Abstract
Glomerular visceral epithelial cells or
podocytes are located on the outer surface of the
glomerular basement membrane and play an
indispensable role as a filtration barrier. The core
cytoskeleton of the foot processes is actin filaments,
which play an important role in maintaining
the unique structure of podocytes. We previously
established a transgenic mouse line
(NEP25), which expresses human (h)CD25 selectively
on podocytes. By injecting an hCD25-targeted
recombinant immunotoxin (LMB2), podocyte
injury can be induced on demand. After LMB2
injection, NEP25 mice develop nephrotic syndrome
with downregulation of podocyte-specific
proteins. In the present study, we genetically
labeled podocytes with lacZ linked with β-actin-based
CAG promoter. Utilizing the Cre-loxP system,
this labeling was confined to the podocyte
lineage. Without LMB2, all podocytes were positive
for lacZ. After LMB2 injection, lacZ expression
was rapidly downregulated, before podocytes
showed any discernible morphological
changes. Confocal imaging of filamentous (F)-
actin-binding Alexa 488-phalloidin revealed that
the normal continuous pattern of F-actin distribution
in podocytes was punctuated after LMB2
injection. These collectively suggest that disturbance
of actin filaments may be one of the key initial
events leading to subsequent podocyte damage.
