Histochemical localization of palmitoyl protein thioesterase-activity

Infantile neuronal ceroid lipofuscinosis (INCL, Infantile Batten disease) is an invariably fatal neurodegenerative pediatric disorder caused by an inherited mutation in the PPT1 gene. Patients with INCL lack the lysosomal enzyme palmitoyl protein thioesterase-(PPT1, EC 3.1.2.22), resulting in intracellular accumulation of autofluorescent storage material and subsequent neuropathology. The Ppt1^-/- mouse is deficient in PPT1 activity and represents a useful animal model of INCL that recapitulates most of the clinical and pathological aspects of the disease. Preclinical therapeutic experiments performed in the INCL mouse include CNS-directed gene therapy and recombinant enzyme replacement therapy; both seek to re-establish therapeutic levels of the deficient enzyme. We present a novel method for the histochemical localization of PPT1 activity in the Ppt1^-/- mouse. By utilizing the substrate CUS-9235, tissues known to be positive for PPT1 activity turn varying intensities of blue. Presented here are histochemistry data showing the staining pattern in Ppt1^-/-, wild type, and Ppt1^-/- mice treated with enzyme replacement therapy or AAV2/9-PPT1-mediated gene therapy. Results are paired with quantitative biochemistry data that confirm the ability of CUS-9235 to detect and localize PPT1 activity. This new method complements the current tools for the study of INCL and evaluation of effective therapies.