Summary
Plasmin is the major enzyme that dissolves fibrin in the vasculature and the predominant
source of its zymogen, plasminogen, is liver. However, plasmin has a broad substrate
spectrum and, if present in other tissues, may perform additional functions. We tested
the hypothesis that plasminogen is expressed broadly extrahepatically. A sensitive
and specific isotopic quantitative RT-PCR assay was developed to detect plasminogen
mRNA from total RNA isolated from C57BL/6J mice tissues. Plasminogen mRNA was detected
in adrenal, kidney, brain, testis, heart, lung, uterus, spleen, thymus and gut. Of
these tissues, adrenal had the highest plasminogen mRNA content. In situ hybridization was utilized to localize plasminogen mRNA expressing cell types. Besides
hepatocytes, positive cells were identified in both adrenal and kidney medullae and
cortexes. Plasminogen mRNA expression was detected in cerebral, hippocampal and cerebellar
neurons. Plasminogen mRNA was detected in cells in early stages of spermatogenesis
in testis, present in the cortex and medulla of the thymus and in splenic white and
red pulps. Our results suggest that the plasminogen gene is expressed broadly in extrahepatic
tissues. Thus, tissues separated by local anatomic barriers as well as tissues accessible
to circulating plasminogen have the capacity to provide local sources of plasminogen.
Keywords
Plasminogen - adrenal - brain - testis - thymus