Rap1a, also known as Ras-associated protein 1A, is a small GTP-binding protein belonging to the Ras subfamily. It is involved in multiple cellular processes such as cell adhesion, migration, and signal transduction, with key associated pathways including the ERK, Akt, and mTORC1 signaling pathways. Its regulation is crucial for normal cellular functions, and understanding its function can be significantly enhanced through genetic models like gene knockout (KO) and conditional knockout (CKO) mouse models [1-8].

In various disease-related studies, KO/CKO mouse models have revealed Rap1a's role. In orthodontic treatment, compression-induced upregulation of CD97 inhibits osteoclast differentiation via the Rap1a/ERK pathway; inhibiting Rap1a can accelerate tooth movement [1]. In the context of obesity-and statin-associated hyperglycemia, hepatocyte Rap1a activation suppresses gluconeogenic gene expression and glucose production. Obesity and statins suppress Rap1a activation, leading to hyperglycemia, and restoring its activity improves glucose intolerance [2]. In hepatic steatosis, activation of hepatic Rap1a is suppressed in obese mice with metabolic dysfunction-associated steatotic liver disease (MASLD). Restoring its activity decreases liver steatosis by inhibiting mTORC1-mediated SREBP1 cleavage [3]. In the lung endothelium, EC-specific Rap1a knockout mice display an inflammatory lung phenotype, as Rap1a normally modulates Orai1-mediated calcium entry, which is crucial for NFAT-mediated transcription and endothelial inflammation [4]. In esophageal squamous cell carcinoma, Rap1a promotes metastasis through the AKT signaling pathway [5]. In acute graft-versus-host disease (aGVHD) after umbilical cord blood transplantation, RAP1A expression is elevated in patients, negatively correlating with Treg cells [6].

In summary, Rap1a is essential for multiple biological processes, and its dysregulation is associated with various diseases including orthodontic-related bone remodeling issues, metabolic disorders, liver diseases, vascular inflammation, cancer metastasis, and aGVHD. Studies using KO/CKO mouse models have provided valuable insights into its role in these disease conditions, which may help in developing targeted therapeutic strategies.

References:

1. Wang, Wen, Wang, Qian, Sun, Shiying, Ma, Zhe, Lu, Haiyan. 2024. CD97 inhibits osteoclast differentiation via Rap1a/ERK pathway under compression. In International journal of oral science, 16, 12. doi:10.1038/s41368-023-00272-x. https://pubmed.ncbi.nlm.nih.gov/38311610/

2. Wang, Yating, Spolitu, Stefano, Zadroga, John A, Sarecha, Amesh K, Ozcan, Lale. . Hepatocyte Rap1a contributes to obesity- and statin-associated hyperglycemia. In Cell reports, 40, 111259. doi:10.1016/j.celrep.2022.111259. https://pubmed.ncbi.nlm.nih.gov/36001955/

3. Agarwal, Heena, Wang, Yating, Tinsley, Brea, Wang, Xiaobo, Ozcan, Lale. 2024. RAP1A suppresses hepatic steatosis by regulating amino acid-mediated mTORC1 activation. In JHEP reports : innovation in hepatology, 7, 101303. doi:10.1016/j.jhepr.2024.101303. https://pubmed.ncbi.nlm.nih.gov/40124164/

4. Kosuru, Ramoji, Romito, Olivier, Sharma, Guru Prasad, Trebak, Mohamed, Chrzanowska, Magdalena. 2024. Rap1A Modulates Store-Operated Calcium Entry in the Lung Endothelium: A Novel Mechanism Controlling NFAT-Mediated Vascular Inflammation and Permeability. In Arteriosclerosis, thrombosis, and vascular biology, 44, 2271-2287. doi:10.1161/ATVBAHA.124.321458. https://pubmed.ncbi.nlm.nih.gov/39324266/

5. Li, Qinfang, Xu, Aiping, Chu, Yuan, Zhou, Pinghong, Xu, Meidong. 2019. Rap1A promotes esophageal squamous cell carcinoma metastasis through the AKT signaling pathway. In Oncology reports, 42, 1815-1824. doi:10.3892/or.2019.7309. https://pubmed.ncbi.nlm.nih.gov/31545475/

6. Wang, Shaochen, Wang, Dongyao, Chang, Yuting, Zhou, Ziwei, Liu, Huilan. 2022. Elevated RAP1A expression correlates with the severity of acute GVHD after umbilical cord blood transplantation. In Transplant immunology, 71, 101546. doi:10.1016/j.trim.2022.101546. https://pubmed.ncbi.nlm.nih.gov/35114361/