ZnT2 accumulates zinc in lysosomes and mitochondria to signal mammary gland involution

Abstract

Post‐lactation, the mammary gland (MG) undergoes massive apoptotic‐ and lysosomal‐mediated cell death and involutes back to the pre‐pregnant state. Recent data from our lab suggests zinc (Zn) import into specific intracellular compartments regulates this process. We found that the Zn transporter ZnT2 imports Zn into vesicles, which is required for Zn transfer into milk during lactation. In addition, ZnT2 imports Zn into mitochondria, which decreases ATP and activates apoptosis in mammary epithelial cells (MECs). Thus, we hypothesized that ZnT2‐mediated Zn accumulation into lysosomes and mitochondria signals MG involution (INVO). We determined that ZnT2 accumulates in lysosomes using sucrose gradient fractionation of MG from involuting mice. This increased lysosomal Zn and activity of the Zn‐dependent lysosomal enzyme acid phosphatase (AP), a marker of INVO. ZnT2 overexpressed in MECs in vitro co‐localized with lysosomes (LAMP1) and mitochondria (Mitotracker) and increased AP activity, apoptosis and cell death. ZnT2 overexpressed in MG using a recombinant adenovirus in vivo increased mitochondrial Zn, activated apoptosis and increased AP activity, which activated premature INVO. Collectively, these data suggest Zn accumulation into lysosomes and mitochondria acts as a regulatory signal to induce MG INVO. Dysregulation in this process may lead to premature INVO and suboptimal lactation.Grant Funding Source: Supported by NIH R01 HD058614 to SLK