A new study published in the BMB Reports indicates that stress hormones such as epinephrine (adrenaline) may promote the transformation of M1-type macrophages to M2-type macrophages and, thus, accelerate tumor growth in a mouse model of breast cancer.
Several studies have linked psychological stress and breast cancer risk, associating with the involvement of stress mediators such as epinephrine (adrenaline) and norepinephrine (noradrenaline), and their effects on α- and β-adrenergic receptors.
Both α- and β- adrenoceptors appear to influence breast cancer progression through increasing breast cancer cell proliferation or affecting angiogenesis and the inflammatory response in the tumor microenvironment (EI Obeid & Conzen SD, 2013; KS Madden et al., 2011).
On the other hand, macrophages are also associated with cancer, being classified in two types: M1 and M2. M1-type macrophages inhibit cancer development, while M2-type stimulate cancer growth and proliferation.
In human breast carcinomas, tumor-associated macrophages (TAM) are also reported and their density correlates with poor prognosis (D Laoui et al., 2011). Also, it appears that in breast cancer, tumor cells are able to attract M2 macrophages that further promote invasion and suppress adaptive immunity, promoting tumor growth (RA Mukhtar et al., 2011).
In an attempt to assess the role of psychological stress and M2 macrophages in the development of breast cancer, Jun-Fang Qin and colleagues, from the School of Medicine, Nankai University, China, inoculated breast cancer cell lines 4T1 in mice followed by 3 weeks of social isolation stress, and analyzed the cellular development of the tumor and macrophage differentiation.
The authors found that stressed animals had increased levels of epinephrine, enhanced growth of the breast tumors and greater differentiation of intratumoral M2-type macrophages. In vitro experiments showed that epinephrine induced the transformation from M1-type to M2-type macrophage phenotype. The non-selective β-adrenoceptor antagonist and blocker propranolol reduced the number of M2 macrophages, indicating the involvement of β-adrenoceptors in this process.
The authors also detected β2-adrenoceptors and the human M2 macrophages marker CD163 in tissues obtained from breast cancer patients, and importantly, in this case, β2-adrenoceptors and the CD163 marker were co-expressed on carcinoma cells.