Localization of the lysosomal protease dipeptidyl peptidase II in the young normal rat lens: a correlative light and...

This investigation was follow-up to an earlier biochemical and light microscopic histochemical study, in which the lysosomal protease dipeptidyl peptidase II (DPP II) was demonstrated in rodent lenses. In the present study, a method was employed that allowed a more precise histochemical localization of the enzyme, one that was suitable for ultrastructural as well as light microscopic analysis. Successful demonstration of the enzyme using either of two synthetic substrates, and the significant reduction of the enzyme reaction by phenylmethylsulphonyl fluoride (PMSF), a serine protease inhibitor, pointed to the sensitivity of the method. A flat-embedding technique allowed the correlative light and electron microscopic analysis of specific areas of the specimen. Examination of the epithelium and outer cortical regions of the lens revealed the compartmentalization of DPP II activity within lysosomal dense bodies that were concentrated primarily in the equatorial and sutural regions, and also an association of the reaction product with larger bodies that were confined to the sutural regions. The latter structures appeared to represent fiber cell fragments that were enwrapped with narrow extensions of the surrounding fiber cells. The location of enzyme activity within the sutural bodies and also within the intercellular spaces of the modified fiber cell extensions surrounding these bodies suggested that lysosomal proteases may play a role in the segregation and degradation of specific regions of normal lens fiber cells.