Mechanisms of activation of lysosomal two-pore channel TPC2, a potential novel target for the treatment of lysosomal storage disorders and neurodegenerative diseases

• Applicant: Professor Dr. Christian Michael Grimm
• Subject Area: Pharmacology ; Biophysics
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 440563025

• Final Report Year: 2023

Final Report Abstract

Three major research objectives had been defined for this proposal: Objective 1: Define the ion selectivity of endolysosomal two-pore cation channel TPC2 in response to TPC2 agonists. Objective 2: Identify agonist binding sites on TPC2. Objective 3: Apply the agonists to define physiological and pathophysiological roles for TPC2 and to establish TPC2 as drug target. We have successfully addressed all three objectives of this proposal. We assessed the ion selectivity profile in response to TPC2 agonists, alone and in combination, i.e. effects of the endogenous activators PI(3,5)P2 and NAADP, and the combination of both, and on the other hand we examined effects of the lipophilic small molecule agonists TPC2-A1-P and TPC2-A1-N, mimicking the PI(3,5)P2 and NAADP effects, respectively, alone and in combination. Specifically, it was found that the newly identified agonists result either in increased Na+ but only little Ca2+ permeability (TPC2-A1-P) or an increased Ca2+-permeable state (TPC2-A1-N) (Objective 1). The two compounds were named TPC2-A1-P and TPC2-A1-N to reflect their functional similarity to PI(3,5)P2 and NAADP as the former ones essentially mimic the effects of the latter ones despite being structurally different. Furthermore, for TPC2-A1-P it was demonstrated that the K204A mutation in TPC2 (the mutation is located within the PI(3,5)P2 binding pocket) abrogates TPC2-A1-P activity, while leaving TPC2-A1-N activity unaffected (Objective 2). A potential binding site for TPC2-A1-N has in the meantime also been discovered. Surprisingly, co-application of the two agonists evoked a markedly potentiated Ca2+ response compared to TPC2-A1-N or TPC2-A1-P alone. Wang and Zhu corroborated these data recently and concluded that TPCs exhibit different modes of activation when stimulated by NAADP or PI(3,5)P2, respectively. Further, they showed that co-application of NAADP and PI(3,5)P2 synergistically activates TPC2 and proposed that PI(3,5)P2 may be required for NAADP signaling, essentially confirming our results. These results have important implications for drug discovery and TPC2 as a drug target. In a further study we could apply TPC2-A1-P successfully to rescue neurodegenerative lysosomal storage phenotypes in mucolipidosis type IV, Niemann Pick disease type C1 and Batten disease in patient fibroblasts, iPSC derived cortical neurons and in vivo in a mouse model of mucolipidosis type IV (Objective 3). Whether TPC2-A1-N/NAADP has similar rescue capabilities will be addressed in a separate study. The published results and presentation of the results at international conferences have fostered industry collaborations with whom we will follow up on this project to develop it further and to potentially bring novel molecules to the patient for neurodegenerative disease therapy.

Publications

• Agonist-mediated switching of ion selectivity in TPC2 differentially promotes lysosomal function. eLife, 9.
  Gerndt, Susanne; Chen, Cheng-Chang; Chao, Yu-Kai; Yuan, Yu; Burgstaller, Sandra; Scotto, Rosato Anna; Krogsaeter, Einar; Urban, Nicole; Jacob, Katharina; Nguyen, Ong Nam Phuong; Miller, Meghan T.; Keller, Marco; Vollmar, Angelika M.; Gudermann, Thomas; Zierler, Susanna; Schredelseker, Johann; Schaefer, Michael; Biel, Martin; Malli, Roland ... & Grimm, Christian
  
• Neurodegenerative Lysosomal Storage Disorders: TPC2 Comes to the Rescue!. Cells, 11(18), 2807.
  Prat, Castro Sandra; Kudrina, Veronika; Jaślan, Dawid; Böck, Julia; Scotto, Rosato Anna & Grimm, Christian
  
• Segregated cation flux by TPC2 biases Ca2+ signaling through lysosomes. Nature Communications, 13(1).
  Yuan, Yu; Jaślan, Dawid; Rahman, Taufiq; Bolsover, Stephen R.; Arige, Vikas; Wagner, Larry E.; Abrahamian, Carla; Tang, Rachel; Keller, Marco; Hartmann, Jonas; Rosato, Anna S.; Weiden, Eva-Maria; Bracher, Franz; Yule, David I.; Grimm, Christian & Patel, Sandip
  
• TPC2 rescues lysosomal storage in mucolipidosis type IV , Niemann–Pick type C1, and Batten disease. EMBO Molecular Medicine, 14(9).
  Scotto, Rosato Anna; Krogsaeter, Einar K.; Jaślan, Dawid; Abrahamian, Carla; Montefusco, Sandro; Soldati, Chiara; Spix, Barbara; Pizzo, Maria Teresa; Grieco, Giuseppina; Böck, Julia; Wyatt, Amanda; Wünkhaus, Daniela; Passon, Marcel; Stieglitz, Marc; Keller, Marco; Hermey, Guido; Markmann, Sandra; Gruber‐Schoffnegger, Doris; Cotman, Susan ... & Grimm, Christian
  
• TRPMLs and TPCs: Targets for lysosomal storage and neurodegenerative disease therapy?. Cell Calcium, 103, 102553.
  Krogsaeter, Einar; Rosato, Anna Scotto & Grimm, Christian
  
• PI(3,5)P2 and NAADP: Team players or lone warriors? – New insights into TPC activation modes. Cell Calcium, 109, 102675.
  Jaślan, Dawid; Ferro, Irene Flavia; Kudrina, Veronika; Yuan, Yu; Patel, Sandip & Grimm, Christian