Mas1, a receptor for angiotensin 1-7 (A1-7) derived from angiotensin II by angiotensin converting enzyme 2, is a key component of the counter-regulatory ACE2/Ang-(1-7)/Mas1 axis of the renin-angiotensin system. It plays a crucial role in various biological processes, such as regulating vascular tone by inducing vasodilation and attenuating Ang II-induced vasoconstriction [1]. It is also involved in reproductive processes like folliculogenesis, steroidogenesis, oocyte maturation, and ovulation, and its changes may contribute to ovarian pathological conditions [2].

In breast cancer, MAS1 expression was found to be attenuated in invasive ductal carcinoma, especially scirrhous IDC. In triple-negative breast cancer cell lines expressing MAS1, activation with A1-7 suppressed cell growth, anti-apoptotic survival, and invasion, while knockdown enhanced these processes. Additionally, combination treatments showed synergic effects on tumor growth inhibition, suggesting MAS1 as a possible molecular target for breast cancer [3].

In endometriosis, MAS1 mRNA levels were increased in ovarian endometriotic tissues and eutopic proliferative endometria of patients, indicating its potential role in promoting the initiation of endometriosis via migration of proliferative tissue [4]. Also, in pain regulation, intrathecal injection of Ang (1-7) attenuated the nociceptive response induced by substance P and NMDA via spinal MAS1, which co-localized with NK1 and NMDA receptors, suggesting it as a therapeutic target for spinal pain transmission [5].

In conclusion, Mas1 is an important receptor involved in the renin-angiotensin system, playing diverse roles in vascular regulation, reproductive function, and disease processes such as breast cancer, endometriosis, and pain regulation. Functional studies in these areas, although not specifically from KO/CKO mouse models in the provided references, have revealed its potential as a therapeutic target in related diseases.