Detection of constitutive and inducible HSP70 proteins in formalin fixed human brain tissue

The investigation of formalin fixed and paraffin embedded tissue is a routine method in forensic histology. Since these samples are usually stored for decades they provide a unique tissue bank for different scientific issues. In the past, numerous studies were conducted using different kinds of paraffin embedded tissues. However, it is well known that formalin affects macromolecules and thus might hamper reliable and reproducible molecular experiments. The aim of this study was to find out if the treatment with formalin has a negative effect on different protein detection methods and additionally to define the dimension of those possible deleterious effects. We incubated brain tissue samples in formalin for up to three months. After incubation, the samples were analyzed using immunohistochemistry (IHC) and Western blotting to specifically detect and quantify members of the HSP70 superfamily (heat shock proteins). Our study shows that the Western blot analysis of formalin fixed tissues does not allow a reliable detection of proteins at all, while a reproducible detection by IHC was still possible after one month of incubation.