One of the important processes in
kidney stone development is crystal invasion through extracellular matrix (ECM). Some
proteins in renal tissue or urine have been thought to aggravate crystal invasion. However, this pathogenic mechanism has been previously under-investigated due to a lack of crystal invasion assay. In the present study, we have developed a novel assay for the investigations of
calcium oxalate monohydrate (COM) crystal invasion. Matrix gel was loaded into an in-house migration chamber made on a glass slide to simulate the ECM environment. COM crystals were coated with the tested
protein, which was then bound with
plasminogen. The crystal-
protein-(
plasminogen) complex and
urokinase plasminogen activator (uPA) were placed on-top of the matrix gel. If the tested
protein had
plasminogen-binding capability, the remaining
plasminogen would be activated by uPA to
plasmin, which caused crystal migration through the matrix gel. We then applied this novel assay to evaluate effects of some abundant kidney/urine
proteins (including purified
albumin,
carbonic anhydrase,
lysozyme and
Tamm-Horsfall protein) on COM crystal invasion. The data revealed that
albumin, which is the known
plasminogen-
binding protein, dramatically induced
plasmin activity and crystal invasion, whereas other
proteins had no significant effects as compared to the control. In summary, we have successfully developed a novel assay for the investigations of crystal invasion based on the
plasminogen/
plasmin system. This assay is applicable to examine
proteins that may serve as potential aggravators of crystal invasion and thus will be very useful for further studies on
kidney stone development.