A mutant collagen XIII alters intestinal expression of immune response genes and predisposes transgenic mice to develop B-cell lymphomas.

Epithelial cells of mucosal surfaces are critical for maintaining immune homeostasis by aiding in the discrimination of pathogenic and commensal microorganisms and modulating the activities of antigen-presenting cells and lymphocytes. Functional breakdowns resulting in chronic infection and inflammation are associated with the development of hematologic and solid neoplasms for which detailed pathogenetic mechanisms are poorly understood. Mice heterozygous for a transgene Col13a1(del) expressing a mutant collagen XIII developed clonal mature B-cell lineage lymphomas originating in mesenteric lymph nodes (MLN). The tumors were associated with T cells and macrophages. The incidence of disease was reduced 2-fold in transgenic mice raised under specific pathogen-free conditions, suggesting a role for infectious agents. The lymphomas did not express the mutant collagen XIII, indicating that its influence on tumorigenesis was B-cell extrinsic and likely to be associated with collagen XIII-positive tissues drained by the MLN. Studies of the small intestines of transgenic mice showed that the subepithelial basement membranes (BM) were highly abnormal and that they exhibited heightened expression of genes involved in immune responses. These results define collagen XIII-dependent maintenance of the intestinal BM as a previously unappreciated component of immune responses and a critical determinant of cancer susceptibility.

Cardiac dysfunction in transgenic mouse fetuses overexpressing shortened type XIII collagen.

Overexpression of type XIII collagen molecules with an 83-amino-acid residue in-frame deletion of part of the ectodomain leads to fetal lethality in Col13a1COL2del transgenic mice. We characterize here the functional disturbances in the cardiovascular system of mouse fetuses overexpressing mutant type XIII collagen. Doppler ultrasonography was performed at 12.5 days of gestation on 33 fetuses resulting from heterozygous matings of seven female mice and on 16 fetuses from two matings between heterozygous and wild-type mice. Nine fetuses had atrioventricular valve regurgitation (AVVR), and all of them were transgene-positive. The fetuses with AVVR had a lower outflow mean velocity (Vmean; P<0.005) and a greater proportion of isovolumetric relaxation time (IRT%) in the cardiac cycle (P<0.0001) than those without AVVR, and their ductus venosus pulsatility indices for veins (DV PIV) and the umbilical artery pulsatility indices were increased. A positive correlation was found between IRT% and DV PIV, and a negative correlation was seen between outflow V(mean) and DV PIV. Morphological analysis of the heart revealed no differences between the two groups of fetuses, but histological analysis showed the trabeculation of the ventricles to be reduced and the myocardium to be thinner in the fetuses with AVVR. Based on in situ hybridization, type XIII collagen mRNAs were normal constituents of these structures. Moreover, a positive correlation was found between outflow Vmean and myocardial thickness. IRT% and DV PIV correlated negatively with myocardial thickness. Thus, overexpression of mutant type XIII collagen results in mid-gestation cardiac dysfunction in mouse fetuses, and these disturbances in cardiac function may lead to death in utero.