Abstract 672: A genetic defect in phenylalanine hydroxylase (PAH) affects the immune system in kidney

Abstract

Abstract PAH, one of the genes associated with inborn error of metabolism (IEM), codes for phenylalanine hydroxylase and is specifically expressed in the liver and kidney. When PAH is dysfunctional, phenylalanine (Phe) cannot be converted to tyrosine (Tyr), and it produces toxic metabolites such as phenylpyruvate by a metabolic shift. We previously analyzed germline variants of IEM-related genes using public cancer multi-omics data. As a result, there was a high frequency of mutations in the PAH gene, and germline variants were particularly high in renal cell carcinoma (RCC). Based on this data, we suggest that kidney-specific expressed PAH mutations could change the kidney tissue microenvironment, which makes them more vulnerable to chronic kidney disease (CKD) and affects cancer development. We used the PAH enu2 mice model, which has a missense mutation in the PAH gene. PAH homozygous mutant mice display phenylketonuria (PKU) when not maintained on a Phe-free diet. PAH enu2 mice were maintained a normal diet. The concentration of phenylalanine in the mice's serum was measured each week. Then, the proportions of immune cells were analyzed in peripheral blood and kidney. Next, Jurkat cells, which are well-known as human T-cell lines, were applied to the in vitro experiment. Jurkat cells were cultured in a medium containing Phe or PPA and were activated by PHA/PMA or anti-CD3/CD28. Then after, the expression of immune-related markers was evaluated. Additionally, the expression of the PAH enzyme in human RCC and normal tissue was assessed by immunohistochemistry (IHC). The concentration of Phe in mice serum was higher when the PAH gene was defective; homozygous mutant, heterozygous mutant. As PAH-defective mice got older, the T cell population decreased in the blood and kidney immune cells. When Jurkat T cells were cultured with Phe or PPA, the expression of IL-2, a cytokine related to T cell expansion, decreased in the PPA-treated and activated group. There were more significant changes when treated with PPA rather than Phe. IHC data shows the expression of PAH was significantly decreased in RCC tissues compared to non-tumor tissue. These results suggest that the immune system could be changed by PAH dysfunction bearing a germline mutation. Moreover, the kidney tissue microenvironment with PAH defects is vulnerable to the development of kidney disease, which can lead to RCC. This is a novel discovery that can explain the importance of the role PAH gene in kidney disease. Citation Format: Seojeong Kim, Chaelin Kang, Jihyun Park, Seung Seok Han, Youngil Koh, Sung-Soo Yoon. A genetic defect in phenylalanine hydroxylase (PAH) affects the immune system in kidney [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 672.