Evidence for an extracellular plasmin-dependent proteolytic system in mineralizing matrices

Area of Science:

• Biochemistry
• Mineralization
• Extracellular Matrix Biology

Background:

• Plasminogen activator (PA) facilitates the conversion of plasminogen to plasmin, a key enzyme in extracellular matrix remodeling.
• PA activity has been observed in various mineralized tissues, but its specific role in dental and bone mineralization remains to be fully elucidated.

Purpose of the Study:

• To identify and characterize plasminogen activator activity within the mineralizing matrices of enamel, dentin, cementum, and bone.
• To investigate the precise localization and potential function of PA during tooth development, particularly in dentinogenesis and enamel mineralization.

Main Methods:

• Fibrinolytic overlay technique to detect PA activity in cell-free mineralizing matrices.
• Immunohistochemical analysis to demonstrate the presence of plasminogen in predentin.
• Extraction and polyacrylamide gel electrophoresis (PAGE) under dissociative conditions to analyze PA properties.

Main Results:

• PA activity was detected in the mineralizing matrices of enamel, dentin, cementum, and bone.
• Predentin was identified as a major site of PA activity, with plasminogen also present.
• PA activity in rodent incisors was localized to a specific zone of enamel mineralization, distinct from the enamel organ.
• Extracted PA from human dentin/predentin showed active forms at Mr 66,000 and 62,000 after PAGE.

Conclusions:

• Plasminogen activator is present in the mineralizing matrices of various hard tissues.
• The localization of PA in predentin and specific enamel zones suggests its involvement in regulating extracellular matrix mineralization.
• Plasmin-dependent proteolysis may play a significant role in the controlled accretion of mineral within dental and bone tissues.