The angiotensin converting enzyme 2/angiotensin-(1-7)/Mas Receptor axis as a key player in alveolar bone remodeling

The renin-angiotensin system (RAS), aside its classical hormonal properties, has been implicated in the pathogenesis of inflammatory disorders. The angiotensin converting enzyme 2/angiotensin-(1-7)/Mas Receptor (ACE2/Ang-(1-7)/MasR) axis owns anti-inflammatory properties and was recently associated with bone remodeling in osteoporosis. Thus, the aim of this study was to characterize the presence and effects of the ACE2/Ang-(1-7)/MasR axis in osteoblasts and osteoclasts in vitro and in vivo. ACE2 and MasR were detected by qPCR and western blotting in primary osteoblast and osteoclast cell cultures. Cells were incubated with different concentrations of Ang-(1-7), diminazene aceturate (DIZE - an ACE2 activator), A-779 (MasR antagonist) and/or LPS in order to evaluate osteoblast alkaline phosphatase and mineralized matrix, osteoclast differentiation and cytokine expression, and mRNA levels of osteoblasts and osteoclasts markers. An experimental model of alveolar bone resorption triggered by dysbiosis in rats was used to evaluate bone remodeling in vivo. Rats were treated with Ang-(1-7), DIZE and/or A-779 and periodontal samples were collected for immunohistochemistry, morphometric analysis, osteoblast and osteoclast count and cytokine evaluation. Human gingival samples from healthy and periodontitis patients were also evaluated for detection of ACE2 and MasR expression. Osteoblasts and osteoclasts expressed ACE2 and MasR in vitro and in vivo. LPS stimulation or alveolar bone loss induction reduced ACE2 expression. Treatment of bone cells with Ang-(1-7) or DIZE stimulated osteoblast ALP, matrix synthesis, upregulated osterix, osteocalcin and collagen type 1 transcription, reduced IL-6 expression, and decreased osteoclast differentiation, RANK and IL-1β mRNA transcripts, and IL-6 and IL-1β levels, in a MasR-dependent manner. In vivo, Ang-(1-7) and DIZE decreased alveolar bone loss through improvement of osteoblast/osteoclast ratio. A-779 reversed such phenotype. ACE2/Ang-(1-7)/MasR axis activation reduced IL-6 expression, but not IL-1β. ACE2 and MasR were also detected in human gingival samples, with higher expression in the healthy than in the inflamed tissues. These findings show that the ACE2/Ang-(1-7)/MasR is an active player in alveolar bone remodeling.