The IgCAM CLMP is required for intestinal and ureteral smooth muscle contraction by regulating Connexin43 and 45 expression in mice

The function of the IgCAM CLMP which is implicated in congenital short-bowel syndrome in humans was studied in mice. Although the levels of mRNAs encoding Connexin43 or 45 are not or only marginally affected, respectively, absence of CLMP caused a severe reduction of both proteins in smooth muscle cells of the intestine and of Connexin43 in the ureter. Analysis of calcium signaling revealed a disordered cell-cell communication between smooth muscle cells which in turn induced an impaired and uncoordinated motility of the intestine and the ureter. Consequently, insufficient transport of chyme and urine caused a fatal delay to thrive, a high rate of mortality and provoked a severe hydronephrosis in CLMP knockouts. Neurotransmission and the capability of smooth muscle cells to contract in ring preparations of the intestine were not altered. Physical obstructions were not detectable and an overall normal histology in intestine as well as in ureter was observed except for a slight hypertrophy of smooth muscle layers. Deletion of Clmp did not lead to a reduced length of the intestine as shown for the human CLMP gene but resulted in gut malrotations. In sum, the absence of CLMP caused functional obstructions in the intestinal tract and ureter by impaired peristaltic contractions most likely due to a lack of gap junctional communication between smooth muscle cells.