TPP1 and frontotemporal dementia: First, we treated HDF cells from two separate GRN-FTD patients (i.e., PGRN haploinsufficient cells) with 50 μM A41 for 72 h and measured the levels of cleaved (i.e., lysosomal) TPP1, a protein significantly decreased in both LysoIP and whole-cell lysate TMT-MS datasets.