Immunohistochemical localization of the metalloproteinase meprin in salivary glands of male and female mice.
Meprin is a membrane-bound metalloproteinase which is expressed at high levels in the brush border membrane of proximal tubules of kidneys of some mouse strains (referred to as high meprin-activity mice). The mature active proteinase is not present in kidneys of many inbred strains of mice; however, these low meprin-activity mice possess a kidney protein that crossreacts with polyclonal antibodies prepared against meprin. In the present studies, immunohistochemical methods were used to determine the presence of meprin in liver, pancreas, spleen, testis, thymus, kidney, salivary glands, stomach, duodenum, and skin. Meprin crossreactivity was observed only in kidney and salivary glands. In salivary glands, the enzyme was found on the luminal surface of intercalated and striated ducts of submandibular and parotid glands and on interlobular ducts of the latter. In both kidney and salivary glands, the intensity of immunochemical staining was greater in males compared with females. For both sexes, immunoreactivity was markedly greater in the high meprin-activity mice compared to the low meprin-activity mice. These studies indicate that meprin has a limited tissue distribution, and that genetic and hormonal factors that regulate the proteinase are similar in kidney and salivary glands. The localization of the proteinase implies that the enzyme functions in modifying proteins and peptides that are secreted or re-absorbed in the ducts of these tissues.