Fig. 1

A Classical androgen receptor (AR) signaling pathway. When unbound, AR is localized in the cytoplasm associated with molecular chaperones. Binding of AR to its appropriate ligand induces a conformational change that leads to the dissociation of AR from the protein chaperones. AR then interacts with co-regulators that facilitate nuclear targeting and dimerization. AR typically forms a homodimer and is then translocated across the nuclear membrane where it binds to androgen response elements (AREs) and induces the transcription of  androgen-dependent genes [9, 10]. B Sex hormone binding globulin (SHBG) binds androgens and estrogens and transports these steroids in the systemic circulation. SHBG is believed to also be involved in steroid hormone signaling [11]. C 3α-Androstanediol has been shown to interact with the γ-aminobutyric acid (GABA)-A receptor and increase GABA receptor (GBR) function, mediating the GABA-A chloride ion flux demonstrated in Long Evans rats [8]. GABA-A receptor activation has been shown to inhibit retinal regeneration in damaged retina in zebrafish [12]. Pie charts adjacent to proteins represent the protein’s relative abundance in the periphery (blue), macula (orange), and fovea (gray) based on the mass spectrometry data provided by the Skeie and Mahajan [5] study