1. New chemical tools for studying endolysosomal two-pore channels
- Author
-
Yuan, Yu
- Subjects
571.6 - Abstract
Two-pore channels (TPCs) are endolysosomal ion channels of physiological and pathophysiological significance. However, fundamental properties concerning ion permeability and activation mechanisms are ambiguous. Also, as the likely targets for Ca2+-mobilizing messenger NAADP, the role of TPCs in cell-wide Ca2+ signalling is ill-defined. Importantly, their pharmacology is limited to cell-impermeable activators and a few non-selective inhibitors, which brings challenges for characterizing TPCs. In this thesis, I address the above issues. I began by examining the mechanism of action of the lysosomotropic agent, glycyl-L- phenylalanine 2-naphthylamide (GPN), which has long been appreciated for mediating Ca2+ signals from lysosomes and for probing TPC function. Its action on lysosomes has recently been questioned. However, using fibroblasts, here I show that GPN mobilises Ca2+ from acidic organelles. I move on to characterise two cell-permeable and selective TPC2 activators (A1 and H07). Additionally, I confirm that approved drugs targeting estrogen and dopamine receptors are selective TPC2 inhibitors. I go on to show that A1 and H07 activate TPC2 differentially. A1 induced larger and quicker Ca2+ signals than H07 but similar Na+ signals. A1 and H07 targeted distinct sites on TPC2. Besides, H07 but not A1-induced Ca2+ signals were regulated by external (luminal) pH. The implication is that TPC2 may be regulated in an agonist- specific manner. Finally, by using GPN and inhibiting TPC activity with novel inhibitors or siRNA knockdown, I show that TPCs are required for histamine- but not bradykinin-induced Ca2+ signals. More specifically, histamine-mediated Ca2+ signals were reduced upon TPC2 but not TPC1 knockdown. Thus, TPCs are implicated in global Ca2+ signalling evoked by physiological stimuli likely in an isoform-dependent manner. Collectively, this research has provided novel TPC modulators with which to further characterize fundamental properties and physiological roles of TPCs.
- Published
- 2021