Expression of catalase mRNA and protein in adult rat brain: detection by nonradioactive in situ hybridization with signal amplification by catalyzed reporter deposition (ISH-CARD) and immunohistochemistry (IHC)/immunofluorescence (IF).

Catalase, the classical peroxisomal marker enzyme, decomposes hydrogen peroxide and is involved in the antioxidant defense mechanisms of mammalian cells. In addition, catalase can oxidize, by means of its peroxidatic activity, a variety of substrates such as methanol and ethanol, producing the corresponding aldehydes. The involvement of brain catalase in the oxidation of ethanol is well established, and severe afflictions of the CNS in hereditary peroxisomal diseases (e.g., Zellweger syndrome) are well known. Whereas the distribution of catalase in the CNS has been investigated by enzyme histochemistry and immunohistochemistry (IHC), very little is known about the exact localization of catalase mRNA in brain. Here we report the application of a tyramine/CARD (catalyzed reporter deposition)-enhanced nonradioactive in situ hybridization (ISH) protocol for detection of catalase mRNA in sections of perfusion-fixed, paraffin-embedded rat brain. Catalase mRNA could be demonstrated in a large number of neurons throughout the rat brain as a distinct cytoplasmic staining signal with excellent morphological resolution. Compared to our standard ISH protocol, the CARD-enhanced protocol for catalase mRNA detection in rat brain showed higher sensitivity and significantly better signal-to-noise ratio. In parallel IHC experiments, using an antigen retrieval method consisting of combined trypsin digestion and microwave treatment of paraffin sections, the catalase antigen was found as distinct cytoplasmic granules in most catalase mRNA-positive neurons. In addition, catalase-positive granules, presumably peroxisomes, were found by confocal laser scanning microscopy in glial cells, which were identified by double labeling immunofluorescence for GFAP and CNPase for astroglial cells and oligodentrocytes, respectively. The excellent preservation of morphology and sensitive detection of both mRNA and protein in our preparations warrant the application of the protocols described here for systematic studies of catalase and other peroxisomal proteins in diverse pathological conditions such as Alzheimer's disease and aging.