Protease-resistant SOD1 aggregates in amyotrophic lateral sclerosis demonstrated by paraffin-embedded tissue (PET) blot

Objectives: The paraffin-embedded tissue (PET) blot technique followed by limited protease digestion has been established to detect protein aggregates in prion diseases, alpha-synucleopathies, and tauopathies. We analyzed whether the scope of the method can be extended to analyze aggregates in mouse and human tissue with amyotrophic lateral sclerosis (ALS) associated with superoxide dismutase 1 (SOD1) mutation. Methods: Formalin-fixed and paraffin-embedded brain and spinal cord tissue from SOD1(G93A) mice was first analyzed for the expression of SOD1, aggregated SOD1, ubiquitin, and p62 by convential immunohistochemistiy and then used to establish the PET blot technique, limited protease digest, and immunodetection of SOD1 aggregates. The method was then transferred to spinal cord from an ALS patient with SOD1(E100G) mutation. Results: Mouse and human paraffin-embedded brain and spinal cord tissue can be blotted to membranes and stained with anti-SOD1 antibodies. The SOD1 labelling is abolished after limited proteolytic digest in controls, whereas under identical conditions SOD1 aggregates are detected the SOD1(G93A) mouse model of ALS and in human familial ALS. The most prominent areas where aggregates could be detected are the brainstem and the anterior horn of the spinal cord. Discussion: Applicability of the PET blot technique to demonstrate SOD1 aggregates in ALS tissue associated with mutations in the SOD1 gene offers a new approach to examine potential spreading of aggregates in the course of ALS.