In pulmonary fibrosis lung tissue is thickened and scarred, and the lungs become progressively stiffer and smaller, leading to low levels of blood oxygen and shortness of breath. Lung fibrosis is not curable and life expectancy is reduced. Fibrosis is characterized by an increased accumulation of extracellular matrix (ECM) proteins such as collagen and elastin. ECM proteins are degraded predominantly by matrix metalloproteinases (MMPs). Here, we show that the lysosomal cation channel TRPML1, which causes the lysosomal storage disorder mucolipidosis type IV (MLIV) when mutated or lost, regulates the levels of MMPs in the ECM of mouse airways, modulating exocytosis of MMP2, 8, 9, 12, and 19, which mediate collagen/elastin degradation. While TRPML1 loss reduces MMP levels in lung macrophage and fibroblast supernatants, small molecule activation of TRPML1 results in increased levels. MLIV mice display a fibrosis-like lung phenotype similar to the phenotype evoked by bleomycin. We thus identify TRPML1 as a regulator of MMP release in the lung with loss of TRPML1 resulting in lung fibrosis due to excessive extracellular collagen and elastin accumulation.

The endolysosomal transient receptor potential mucolipin (TRPML) channels play key roles in regulating lysosomal trafficking, signaling, and function. While mutations in TRPML1 cause mucolipidosis type IV (MLIV), the functional consequences of many disease-associated mutations remain unclear. In this study, we used live-cell confocal imaging in HeLa cells to comprehensively characterize the subcellular localization and cation (Ca2+ and Zn2+) permeability of TRPML1-3, 10 TRPML1 MLIV patient-derived mutants, and engineered pore mutants. We showed that TRPML1 and TRPML3 permeate both Ca2+ and Zn2+, whereas TRPML2 conducts only Ca2+. Subcellular localization analyses revealed that TRPML1 and TRPML2 localize predominantly to lysosomes, whereas TRPML3 is preferentially localized to the endoplasmic reticulum. Among the 10 patient-derived TRPML1 mutants, nine exhibited severely impaired agonist-mediated Ca2+ and Zn2+ permeability, indicating severe functional loss. In contrast, the F408Δ mutant, associated with a milder phenotype, retained partial ion permeability and was the only mutant capable of constitutive Ca2+ permeation without agonist stimulation. Interestingly, we found that nonfunctional, lysosome-localized TRPML1 mutants are associated with more severe disease phenotypes than those retained in the endoplasmic reticulum, suggesting that lysosomal localization of nonfunctional TRPML1 may have dominant-negative or toxic effects. Finally, through structure-guided mutagenesis, we generated a metal-selective TRPML1 mutant, I468V, that is permeable to Ca2+ but not to Zn2+, providing a new tool for dissecting the distinct physiological roles of Zn2+ and Ca2+ in TRPML1-mediated processes. Together, these findings provide new insights into how TRPML1 mutations disrupt subcellular localization, ion permeability, and selectivity, which contribute to the variable clinical spectrum of MLIV.

Mucolipidosis type IV (MLIV) is classified as an exceptionally autosomal recessive condition due to a change in MCOLN1 that encodes the mucolipin-1 protein. ML-1 is a membrane protein comprising 6 Trans regions, which are situated at the LELs, a serine lipase area, and a nuclear localization sign. The characteristic features of the ML4 patients are mental retardation and skeletal deformities due to an increase in lipid molecules in the brain, other tissues, and organs. The fundamental goal of the work is to identify the most significant amino acid variants via a computational pipeline. The twenty-three amino acid variants that are responsible for the condition were retrieved from the public domain: L106P and L447P amino acid variants, with the following categories: extremely conserved, highly pathogenic, most interfering with protein function, more structurally unstable, and having promising Phenotyping characteristics was scrutinized from the series of bioinformatics tools that denote its significant nature. A docking and dynamics study was initiated to identify the interaction profiling and interatomic simulation between the Native, L106P, and L447P and the ligand ML-SA1 (it was known to ease the fatty acid buildup in lysosomes of cellular models of Mucolipidosis type IV) and had a score of -6.19, -5.12, and -5.21 kcal/mol, followed by a duplicate 100-ns run trajectory results, which assisted in detecting the stable nature of all the complex structures. Hence, this work helps to recognize the significant role of the scrutinized amino acid variants and, on the other hand, the stable nature of the ligand using standard computational tools.

Mucolipidosis IV (MLIV) is an autosomal-recessive pediatric disease that leads to motor and cognitive deficits and loss of vision. It is caused by loss of function of the lysosomal channel transient receptor potential mucolipin-1, TRPML1, and is associated with an early brain phenotype consisting of glial reactivity, hypomyelination, and lysosomal abnormalities. Although the field is approaching the first translationally relevant therapy, we currently lack a molecular signature of disease that can be used to detect therapeutic efficacy. Here, we analyzed 7,322 proteins in the plasma proteome from 17 MLIV patients and 37 controls and compared protein profiles with clinical measures of disease severity (motor function, muscle tone, and age). We found a decrease in neuronal proteins and an increase in muscle proteins in MLIV, consistent with neuronal dysfunction and muscle pathology observed in patients. Reduced synaptic proteins (e.g., GABARAP) best correlated with disease severity. Comparing the MLIV plasma proteome to the brain proteome from the MLIV mouse model identified shared alterations in 45 proteins, including upregulated proteins related to lysosomal function (e.g., ACTN2, GLB1) and downregulated proteins related to myelination (e.g., TPPP3, CNTN2). These data indicate that peripheral blood plasma protein signatures mirror changes found in the MLIV brain.

X-linked adrenoleukodystrophy (ALD) is a neurodegenerative disease primarily affecting male patients. Female patients with ALD are also affected in adulthood, yet their disease course and symptom burden remain poorly defined. In this single-site study, we set out to characterize disease burden in female individuals with ALD and identify barriers faced by this patient population. Adult female individuals with genetically or biochemically confirmed ALD were recruited through an outpatient specialty clinic and a patient advocacy group. We performed a retrospective chart review and conducted prospective telephone interviews to assess symptom presence and onset, interventions and management strategies, injuries, comorbidities, and quality of life (QOL). For comparison, we retrospectively gathered data from ALD diagnosis and symptom onset for adult male patients with ALD seen in our clinic. We included 127 female (median [interquartile range] age = 50.2 [39.2, 59.9]) and 82 male individuals with ALD (median [interquartile range] age = 37.5 [24.2, 43.9] years). Among our female cohort, 115 (91%) reported neurologic symptoms. The most common symptoms were urinary symptoms (74%), walking difficulty (66%), and spasticity (65%). Mental health symptoms were also common (64%). Of interest, 70 (55%) reported a history of falls, 61 (48%) had sustained injuries from falling, and 54 (43%) had a history of fractures. Compared with the male cohort, our female cohort had a significantly later age at symptom onset and diagnosis. In addition, symptom presentation was less likely to prompt a diagnosis in female individuals. Of 46 female individuals who sought clinical care for symptoms before diagnosis, 22 were initially misdiagnosed. Fifty-one (90%) of 57 female interviewees reported encountering challenges with health care access, and 49 (86%) reported a reduction in different aspects of QOL. Activities of daily living beyond walking were affected in 25 (44%) participants. We conclude that symptoms related to myelopathy and neuropathy are common in female individuals with ALD and that their disease burden is aggravated by the high rates of mental health problems, barriers to health care access, and injuries and complications requiring treatment. Limitations of our study include a risk for recall bias and selection bias.