factor receptor α (PDGFRα) in mice and that antibodies for these receptors can be used to label the cells. We used immunohistochemical techniques to study the phenotype and intercellular relationships of fibroblast-like cells in the human colon. Fibroblast-like cells are labelled specifically with antibodies to PDGFRα and widely distributed through the tunica muscularis of human colon. These cells form discrete networks in the region of the myenteric plexus and within the circular and longitudinal muscle layers. Platelet-derived growth factor receptor α(+) cells are distinct from c-Kit(+) interstitial cells of Cajal and closely associated with varicose processes of neurons expressing substance P (excitatory motor neurons) or neuronal nitric oxide synthase (nNOS) (inhibitory motor neurons). Platelet-derived growth factor receptor α(+) cells express small conductance Ca(2+)-activated K(+) channels (SK3), which are likely to mediate purinergic neural regulation of colonic muscles. Our data suggest that PDGFRα(+) cells may have an important role in transducing inputs from enteric motor neurons. This study identifies reagents and techniques that will allow investigation of this class of interstitial cells and help develop an understanding of the role of PDGFRα(+) cells in the human GI tract in health and disease.

Fig 1

Immunolabelling of PDGFRα (green) in the muscle layer of human colon. (A) Circular muscle layer of T colon. (B) Longitudinal muscle layer of A colon. (C) Myenteric plexus region of S colon. PDGFRα⁺ cells were multi-polar cells and interconnected. In circular and longitudinal muscle layer, cell bodies of PDGFRα⁺ cells ran parallel to smooth muscle cells. In myenteric region, PDGFRα⁺ cells formed an extensive fine network. Scale bar is 10 μm in all panels.

Fig 2

Double immunolabelling of PDGFRα (green) and c-Kit (red). (A–C) Circular muscle layer of A colon. (D–F) Myenteric plexus region of S colon. PDGFRα⁺ cells and c-Kit⁺ cells (ICC) formed distinct networks in the same anatomical regions and close relationships with each other. Scale bar is 10 μm in all panels.

Fig 3

Double immunolabelling of PDGFRα (green) (A) and PGP9.5 (red) (B) in the circular muscle layer of T colon. PDGFRα⁺ cells were closely associated with processes of enteric neurons, which express PGP9.5-like immunoreactivity (C). Scale bar is 10 μm in all panels.

Fig 4

Double immunolabelling of PDGFRα (green) (A) and nNOS (red) (B) in the circular muscle of S colon. PDGFRα⁺ cells were closely associated with inhibitory enteric neurons, denoted by the expression of nNOS-like immunoreactivity (C). Fine varicose processes of inhibitory enteric neurons were in close proximity to PDGFRα+ cell processes (arrows in C), suggesting that PDGFRα⁺ cells may have synapse-like communication with these neurons. Scale bar is 10 μm in all panels.

Fig 5

Double immunolabelling of PDGFRα (green) (A) and substance P (red) (B) in the circular muscle layer of A colon. PDGFRα⁺ cells were closely associated with excitatory enteric neurons, denoted by expression of Substance P-like immunoreactivity (C). Fine varicose processes of excitatory enteric neurons were in close proximity to PDGFRα⁺ cell processes (arrows in C), suggesting that PDGFRα⁺ cells may have synapse-like communication with these neurons. Scale bar is 10 μm in all panels.

Fig 6

Double immunolabelling of PDGFRα (green) and SK3 (red). (A–C) Circular muscle layer of T colon. (D–F) Myenteric plexus region of T colon. SK3-like immunoreactivity was expressed in all PDGFRα⁺ cells and was not resolved in other cell types. Scale bar is 10 μm in all panels.