Distribution of cathepsin D immunoreactivity in the central nervous system of rat and selected brain regions of man

Cathepsin D-mediated proteolysis of apolipoprotein E: possible role in Alzheimer's disease

Proteolysis of apolipoprotein E (apoE) may be involved in the pathogenesis of Alzheimer's disease (AD). We previously identified aspartic protease(s) as possibly contributing to the proteolysis of apoE in human brain homogenates. The current study used biochemical and immunohistochemical methods to examine whether cathepsin D (catD) and cathepsin E (catE), candidate aspartic proteases, may be involved in apoE proteolysis. CatD was found to proteolyze both lipid-free recombinant full-length human apoE and lipidated human plasma full-length apoE (apoE4/dipalmitoylphosphatidylcholine-reconstituted discs). CatE was found to proteolyze lipid-free recombinant human apoE to a much greater extent than lipidated apoE. This proteolysis, as well as proteolysis of human apoE added to brain homogenates from apoE-deficient mice, was inhibited by pepstatin A (an aspartic protease inhibitor), but not by phenylmethanesulfonyl fluoride (a serine protease inhibitor). The major apoE fragment obtained with catD included the receptor-binding domain and had an apparent molecular weight similar to that found in human brain homogenates. There was little immunoreactivity for catE in AD brain tissue sections. In contrast, qualitative and quantitative analyses of immunostained sections of the frontal cortex revealed that catD and apoE are colocalized in a subset of predominantly dense-core neuritic plaques and in some neurofibrillary tangles. A positive correlation was observed between estimated duration of illness and the percentage of apoE-positive plaques that were also catD-positive. These results suggest that aspartic proteases, catD in particular, may be involved in proteolysis of apoE and perhaps contribute to the generation of apoE fragments previously implicated in AD pathology.

Cathepsin D in intestinal ganglion cells. A potential aid to diagnosis in suspected Hirschsprung's disease

There is still a need for a better method of detecting immature ganglion cells in paraffin sections of colorectal luminal biopsies in cases suspected of Hirschsprung's disease. The lysosomal aspartic proteinase cathepsin D has been immunolocalized to various cell types, including ganglion cells. We investigated its expression in intestinal ganglion cells to determine whether it could be used as an aid in the detection of immature ganglion cells in rectal biopsies from children suspected of having Hirschsprung's disease. Routinely processed tissues of eight adult intestines resected for gunshot wounds and six ganglioneuromas (for mature ganglion cells), of six colons resected for neonatal necrotizing enterocolitis (for immature ganglion cells), and of 11 cases of suspected and three cases of known Hirschsprung's disease were immunostained with a polyclonal antibody to cathepsin D using the avidin-biotin-peroxidase method. In all cases, all ganglion cell bodies present showed intense granular cytoplasmic reactivity for cathepsin D. The granules crowded the cytoplasm and formed a collarette around the nucleus. In the submucosa, the only other immunoreactive cells were histiocytes, but they could be distinguished from ganglion cells by their characteristic nuclear features and their occurrence singly and unassociated with nerves. The three resection specimens with Hirschsprung's disease showed a clear transition between the ganglionic and the aganglionic segments. We conclude that cathepsin D is a promising marker of immature ganglion cells in cases suspected of Hirschsprung's disease.

Calpain activity in adult and aged human brain regions

We assayed calpain activity in 27 human brain regions from adult (43-65 years of age) and aged (66-83 years of age) postmortem tissue samples. Calpain I (microM Ca-requiring) activity was 10% or less of the total activity; it was below detectable levels in a number of areas, and so data are are expressed as total (microM + mM Ca-dependent) calpain activity. The distribution of the enzyme was regionally heterogeneous. Highest activity was found in the spinal cord, followed by the amygdala, and levels in mesencephalic areas and in cerebellar grey matter were also high. Levels in cerebellar white matter, tegmentum, pons, and putamen were low, and activity in cortical areas was also relatively low. Although in some areas activity seemed higher with aging, the differences were not statistically significant. We previously found that the regional distribution of cathepsin D in human and in rat brain is similar, this seems to be true for calpain activity as well. The increase of protease activity with age found in rat brain is not found in human areas, as was shown previously with cathepsin D, and in the present study with calpain.

Abnormal distribution of cathepsins in the brain of patients with Alzheimer's disease

Formalin-fixed paraffin-embedded hippocampal sections of brains with early-onset and late-onset Alzheimer's disease were studied immunohistochemically with antisera against cathepsin D and cathepsin B. In addition to the staining of neuronal perikarya, some of the senile plaques visualized by Bielshowsky silver staining and some of reactive astrocytes were positively stained with the antisera against cathepsin D and cathepsin B in brains with Alzheimer's disease. Abnormal localization of cathepsin D and cathepsin B immunoreactivity in neuronal perikarya was observed in brains with early-onset Alzheimer's disease. These findings demonstrate that the distribution of lysosomal proteases was altered in brains with Alzheimer's disease, suggesting the primary and/or secondary involvement of the lysosomal proteases in the pathological process of Alzheimer's disease.

Cell type-specific distribution of cathepsin B and D immunoreactivity within the rabbit retina

The cellular localization of cathepsin B and D immunoreactivity was demonstrated at the light microscopic level in the retina of adult rabbits by use of the peroxidase-antiperoxidase technique. Antisera were raised against rat liver enzymes. Whereas cathepsin D immunoreactivity was confined to Müller (glial) cells, cathepsin B was demonstrated in some, but not all, neuronal cell types. It is proposed that the two enzymes might carry different functions within the neuronal versus glial compartment.

Immunohistochemical detection of cathepsin D in human neuroontogenesis

An antiserum against rat liver cathepsin D, which was previously found to cross-react with human brain cathepsin(s) D, was used to immunolocalize the enzyme in developing CNS man. Cathepsin D protein was found in neurons as well as in glial cells. The aerliest occurrence of cathepsin D was observed in neuroblasts at the 12th gestational week. During pre-, peri-, and postnatal neuroontogenesis, there is a strong increase in the amount of immunoreactive material.

Cathepsin D, B, and H in rat brain as demonstrated by immunohistochemistry

Monospecific antisera against cathepsins B, D, and H were used to immunolocalize these proteinases in neural structures of rat brain. Cathepsins B and D were found to be largely co-localized in nerve cells. Cathepsin H could not be identified by use of immunocytochemistry.