Detection of tissue transglutaminase with new antibodies in immunohistochemistry

Abstract

Background: Tissue transglutaminase (tTG) is the most abundantly expressed transglutaminase (TG) enzyme in the human brain. There are some indications for the participation of tTG in the development of neurodegenerative diseases, including Alzheimer’s and Parkinson’s disease. In brain, tTG is known to be expressed in neurons and astroglia (Wilhelmus et al. 2008). Previous data showed tTG being involved in cross-linking s-amyloid and tau and therefore contributing to the development of Alzheimer’s disease hallmarks. It has been observed that neurofibrillary tangles and s-amyloid in senile plaques show immunoreactivity for tTG (Wilhelmus et al. 2008). Furthermore it has been described that transglutaminase activity is increased in Alzheimer’s disease (e.g. Wang et al. 2008). Methods: We tested 12 new monoclonal antibodies with specific reactivity to human tTG (Wolf et al. 2011) on tissue samples of AD brains and age-matched controls. tTG immunoreactivity was compared to tau an amyloid pathology. Additionally we compared our results to those of assays for specific determination of either tTG protein or in-vitro activatable tTG made of adequate regions. Results: The monoclonal antibodies against human tTG showed different immunoreactivity in human brain tissue. Some of them show clear distribution patterns, different in AD brains and controls. Concerning AD pathology we observed a high density of tTG in neurofibrillary tangles and a clear colocalization of tTG and anti-phosphotau antibody. In senile plaques only a light shade of tTG immunoreactivity could be detected with nickel enhanced diaminobenzidine reaction. Some of the antibodies detect tTG associated with reactive Astroglia around senile plaques. Conclusions: Some of the new anti-human tTG antibodies clearly visualize distribution and density of substrate-associated tTG in human brain. The further characterization of their specificity and detected epitopes is just in process. In AD brain, the different density of tTG in aggregated tau and s-amyloid may be caused due to the different concentrations of lysine in tau and s-amyloid peptides. Together with the results of quantification of tTG total protein and activity assays, the new antibodies may contribute to further investigation of tTG in human brain and their role in the development of neurodegenerative diseases like AD.