*Article* **E**ff**ect of Angiotensin II on Bone Erosion and Systemic Bone Loss in Mice with Tumor Necrosis Factor-Mediated Arthritis**

**Takahiko Akagi 1, Tomoyuki Mukai 1,\*, Takafumi Mito 1, Kyoko Kawahara 1, Shoko Tsuji 1, Shunichi Fujita 1, Haruhito A. Uchida <sup>2</sup> and Yoshitaka Morita <sup>1</sup>**


Received: 24 April 2020; Accepted: 7 June 2020; Published: 10 June 2020

**Abstract:** Angiotensin II (Ang II) is the main effector peptide of the renin-angiotensin system (RAS), which regulates the cardiovascular system. The RAS is reportedly also involved in bone metabolism. The upregulation of RAS components has been shown in arthritic synovial tissues, suggesting the potential involvement of Ang II in arthritis. Accordingly, in the present study, we investigated the role of Ang II in bone erosion and systemic bone loss in arthritis. Ang II was infused by osmotic pumps in tumor necrosis factor-transgenic (TNFtg) mice. Ang II infusion did not significantly affect the severity of clinical and histological inflammation, whereas bone erosion in the inflamed joints was significantly augmented. Ang II administration did not affect the bone mass of the tibia or vertebra. To suppress endogenous Ang II, Ang II type 1 receptor (AT1R)-deficient mice were crossed with TNFtg mice. Genetic deletion of AT1R did not significantly affect inflammation, bone erosion, or systemic bone loss. These results suggest that excessive systemic activation of the RAS can be a risk factor for progressive joint destruction. Our findings indicate an important implication for the pathogenesis of inflammatory bone destruction and for the clinical use of RAS inhibitors in patients with rheumatoid arthritis.

**Keywords:** angiotensin II; arthritis; bone erosion; inflammation; tumor necrosis factor; renin-angiotensin system; angiotensin II type 1 receptor
