Torpor-Induced Regulation of Poly(A) Tail Machinery in 13-Lined Ground Squirrel Brown Adipose Tissue

The poly(A) tail has long been known to play a central role in mRNA stability, storage, and translational competence, making it a potential key regulator during hypometabolic states. During seasonal torpor, hibernating mammals must frequently enter these hypometabolic states to survive. In this study, we examined protein abundance changes in key enzymes involved in poly(A) tail synthesis, binding, and removal during torpor in the brown adipose tissue of the 13-lined ground squirrel, Ictidomys tridecemlineatus, using immunoblots. BAT during late torpor exhibited significantly reduced abundance of the catalytic cleavage enzyme CPSF73, but increased abundance of poly(A) polymerase PAPOLA. In contrast, poly(A)-binding proteins and major complex subunits of deadenylases, including CCR4-Not, exhibited no significant changes. Furthermore, despite unchanged levels of the translation initiation factor eIF4E, the phosphorylated variant of 4E-BP1, a potent inhibitor of the initiation factor when hypophosphorylated, was significantly reduced during late torpor. Overall, constrained mRNA maturation, preserved transcript stability, and reversible translational inhibition suggest that an important role exists for poly(A) tail regulatory machinery in hypometabolic survival throughout the torpid state.