LAMP2 MUTANT <EM>XENOPUS TROPICALIS</EM> SHOW HALLMARKS OF SYNAPSE-SPECIFIC ALTERATIONS

LAMP2 is a lysosomal membrane protein that plays a key role in endolysosomal function and autophagy. In humans, loss of function mutations in LAMP2 cause Danon disease (DD), a rare lysosomal storage disorder associated with myopathies, retinal dysfunction and intellectual disability. Four LAMP2 truncated mutant lines were successfully generated by CRISPR/Cas 9 edition using sgRNAs targeting exon 3. F0s and heterozygous F1 and F2 animals developed normally. Histological analysis of homozygous F2 mutant tadpoles confirmed the absence of functional LAMP2 expression. LAMP2 (-/-) tadpoles showed alterations in mitochondria and the endoplasmic reticulum of muscle tissue which disrupted normal swimming. Mitochondria present in the inner segment of photoreceptors appeared selectively damaged in rods, causing a vision impairment. We investigated alterations in synapses established in the retina and the olfactory bulb by photoreceptors and olfactory sensory neurons, respectively. Autophagic structures and endolysosomal compartments were rarely present in WT photoreceptor ribbon synapses but increased in LAMP2 (-/-) tadpoles. Although autophagic intermediates were commonly distributed in axon terminals of olfactory sensory neurons, they significantly increased in LAMP2 (-/-) tadpoles. Live imaging of acidic organelles showed an overall enhancement of their mobility in olfactory sensory neurons, indicating alterations in lysosome trafficking or function. The data obtained show that LAMP2 mutant X. tropicalis reproduce relevant hallmarks of DD. The accumulation of autophagosomes and alterations in mitophagy present in retinal and olfactory bulb synapses suggest the presence of a synaptopathy and, therefore, a widespread alteration in the processing of sensory information in this disease.