Endocytic Trafficking and Human Diseases

National Heart, Lung, And Blood Institute

Investigators

Linked publications & trials

Abstract

Mucolipidosis type IV (MLIV) is an autosomal recessive disorder characterized by acute psychomotor delays, achlorydria, and visual abnormalities including retinal degeneration, corneal clouding, optic atrophy, and strabismus. Lysosomal inclusions are found in most tissues in MLIV patients. The composition of the storage material is heterogeneous and includes lipids and mucopolysaccharides forming characteristic multiconcentric lamellae, as well as soluble, granulated proteins. MLIV is caused by mutations in mucolipin-1 (MCOLN1, also known as TRPML1), an endo-lysosomal cation channel belonging to the transient receptor potential (TRP) superfamily of ion channels. Whole cell patch clamp, as well as recording of native endolysosomal membranes, suggest that MCOLN1 functions as an inwardly (from lumen to cytoplasm) rectifying channel permeable to Ca2+, Na+, K+ and Fe2+/ Mn2+ whose activity is potentiated by low pH. To better understand the pathology of this disease, we used genome editing to knockout the two mcoln1 genes present in Dario rerio (zebrafish). Our model successfully reproduced the retinal and neuromuscular defects observed in MLIV patients, indicating that this model is suitable for studying the disease pathogenesis. Importantly, our model revealed novel insights into the origins and progression of the MLIV pathology, including the contribution of autophagosome accumulation to muscle dystrophy and the role of mcoln1 in embryonic development, hair cell viability and cellular maintenance. The generation of a MLIV model in zebrafish is particularly relevant given the suitability of this organism for large-scale in vivo drug screening, thus providing novel opportunities for therapeutic discovery. Pompe disease, a severe muscle wasting disorder characterized by altered lysosomal function. Profound muscle atrophy is a hallmark of Pompe disease, a rare genetic disorder caused by a deficiency of acid alphaglucosidase (GAA), the enzyme that breaks down glycogen to glucose within lysosomes. Absence of the enzyme leads to a rapidly fatal cardiomyopathy and skeletal muscle myopathy in infants; low levels of residual enzyme activity are associated with childhood and adultonset progressive skeletal muscle myopathy usually without cardiac involvement. Recently, we found dysregulation of mTOR signaling in the diseased muscle cells, and focused on the identification of potential sites for therapeutic intervention. Importantly, reactivation of mTOR in the whole muscle of Pompe mice by TSC knockdown resulted in the reversal of atrophy and a striking removal of autophagic buildup. Of particular interest, we found that the aberrant mTOR signaling can be reversed by arginine. This finding can be translated into the clinic and may become a paradigm for targeted therapy in lysosomal, metabolic, and neuromuscular diseases.