Use of p62/SQSTM1 antibodies for neuropathological diagnosis

The demonstration of proteinaceous inclusions in the brain is the key step in the pathological diagnosis of degenerative dementias. The diversity of these diseases has necessitated the use of a panel of (immuno)stains to visualize all suspect pathologies, elevating diagnostic costs. Immunodetection of p62 (sequestosome 1), an abundant constituent in diverse pathological inclusions, holds the potential for a broad-specificity, high-contrast inclusion label. In the brain, pathological p62-positive aggregates comprise both cytoplasmic and nuclear types in neurones and glia, with abnormal tau, alpha-synuclein, TAR DNA-binding protein 43 or polyglutamine proteins as primary components. We therefore set out to evaluate the performance of p62 antibodies for diagnostic immunohistochemistry. We optimized the application conditions and compared the staining profiles of eight commercial p62 antibodies with each other and with reference immunostains, using 2-mm tissue multiarrays representing the major tauo- and synucleinopathies and frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U). The lesions were best visualized using monoclonal antibodies, displaying most types of hallmark inclusions with excellent contrast. Expanding the list of p62-containing aggregates, we demonstrated p62 in tufted astrocytes, coiled bodies, astrocytic plaques, and variform neocortical inclusions and pathological processes in FTLD-U. Polyclonal antibodies exhibited lower sensitivities with variable background levels. We also noted more subtle p62-immunoreactive features lacking overt disease associations. Emphasizing the importance of proper antibody and epitope unmasking methods for maximum sensitivity, we recommend p62 immunodetection as a screening stain for diagnostic practice.