Optimized Immunohistochemical Detection of Rat ESR2 Proteins Using the Specific Anti-ESR2 Monoclonal Antibody PPZ0506

Abstract Background: Research on ESR2, also known as estrogen receptor β (ERβ), is a notorious example of data distortion due to the use of inadequately validated antibodies. Although the absence of reliable specific antibodies against ESR2 has severely hindered the promotion of ESR2 research, a specific anti-human ESR2 monoclonal antibody (PPZ0506) was identified in 2017 [1]. Our previous study confirmed its cross-reactivity and specificity against rodent ESR2 proteins, enabling the elucidation of the true ESR2 distribution in rodents [2]. Objective: We aimed to determine the optimized conditions for immunohistochemical detection of rat ESR2 proteins using PPZ0506. <Method> Several staining conditions using paraffin-embedded and frozen ovary sections were evaluated, and the distribution of rat ESR2 proteins was analyzed under optimal conditions. Result: Immunohistochemical staining with PPZ0506 required appropriate antigen retrieval and antibody dilution. Subsequent immunohistochemical analysis in multiple tissues under optimized conditions revealed that rat ESR2 proteins are expressed in a more localized manner than previously assumed. Our optimized immunohistochemical detection of rat ESR2 proteins, using a well-validated antibody, revealed their distribution in limited tissues and cell types. Conclusion: Our results suggest that previous immunohistochemical studies using inadequately validated antibodies against ESR2 proteins overestimated their distribution profiles. We expect that our optimized immunohistochemistry using the PPZ0506 antibody may solve conflicting problems in ESR2 research. References: 1. Andersson S, et al. Nat Commun 15;8:15840 (2017) 2. Ishii H, et al. Int J Mol Sci 20(24):6312 (2019)