Expression of type VI collagen mRNAs in human endometrium during the menstrual cycle and first trimester of pregnancy.

The pattern of type VI collagen deposition in human endometrium throughout the menstrual cycle and in decidua of the first trimester of pregnancy was studied. Immunohistochemical analysis demonstrated a dense microfibrillar network of collagen VI in the stroma of preimplantation endometrium which was reduced during the peri-implantation period and no longer detected in first trimester decidua. However, type VI collagen was consistently present within blood vessel walls in both endometrium and decidua. Using in situ hybridization, mRNAs encoding alpha 1(VI), alpha 2(VI) and alpha 3(VI) chains within endometrial stromal and vascular cells were identified. All three mRNA species are abundant in the villous mesenchyme of the first trimester placenta. The detection of collagen VI mRNA species in the endometrium throughout the menstrual cycle suggests that the apparent decrease in abundance of extracellular immunoreactive fibrils may be a consequence of translational control, matrix redistribution or turnover. In contrast, in the first trimester of pregnancy, collagen VI protein was mainly absent from the decidual stroma and amounts of mRNA were very low, indicating a significant reduction in production. Loss of stromal type VI collagen contributes to the remodelling of the maternal extracellular matrix of pregnancy.