Figure 2.

Effect of TPC2-A1-P on cholesterol accumulation in selected patient fibroblasts (HF) and electrophysiological characterization of a novel patient mutation (MCOLN1^T121M/T121M). (A) Effect of TPC2-A1-P or the TRPML1 activators ML-SA1 and MK6-83 on cholesterol accumulation in WT, MLIV and selected patient fibroblasts, carrying MLIV-causing point mutations as indicated, visualized by filipin. MCOLN1^T121M/T121M is a severely mislocalized variant (B) found to be homozygously expressed in a patient from a Yazidi family, recently diagnosed with MLIV (Prof. Thorsten Marquardt, University of Münster, Münster, Germany). The patient, an 18-year-old woman, showed a comparably mild clinical phenotype for her age (ability to walk and talk, delayed development with retinal degeneration (risk of blindness), reduced iron (39 µg/dL (60–140)) and ferritin (6 µg/L (16–92)) levels, reduced Hb, HCT, MCV and MCHC (iron deficiency anemia), slightly deranged liver function (ASAT: 56 U/L (<30) and ALAT: 42 U/L (<30))). Electrophysiology revealed TRPML1^T121M/T121M to retain some residual channel activity. (C–F) Shown are representative currents (I-V traces) from vacuolin-enlarged LE/LY, isolated from WT or patient fibroblasts (HF), activated by ML-SA1 or ML1-SA1 (=EVP169 = selective TRPML1 agonist). * p-value < 0.05; *** p-value < 0.001; **** p-value < 0.0001.