Uncovering the Unique Roles of Cathepsins B and L in Purkinje Cells Using Nervous System-Specific CTSB and CTSL Double-Deficient Mice.

Defects in the autophagy-lysosomal degradation pathway contribute to neurodegenerative diseases. Cathepsins B (CtsB) and L (CtsL) are major lysosomal cysteine proteases. Mice deficient in both CtsB and CtsL exhibit abnormalities not only in neural tissue but in other organs, such as heart and liver, with most dying at approximately 16 days of age. To investigate the roles of CtsB and CtsL in the nervous system, nervous system-specific CTSB and CTSL double-knockout mice (CtsB/L-NES: CTSBflox/flox; CTSLflox/flox; Nestin-Cre) were generated. These mice displayed tail elevation, motor dysfunction, and hyperactivity. In adulthood, they developed cerebellar atrophy, with Purkinje cells in the cerebellar cortex showing selective loss of phospholipase C β4-positive and Zebrin II-negative Purkinje cells in a striped pattern. Ubiquitin-positive structures accumulated in the perikarya and axons of Purkinje cells, reflecting impaired autophagy-lysosomal degradation. Activation of astrocytes and microglia was observed in Purkinje cell loss regions. Electron microscopy revealed granular osmiophilic deposit-like structures in perikarya, autophagosome-like accumulations in axons, and a reduction in synaptic vesicles at active regions of swollen axon terminals in Purkinje cells. Additionally, neuronal loss was observed specifically in the ventral posterior lateral and ventral posterior medial nuclei of the thalamus. These findings demonstrate CtsB and CtsL are essential for survival of Purkinje cells in the cerebellum and neurons in the ventral posterior lateral and ventral posterior medial nuclei of the thalamus.