Mucolipidosis Type Research Articles

Révélation néonatale d’une mucolipidose de type II

Mucolipidosis type II (ML II, OMIM 252,500) is an autosomal recessive disorder clinically characterized by facial dysmorphia similar to Hurler syndrome and pronounced gingival hypertrophy. The disorder is caused by a defect in targeting acid hydrolases on the surface of lysosomes, which impede their entry and lead to accumulation of undigested substrates in lysosomes. The onset of the symptoms is usually in infancy, beginning in the 6th month of life. Early onset, at birth or even in utero, is a sign of severity and involves the specific dysmorphia as well as skeletal dysplasia related to hyperparathyroidism. We report on a severe neonatal form of this disorder revealed by respiratory distress with severe chest deformity. The dysmorphic syndrome, combining coarse features, pronounced gingival hypertrophy, with diffuse bone demineralization and secondary hyperparathyroidism associating significant elevation of parathyroid hormone and alkaline phosphatase with normal levels of vitamin D and calcium were characteristics of mucolipidosis type II. Recognizing this specific association of anomalies helps eliminate the differential diagnosis and establish appropriate diagnosis and care.

A pilot study of gene testing of genetic bone dysplasia using targeted next-generation sequencing

Molecular diagnosis of genetic bone dysplasia is challenging for non-expert. A targeted next-generation sequencing technology was applied to identify the underlying molecular mechanism of bone dysplasia and evaluate the contribution of these genes to patients with bone dysplasia encountered in pediatric endocrinology. A group of unrelated patients (n=82), characterized by short stature, dysmorphology and X-ray abnormalities, of which mucopolysacharidoses, GM1 gangliosidosis, mucolipidosis type II/III and achondroplasia owing to FGFR3 G380R mutation had been excluded, were recruited in this study. Probes were designed to 61 genes selected according to the nosology and classification of genetic skeletal disorders of 2010 by Illumina's online DesignStudio software. DNA was hybridized with probes and then a library was established following the standard Illumina protocols. Amplicon library was sequenced on a MiSeq sequencing system and the data were analyzed by MiSeq Reporter. Mutations of 13 different genes were found in 44 of the 82 patients (54%). Mutations of COL2A1 gene and PHEX gene were found in nine patients, respectively (9/44=20%), followed by COMP gene in 8 (18%), TRPV4 gene in 4 (9%), FBN1 gene in 4 (9%), COL1A1 gene in 3 (6%) and COL11A1, TRAPPC2, MATN3, ARSE, TRPS1, SMARCAL1, ENPP1 gene mutations in one patient each (2% each). In conclusion, mutations of COL2A1, PHEX and COMP gene are common for short stature due to bone dysplasia in outpatient clinics in pediatric endocrinology. Targeted next-generation sequencing is an efficient way to identify the underlying molecular mechanism of genetic bone dysplasia.

AB124. Mucolipidosis type II: clinical features and laboratories.

Background I-cell disease (Mucolipidosis II) is a rare lysosomal storage disorder caused by the deficiency of N-acetylglucosamine-l-phosphotransferase, an enzyme that transfers phosphate groups onto oligosaccharide units of lysosomal enzyme precursors. Due to the absence of transferase activity, the common phosphomannose recognition marker of acid hydrolases is not generated, and the enzymes are not targeted to the lysosomes I. As a consequence the enzymes are secreted into the extracellular space, and high activities can be found in the serum, cerebrospinal fluid and urine of the patients, whereas inside the cells (fibroblasts) the enzyme levels are considerably reduced. Mucolipidosis is also known as I-cell disease because of the coarse granular cytoplasmic inclusions seen in cultured skin fibroblasts which are large lysosomes containing heterogeneous material.

The mucolipidosis IV Ca2+ channel TRPML1 (MCOLN1) is regulated by the TOR kinase.

Autophagy is a complex pathway regulated by numerous signalling events that recycles macromolecules and may be perturbed in lysosomal storage disorders (LSDs). During autophagy, aberrant regulation of the lysosomal Ca(2+) efflux channel TRPML1 [transient receptor potential mucolipin 1 (MCOLN1)], also known as MCOLN1, is solely responsible for the human LSD mucolipidosis type IV (MLIV); however, the exact mechanisms involved in the development of the pathology of this LSD are unknown. In the present study, we provide evidence that the target of rapamycin (TOR), a nutrient-sensitive protein kinase that negatively regulates autophagy, directly targets and inactivates the TRPML1 channel and thereby functional autophagy, through phosphorylation. Further, mutating these phosphorylation sites to unphosphorylatable residues proved to block TOR regulation of the TRPML1 channel. These findings suggest a mechanism for how TOR activity may regulate the TRPML1 channel.

The mucolipin-2 (TRPML2) ion channel: a tissue-specific protein crucial to normal cell function.

The discovery of the TRPML subfamily of ion channels has created an exciting niche in the fields of membrane trafficking, signal transduction, autophagy, and metal homeostasis. The TRPML protein subfamily consists of three members, TRPML1, TRPML2, and TRPML3, which are encoded by MCOLN1, MCOLN2, and MCOLN3 genes, respectively. They are non-selective cation channels with six predicted transmembrane domains and intracellular amino- and carboxyl-terminus regions. They localize to the plasma membrane, endosomes, and lysosomes of cells. TRPML1 is associated with the human lysosomal storage disease known as mucolipidosis type IV (MLIV), but TRPML2 and TRPML3 have not been linked with a human disease. Although TRPML1 is expressed in many tissues, TRPML3 is expressed in a varied but limited set of tissues, while TRPML2 has a more limited expression pattern where it is mostly detected in lymphoid and myeloid tissues. This review focuses on TRPML2 because it appears to play an important, yet unrecognized role in the immune system. While the evidence has been mostly indirect, we present and discuss relevant data that strengthen the connection of TRPML2 with cellular immunity. We also discuss the functional redundancy between the TRPML proteins, and how such features could be exploited as a potential therapeutic strategy for MLIV disease. We present evidence that TRPML2 expression may complement certain phenotypic alterations in MLIV cells and briefly examine the challenges of functional complementation. In conclusion, the function of TRPML2 still remains obscure, but emerging data show that it may serve a critical role in immune cell development and inflammatory responses.

Site-1 protease-activated formation of lysosomal targeting motifs is independent of the lipogenic transcription control

Site-1 protease (S1P) cleaves membrane-bound lipogenic sterol regulatory element-binding proteins (SREBPs) and the α/β-subunit precursor protein of the N-acetylglucosamine-1-phosphotransferase forming mannose 6-phosphate (M6P) targeting markers on lysosomal enzymes. The translocation of SREBPs from the endoplasmic reticulum (ER) to the Golgi-resident S1P depends on the intracellular sterol content, but it is unknown whether the ER exit of the α/β-subunit precursor is regulated. Here, we investigated the effect of cholesterol depletion (atorvastatin treatment) and elevation (LDL overload) on ER-Golgi transport, S1P-mediated cleavage of the α/β-subunit precursor, and the subsequent targeting of lysosomal enzymes along the biosynthetic and endocytic pathway to lysosomes. The data showed that the proteolytic cleavage of the α/β-subunit precursor into mature and enzymatically active subunits does not depend on the cholesterol content. In either treatment, lysosomal enzymes are normally decorated with M6P residues, allowing the proper sorting to lysosomes. In addition, we found that, in fibroblasts of mucolipidosis type II mice and Niemann-Pick type C patients characterized by aberrant cholesterol accumulation, the proteolytic cleavage of the α/β-subunit precursor was not impaired. We conclude that S1P substrate-dependent regulatory mechanisms for lipid synthesis and biogenesis of lysosomes are different.

Mucolipidosis types II and III and non-syndromic stuttering are associated with different variants in the same genes.

Homozygous mutations in GNPTAB and GNPTG are classically associated with mucolipidosis II (ML II) alpha/beta and mucolipidosis III (ML III) alpha/beta/gamma, which are rare lysosomal storage disorders characterized by multiple pathologies. Recently, variants in GNPTAB, GNPTG, and the functionally related NAGPA gene have been associated with non-syndromic persistent stuttering. In a worldwide sample of 1013 unrelated individuals with non-syndromic persistent stuttering we found 164 individuals who carried a rare non-synonymous coding variant in one of these three genes. We compared the frequency of these variants with those in population-matched controls and genomic databases, and their location with those reported in mucolipidosis. Stuttering subjects displayed an excess of non-synonymous coding variants compared to controls and individuals in the 1000 Genomes and Exome Sequencing Project databases. We identified a total of 81 different variants in our stuttering cases. Virtually all of these were missense substitutions, only one of which has been previously reported in mucolipidosis, a disease frequently associated with complete loss-of-function mutations. We hypothesize that rare non-synonymous coding variants in GNPTAB, GNPTG, and NAGPA may account for as much as 16% of persistent stuttering cases, and that variants in GNPTAB and GNPTG are at different sites and may in general, cause less severe effects on protein function than those in ML II alpha/beta and ML III alpha/beta/gamma.

Intracellular Zinc Dyshomeostasis Caused by a Disrupted TRPML1‐TMEM163 Protein Interaction

Dysfunctional Mucolipin‐1 (TRPML1) ion channel protein causes the human lysosomal storage disorder Mucolipidosis type IV (MLIV). Cells affected by MLIV display higher intracellular zinc levels compared to normal cells; however, the mechanism behind this zinc accumulation is unknown. We recently identified a putative zinc transporter called transmembrane‐163 protein (TMEM163) as an interacting partner for TRPML1. We hypothesize that TMEM163′s interaction with TRPML1 influences its subcellular localization. We also propose that the interaction between the two proteins regulates intracellular zinc homeostasis. To examine their functional relationship, we created N‐terminus deletion mutants of TMEM163. Co‐immunoprecipitation shows disruption of TRPML1 binding to the deletion mutants compared against wild‐type (WT) TMEM163. Cell surface biotinylation reveals that plasma membrane (PM) localization of TMEM163 mutants increased upon co‐expression with TRPML1 in human embryonic kidney (HEK)‐293 cells, while WT TMEM163 PM localization decreases with co‐expressed TRPML1, suggesting that TRPML1 influences TMEM163′s internalization. Spectrofluorometric analysis of HEK‐293 cells co‐expressing TMEM163 mutants and TRPML1 shows an increase in intracellular zinc levels relative to control when the cells are transiently exposed to zinc. Overall, these data suggest that the loss of TMEM163 protein interaction with TRPML1 results in its abnormal subcellular localization, which consequently affects intracellular zinc homeostasis. Future studies characterizing the role of TMEM163 on MLIV pathology could further explain the contribution of zinc in progressive cell death and open new research avenues to develop potential therapies for the disease.

Fusion of Lysosomes with Secretory Vesicle Leads to Excessive Uncontrolled Exocytosis in Mucolipidosis Type IV

Mutations in TRPML1 cause the lysosomal storage disease (LSD) Mucolipidosis type IV (MLIV), which is characterized by neurodegeneration, muscular hypotonia corneal opacity, achlorhydia, anemia and severe psychomotor deficiency with impaired neuromuscular junctions. The role of the TRP channel TRPML1 in cell function and how mutations in TRPML1 cause MLIV are not well understood. Studies on the causes of MLIV are focused on the potential role of TRPML1 in constitutive membrane trafficking to and from the lysosomes. However, the role of TRPML1 in secretory cells that their cardinal function is regulated exocytosis has not been studied. Here, we analyzed several forms of regulated exocytosis in neurons and secretory epithelia in a knockout mouse model of TRPML1 and, unexpectedly, found excessive exocytosis due to marked enlargement of synaptic vesicles and secretory granules due to fusion with lysosomes. As a result, Trpml1−/− neurons maintain high basal and stimulated exocytosis of the neurotransmitter and neurotoxin glutamate, which may account for the neurodegeneration in ML4. Trpml1−/− pancreatic and salivary glands acini show high Ca2+− and cAMP-stimulated exocytosis, resulting in pancreatitis. These features were not found in another model of LSD, the Niemann-Pick disease type C1 mouse model. These findings indicate that a major role of TRPML1 is to guard against pathological fusion of lysosomes with other intracellular organelles, including secretory vesicles, and suggest a new approach towards developing treatment for MLIV.

Impaired myelination and reduced brain ferric iron in the mouse model of mucolipidosis IV.

ABSTRACTMucolipidosis type IV (MLIV) is a lysosomal storage disease caused by mutations in the MCOLN1 gene, which encodes the lysosomal transient receptor potential ion channel mucolipin-1 (TRPML1). MLIV causes impaired motor and cognitive development, progressive loss of vision and gastric achlorhydria. How loss of TRPML1 leads to severe psychomotor retardation is currently unknown, and there is no therapy for MLIV. White matter abnormalities and a hypoplastic corpus callosum are the major hallmarks of MLIV brain pathology. Here, we report that loss of TRPML1 in mice results in developmental aberrations of brain myelination as a result of deficient maturation and loss of oligodendrocytes. Defective myelination is evident in Mcoln1−/− mice at postnatal day 10, an active stage of postnatal myelination in the mouse brain. Expression of mature oligodendrocyte markers is reduced in Mcoln1−/− mice at postnatal day 10 and remains lower throughout the course of the disease. We observed reduced Perls' staining in Mcoln1−/− brain, indicating lower levels of ferric iron. Total iron content in unperfused brain is not significantly different between Mcoln1−/− and wild-type littermate mice, suggesting that the observed maturation delay or loss of oligodendrocytes might be caused by impaired iron handling, rather than by global iron deficiency. Overall, these data emphasize a developmental rather than a degenerative disease course in MLIV, and suggest that there should be a stronger focus on oligodendrocyte maturation and survival to better understand MLIV pathogenesis and aid treatment development.

Mucolipin co-deficiency causes accelerated endolysosomal vacuolation of enterocytes and failure-to-thrive from birth to weaning.

During the suckling period, intestinal enterocytes are richly endowed with endosomes and lysosomes, which they presumably utilize for the uptake and intracellular digestion of milk proteins. By weaning, mature intestinal enterocytes replace those rich in lysosomes. We found that mouse enterocytes before weaning express high levels of two endolysosomal cation channels, mucolipins 3 and 1 -products of Trpml3 and Trpml1 genes; moreover neonatal enterocytes of mice lacking both mucolipins (Trpml3−/−;Trpml1−/−) vacuolated pathologically within hours of birth and remained so until weaning. Ultrastructurally and chemically these fast-forming vacuoles resembled those that systemically appear in epithelial cells of mucolipidosis type IV (MLIV) patients, which bear mutations in Trpml1. Hence, lack of both mucolipins 1 and 3 causes an accelerated MLIV-type of vacuolation in enterocytes. The vacuoles were aberrant hybrid organelles with both endosomal and lysosomal components, and were not generated by alterations in endocytosis or exocytosis, but likely by an imbalance between fusion of lysosomes and endosomes and their subsequent scission. However, upon extensive vacuolation enterocytes displayed reduced endocytosis from the intestinal lumen, a defect expected to compromise nutrient uptake. Mice lacking both mucolipins suffered a growth delay that began after birth and continued through the suckling period but recovered after weaning, coinciding with the developmental period of enterocyte vacuolation. Our results demonstrate genetic redundancy between lysosomal mucolipins 3 and 1 in neonatal enterocytes. Furthermore, our Trpml3−/−;Trpml1−/− mice represent a polygenic animal model of the poorly-understood, and often intractable, neonatal failure-to-thrive with intestinal pathology. Our results implicate lysosomes in neonatal intestinal pathologies, a major cause of infant mortality worldwide, and suggest transient intestinal dysfunction might affect newborns with lysosomal storage disorders. Finally, we conclude that mucolipin-endowed lysosomes in the young play an evolutionarily-conserved role in the intracellular digestion of maternally-provided nutrients, whether milk in mammals or yolk in oviparous species.

PAX5 is the transcriptional activator of mucolipin-2 (MCOLN2) gene

Transient receptor potential mucolipin (TRPML) proteins belong to the TRP superfamily of non-selective cation channels. The TRPML1, -2, and -3 proteins are encoded by Mucolipin (MCOLN)-1, -2 and -3 genes, respectively. TRPML1 has been associated with mucolipidosis type IV (MLIV), while no disease phenotype has been linked with TRPML2 or -3 protein. The TRPML proteins share high sequence similarities, form hetero-tetramers, and serve in membrane trafficking, autophagy, and metal homeostasis. Previous studies suggest that TRPML2 serves a role in the immune system; however, the evidence is mostly indirect. We hypothesize that if TRPML2 is involved in immune function its expression would be likely regulated by an immune-associated transcription factor protein. Thus, we set out to identify the core promoter region and the transcription factor responsible for MCOLN2 gene expression. Using dual-luciferase assay and over-expression analyses, we reveal for the first time that B-cell lineage specific activator protein (BSAP), also known as paired box 5 (PAX5), controls MCOLN2 expression. Specifically, heterologous expression of PAX5 in HEK-293 cells significantly increased endogenous MCOLN2 transcript and TRPML2 protein levels, while RNA interference targeting endogenous PAX5 reduced its effect. Site-directed mutagenesis studies showed that the core promoter and PAX5 binding region to be between −79 and −60 base pairs upstream of the transcriptional start site. Thus, our findings add to a growing list of evidence for TRPML2's possible involvement in the immune system. The knowledge gained from this study could be used to further characterize the role of TRPML2 in B-cell development and function.

Differential mechanisms of action of the mucolipin synthetic agonist, ML-SA1, on insect TRPML and mammalian TRPML1

Mucolipin synthetic agonist 1 (ML-SA1) was recently identified to activate mammalian TRPML channels and shown to alleviate lipid accumulation in lysosomes of cellular models of lysosome storage diseases, mucolipidosis type IV (MLIV) and Niemann–Pick's disease type C (NPC). Owning to its potential use in complimenting genetic studies in Drosophila melanogaster to elucidate the cellular and physiological functions of TRPML channels, we examined the effect of ML-SA1 on Drosophila TRPML expressed in HEK293 cells using whole-cell, inside-out, and whole-lysosome electrophysiological recordings. We previously showed that when expressed in HEK293 cells, Drosophila TRPML was localized and functional on both plasma membrane and endolysosome. We show here that in both inside-out patches excised from the plasma membrane and whole-lysosome recordings from enlarged endolysosome vacuoles, ML-SA1 failed to activate TRPML unless exogenous phosphatidylinositol 3,5-bisphosphate [PI(3,5)P2] was applied. At 1μM ML-SA1, the sensitivity of TRPML to PI(3,5)P2 increased approximately by 10-fold and at 10μM ML-SA1, the deactivation of PI(3,5)P2-evoked TRPML currents was markedly slowed. On the other hand, constitutive activation of TRPML by a mutation that mimics the varitint-waddler (Va) mutation of mouse TRPML3 rendered the insect channel sensitive to activation by ML-SA1 alone. Moreover, different from the insect TRPML, mouse TRPML1 was readily activated by ML-SA1 independent of PI(3,5)P2. Thus, our data reveal that while ML-SA1 acts as a true agonist at mouse TRPML1, it behaves as an allosteric activator of the Drosophila TRPML, showing dependence on and the ability to stabilize open conformation of the insect channels.

Cellular zinc levels are modulated by TRPML1-TMEM163 interaction.

Mucolipidosis type IV (MLIV) is caused by loss of function mutations in the TRPML1 ion channel. We previously reported that tissue zinc levels in MLIV were abnormally elevated; however, the mechanism behind this pathologic accumulation remains unknown. Here, we identify transmembrane (TMEM)-163 protein, a putative zinc transporter, as a novel interacting partner for TRPML1. Evidence from yeast two-hybrid, tissue expression pattern, co-immunoprecipitation, mass spectrometry and confocal microscopy studies confirmed the physical association of TMEM163 with TRPML1. This interaction is disrupted when a part of TMEM163's N-terminus was deleted. Further studies to define the relevance of their interaction revealed that the plasma membrane (PM) levels of TMEM163 significantly decrease when TRPML1 is co-expressed in HEK-293 cells, while it mostly localizes within the PM when co-expressed with a mutant TRPML1 that distributes mostly in the PM. Meanwhile, co-expression of TMEM163 does not alter TRPML1 channel activity, but its expression levels in MLIV patient fibroblasts are reduced, which correlate with marked accumulation of zinc in lysosomes when these cells are acutely exposed to exogenous zinc (100 μM). When TMEM163 is knocked down or when TMEM163 and TRPML1 are co-knocked down in HEK-293 cells treated overnight with 100 nm zinc, the cells have significantly higher intracellular zinc levels than untreated control. Overall, these findings suggest that TMEM163 and TRPML1 proteins play a critical role in cellular zinc homeostasis, and thus possibly explain a novel mechanism for the pathological overload of zinc in MLIV disease.

A small molecule restores function to TRPML1 mutant isoforms responsible for mucolipidosis type IV

Mucolipidosis type IV (MLIV) is an autosomal recessive lysosomal storage disorder often characterized by severe neurodevelopmental abnormalities and neuro-retinal degeneration. Mutations in the TRPML1 gene are causative for MLIV. We used lead optimization strategies to identify--and MLIV patient fibroblasts to test--small-molecule activators for their potential to restore TRPML1 mutant channel function. Using the whole-lysosome planar patch-clamp technique, we found that activation of MLIV mutant isoforms by the endogenous ligand PI(3,5)P2 is strongly reduced, while activity can be increased using synthetic ligands. We also found that the F465L mutation renders TRPML1 pH insensitive, while F408Δ impacts synthetic ligand binding. Trafficking defects and accumulation of zinc in lysosomes of MLIV mutant fibroblasts can be rescued by the small molecule treatment. Collectively, our data demonstrate that small molecules can be used to restore channel function and rescue disease associated abnormalities in patient cells expressing specific MLIV point mutations.

Outcomes after Hematopoietic Stem Cell Transplantation for Children with I-Cell Disease

Mucolipidosis type II (MLII), or I-cell disease, is a rare but severe disorder affecting localization of enzymes to the lysosome, generally resulting in death before the 10th birthday. Although hematopoietic stem cell transplantation (HSCT) has been used to successfully treat some lysosomal storage diseases, only 2 cases have been reported on the use of HSCT to treat MLII. For the first time, we describe the combined international experience in the use of HSCT for MLII in 22 patients. Although 95% of the patients engrafted, overall survival was low, with only 6 patients (27%) alive at last follow-up. The most common cause of death post-transplant was cardiovascular complications, most likely due to disease progression. Survivors were globally delayed in development and often required complex medical support, such as gastrostomy tubes for nutrition and tracheostomy with mechanical ventilation. Although HSCT has demonstrated efficacy in treating some lysosomal storage disorders, the neurologic outcome and survival for patents with MLII were poor. Therefore, new medical and cellular therapies should be sought for these patients.

TGN exit of the cation-independent mannose 6-phosphate receptor does not require acid hydrolase binding.

The cation-independent mannose 6-phosphate (Man-6-P) receptor (CI-MPR) binds newly synthesized, Man-6-P-containing lysosomal acid hydrolases in the trans-Golgi network (TGN) for clathrin-mediated transport to endosomes. It has remained unresolved, however, whether acid hydrolase binding is required for exit of the CI-MPR from the TGN. To address this question we used a B cell line derived from a Mucolipidosis type II (MLII)/I-cell disease patient. In MLII patients, acid hydrolases do not acquire the Man-6-P recognition marker and as a consequence do not bind to the CI-MPR. This causes secretion of the majority of the acid hydrolases and a decreased lysosomal activity resulting in typical inclusion bodies. In agreement herewith, ultrastructural analysis of the MLII patient derived B cells showed numerous inclusion bodies with undigested material, which we defined as autolysosomes. By quantitative immuno-electron microscopy we then studied the distribution of the CI-MPR in these cells. We found that the level of co-localization of TGN-localized CI-MPR and clathrin was similar in MLII and control B cells. Moreover, the CI-MPR was readily found in endosomes of MLII cells and the TGN-to-early endosome ratio of CI-MPR labeling was unaltered. These data show that there is no block in TGN exit of the CI-MPR in the absence of Man-6-P-modified acid hydrolases. Notably, late endosomes and inclusion bodies in MLII B cells contained increased levels of the CI-MPR, which likely reflects the reduced degradative capacity of these compartments.

Systemic accumulation of undigested lysosomal metabolites in an autopsy case of mucolipidosis type II; autophagic dysfunction in cardiomyocyte

Mucolipidosis type II is an autosomal recessive lysosomal storage disease caused by N-acetylglucosamine-1-phosphotransferese deficiency. We report here pathological findings of an autopsy case of mucolipidosis type II. The patient was an 8-year-old boy with mucolipidosis type II and was complicated with hypertrophic cardiomyopathy. He suddenly developed progressive respiratory failure and finally died. At autopsy, systemic accumulation of undigested lysosomal metabolites was prominent, particularly in the heart, lungs, and dorsal root ganglion. In cardiomyocyte, LC3, an autophagy marker, was positive in the cytoplasm. Ubiquitin, p62, K48 polyubiquitin, and K63 polyubiquitin were also positive in the cytoplasm. Our findings suggest that autophagic dysfunction might be associated with the cardiomyopahty of mucolipidosis type II.

Cellular zinc levels are influenced by the interaction between the mucolipidosis IV‐associated TRPML1 protein and TMEM163 protein (996.5)

Dysfunctional Mucolipin‐1 (TRPML1) ion channel protein causes the human lysosomal storage disorder Mucolipidosis type IV (MLIV). Cells affected by MLIV have significantly higher intracellular zinc levels compared to normal cells; however, the mechanism of zinc elevation remains unknown. Using a membrane‐based yeast two‐hybrid technique, we identified a putative zinc‐binding protein called transmembrane‐163 protein (TMEM163) as an interacting partner for TRPML1. We confirmed interaction by co‐immunoprecipitation and mass spectrometry. We hypothesized that the interaction between TMEM163 and TRPML1 plays a role in regulating TMEM163, and thus intracellular zinc. RNA interference targeting both TMEM163 and TRPML1 in SH‐SY5Y neuroblastoma cells resulted in significant increase of intracellular zinc when both proteins were knocked down. To determine how interaction of TRPML1 and TMEM163 could be responsible in regulation of intracellular zinc, we co‐expressed and analyzed expression of tagged constructs of both proteins using human embryonic kidney (HEK)‐293 cells. Evidence from cell surface biotinylation showed that co‐expressed TRPML1 resulted in reduced TMEM163 localized within the plasma membrane of HEK‐293 cells. This result possibly explains the reduction of cellular zinc flux when TRPML1 is co‐expressed with TMEM163. Overall, our data suggest that both TRPML1 and TMEM163 proteins play a role in intracellular zinc regulation. Thus, the loss of TRPML1 protein function and/or the reduction of TMEM163 protein could result in zinc dyshomeostasis in MLIV.Grant Funding Source: Supported by NIH R15‐NS070774 and CSUF Intramural Grants

Analysis of the transcriptional activation and post‐transcriptional regulation of transient receptor potential mucolipin‐2 gene (561.5)

Mucolipidosis type IV (MLIV) is a neurodegenerative disease caused by loss or dysfunction of the human transient receptor potential mucolipin 1 (TRPML1) protein. TRPML1 is a non‐selective cation channel related to two other proteins, TRPML2 and TRPML3. The high degree of sequence and functional similarities between TRPML1 and TRPML2 make TRPML2 an excellent candidate to potentially substitute for the loss of TRPML1 function in MLIV. In order to consider this possibility, we first needed to study the mechanisms that control the expression of TRPML2 gene. We cloned DNA regions of varying size upstream of the TRPML2 gene transcriptional start site (TSS) into a dual luciferase reporter assay. We identified a putative core promoter region between ‐320 and ‐287 of the TSS containing a consensus sequence for six transcription factors. Heterologous expression of the candidate TFs conferred an effect on the expression of endogenous TRPML2 transcripts compared to control. Meanwhile, we found that a specific micro‐RNA was responsible for post‐transcriptional regulation of endogenous TRPML2 transcripts as evidenced by real‐time quantitative PCR (qPCR) technique. We then screened a drug library and confirmed by real‐time qPCR that each drug candidate significantly increased the expression of endogenous TRPML2 transcripts. These results show that we could induce the expression of the TRPML2 gene through exogenous manipulation of transcriptional activators or post‐transcriptional regulators. Understanding the mechanism of TRPML2 expression is a step closer to our goal of using TRPML2 protein to substitute for the loss of TRPML1 protein function in MLIV.Grant Funding Source: Supported by NIH R15‐NS070774 and CSUF Intramural Grants