SAA1, Serum Amyloid A1, is a lipid-binding protein and an acute-phase reactant. It is synthesized mainly in the liver and is part of the acute-phase response, contributing to high-density lipoproteins and cholesterol transport. SAA1 has been implicated in multiple biological processes, including tissue remodeling, inflammation, and host defense. It interacts with specific receptors and is involved in pathways like NF-κB/p38/JNK, TGFβ/Smad, and S1P/S1PR1-β-catenin, playing important roles in various diseases [3,4,5,6].

In pancreatic cancer, co-culturing adipocytes with pancreatic cancer cells led to the formation of cancer-associated adipocytes (CAAs). CAAs promoted pancreatic cancer cell migration, invasion, chemoresistance, and epithelial-mesenchymal transition (EMT) via SAA1 expression. Knocking down SAA1 in PANC-1 cells attenuated these malignant characteristics, suggesting SAA1 as a novel therapeutic target [1]. In triple-negative breast cancer (TNBC), SAA1 was identified as a regulator of adipocyte reprogramming. Its expression was associated with cancer-associated adipocyte infiltration, inflammation, and stem-like properties of TNBC [2]. In esophageal squamous cell carcinoma (ESCC), SAA1 promoted cell proliferation, migration, and tumor growth in nude mice, and the S1P/S1PR1 pathway regulated SAA1 expression to activate β-catenin [6]. In renal cancer, high SAA1 expression was found in advanced clear cell renal cell carcinoma (ccRCC), and it could potentially serve as a diagnostic and prognostic biomarker [7]. In a mouse model of cardiac remodeling induced by transverse aortic banding, SAA1-deficient mice showed less cardiac fibrosis, indicating that SAA1 absence hindered cardiac fibrosis through inhibiting NF-κB/p38/JNK and TGFβ/Smad pathways [5]. In non-alcoholic fatty liver disease (NAFLD), knockout or knockdown of SAA1/2 in mice alleviated hepatic steatosis and inflammation, while overexpression of SAA1 aggravated these conditions via the TLR4-mediated NF-κB signaling pathway [8].

In conclusion, SAA1 plays diverse and significant roles in multiple disease conditions, including cancer, cardiac remodeling, and NAFLD. Gene knockout and knockdown models have been crucial in revealing its functions in promoting tumor progression, regulating adipocyte reprogramming, influencing cardiac fibrosis, and exacerbating hepatic steatosis. These findings suggest SAA1 as a potential therapeutic target in related diseases.

References:

1. Takehara, Masanori, Sato, Yasushi, Kimura, Tetsuo, Muguruma, Naoki, Takayama, Tetsuji. 2020. Cancer-associated adipocytes promote pancreatic cancer progression through SAA1 expression. In Cancer science, 111, 2883-2894. doi:10.1111/cas.14527. https://pubmed.ncbi.nlm.nih.gov/32535957/

2. Rybinska, Ilona, Mangano, Nunzia, Romero-Cordoba, Sandra L, Tagliabue, Elda, Triulzi, Tiziana. 2024. SAA1-dependent reprogramming of adipocytes by tumor cells is associated with triple negative breast cancer aggressiveness. In International journal of cancer, 154, 1842-1856. doi:10.1002/ijc.34859. https://pubmed.ncbi.nlm.nih.gov/38289016/

3. Papa, Riccardo, Lachmann, Helen J. 2018. Secondary, AA, Amyloidosis. In Rheumatic diseases clinics of North America, 44, 585-603. doi:10.1016/j.rdc.2018.06.004. https://pubmed.ncbi.nlm.nih.gov/30274625/

4. Sack, George H. . Serum Amyloid A (SAA) Proteins. In Sub-cellular biochemistry, 94, 421-436. doi:10.1007/978-3-030-41769-7_17. https://pubmed.ncbi.nlm.nih.gov/32189310/

5. Xiao, Yusha, Ni, Lihua, Shi, Hongjie, Liu, Jinping, Luo, Pengcheng. . SAA1 deficiency alleviates cardiac remodeling by inhibiting NF-κB/p38/JNK and TGFβ/Smad pathways. In FASEB journal : official publication of the Federation of American Societies for Experimental Biology, 37, e22911. doi:10.1096/fj.202201506R. https://pubmed.ncbi.nlm.nih.gov/37022639/

6. Li, Qianqian, Tang, Maolin, Zhao, Shisheng, Ren, Ling, Hu, Weimin. 2024. SAA1 regulated by S1P/S1PR1 promotes the progression of ESCC via β-catenin activation. In Discover oncology, 15, 66. doi:10.1007/s12672-024-00923-3. https://pubmed.ncbi.nlm.nih.gov/38446289/

7. Li, Sen, Cheng, Yongbiao, Cheng, Gong, Ruan, Hailong, Zhang, Xiaoping. 2021. High SAA1 Expression Predicts Advanced Tumors in Renal Cancer. In Frontiers in oncology, 11, 649761. doi:10.3389/fonc.2021.649761. https://pubmed.ncbi.nlm.nih.gov/34084746/

8. Jiang, Bin, Wang, Dongdong, Hu, Yunfu, Ben, Jingjing, Chen, Qi. 2022. Serum amyloid A1 exacerbates hepatic steatosis via TLR4-mediated NF-κB signaling pathway. In Molecular metabolism, 59, 101462. doi:10.1016/j.molmet.2022.101462. https://pubmed.ncbi.nlm.nih.gov/35247611/