Among the known genetic risk factors for Parkinson disease, mutations in GBA1, the gene responsible for the lysosomal disorder Gaucher disease, are the most common. This genetic link has directed attention to the role of the lysosome in the pathogenesis of parkinsonism. To study how glucocerebrosidase impacts parkinsonism and to evaluate new therapeutics, we generated induced human pluripotent stem cells from four patients with Type 1 (non-neuronopathic) Gaucher disease, two with and two without parkinsonism, and one patient with Type 2 (acute neuronopathic) Gaucher disease, and differentiated them into macrophages and dopaminergic neurons. These cells exhibited decreased glucocerebrosidase activity and stored the glycolipid substrates glucosylceramide and glucosylsphingosine, demonstrating their similarity to patients with Gaucher disease. Dopaminergic neurons from patients with Type 2 and Type 1 Gaucher disease with parkinsonism had reduced dopamine storage and dopamine transporter reuptake. Levels of ␣-synuclein, a protein present as aggregates in Parkinson disease and related synucleinopathies, were selectively elevated in neurons from the patients with parkinsonism or Type 2 Gaucher disease. The cells were then treated with NCGC607, a small-molecule noninhibitory chaperone of glucocerebrosidase identified by high-throughput screening and medicinal chemistry structure optimization. This compound successfully chaperoned the mutant enzyme, restored glucocerebrosidase activity and protein levels, and reduced glycolipid storage in both iPSC-derived macrophages and dopaminergic neurons, indicating its potential for treating neuronopathic Gaucher disease. In addition, NCGC607 reduced ␣-synuclein levels in dopaminergic neurons from the patients with parkinsonism, suggesting that noninhibitory small-molecule chaperones of glucocerebrosidase may prove useful for the treatment of Parkinson disease. Key words: ␣-synuclein; dopaminergic neurons; glucocerebrosidase; induced pluripotent stem cells; parkinsonism; pharmacological chaperone Significance StatementBecause GBA1 mutations are the most common genetic risk factor for Parkinson disease, dopaminergic neurons were generated from iPSC lines derived from patients with Gaucher disease with and without parkinsonism. These cells exhibit deficient enzymatic activity, reduced lysosomal glucocerebrosidase levels, and storage of glucosylceramide and glucosylsphingosine. Lines generated from the patients with parkinsonism demonstrated elevated levels of ␣-synuclein. To reverse the observed phenotype, the neurons were treated with a novel noninhibitory glucocerebrosidase chaperone, which successfully restored glucocerebrosidase activity and protein levels and reduced glycolipid storage. In addition, the small-molecule chaperone reduced ␣-synuclein levels in dopaminergic neurons, indicating that chaperoning glucocerebrosidase to the lysosome may provide a novel therapeutic strategy for both Parkinson disease and neuronopathic forms of Gaucher disease.

SummaryGaucher disease, the inherited deficiency of lysosomal glucocerebrosidase, is characterized by the presence of glucosylcer‐amide macrophages, the accumulation of glucosylceramide in lysosomes and the secretion of inflammatory cytokines. However, the connection between this lysosomal storage and inflammation is not clear. Studying macrophages derived from peripheral monocytes from patients with type 1 Gaucher disease with genotype N370S/N370S, we confirmed an increased secretion of interleukins IL‐1β and IL‐6. In addition, we found that activation of the inflammasome, a multiprotein complex that activates caspase‐1, led to the maturation of IL‐1β in Gaucher macrophages. We show that inflammasome activation in these cells is the result of impaired autophagy. Treatment with the small‐molecule glucocerebrosidase chaperone NCGC758 reversed these defects, inducing autophagy and reducing IL‐1β secretion, confirming the role of the deficiency of lysosomal glucocerebrosidase in these processes. We found that in Gaucher macrophages elevated levels of the autophagic adaptor p62 prevented the delivery of inflammasomes to autophagosomes. This increase in p62 led to activation of p65‐NF‐kB in the nucleus, promoting the expression of inflammatory cytokines and the secretion of IL‐1β. This newly elucidated mechanism ties lysosomal dysfunction to inflammasome activation, and may contribute to the massive organomegaly, bone involvement and increased susceptibility to certain malignancies seen in Gaucher disease. Moreover, this link between lysosomal storage, impaired autophagy, and inflammation may have implications relevant to both Parkinson disease and the aging process. Defects in these basic cellular processes may also provide new therapeutic targets.

Haematopoietic stem cells (HSCs) are maintained by bone marrow (BM) niches in vivo 1 , 2 , but the ability of niche cells to maintain HSCs ex vivo is markedly diminished. Expression of niche factors by Nestin-GFP + mesenchymal-derived stromal cells (MSCs) is downregulated upon culture, suggesting that transcriptional rewiring may contribute to this reduced HSC maintenance potential. Using an RNA sequencing screen, we identified 5 transcription factors ( Klf7 , Ostf1 , Xbp1 , Irf3 , Irf7 ) that restored HSC niche function in cultured BM-derived MSCs. These revitalized MSCs (rMSCs) exhibited enhanced synthesis of HSC niche factors while retaining their mesenchymal differentiation capacity. In contrast to HSCs co-cultured with control MSCs, HSCs expanded with rMSCs showed higher repopulation capacity and protected lethally irradiated recipient mice. Competitive reconstitution assays revealed ~7-fold expansion of functional HSCs by rMSCs. rMSCs prevented the accumulation of DNA damage in cultured HSCs, a hallmark of ageing and replication stress. Analysis of the reprogramming mechanisms uncovered a role for myocyte enhancer factor 2c ( Mef2c ) in the revitalization of MSCs. These results provide insight in the transcriptional regulation of the niche with implications for stem cell-based therapies.

Class I Basic Helix-Loop-Helix (bHLH) transcription factors form homodimers or heterodimers with class II bHLH proteins. While bHLH heterodimers are known to have diverse roles, little is known about the role of class I homodimers. In this manuscript, we show that linked a dimer of Daughterless (Da), the only Drosophila class I bHLH protein, activates Atonal (Ato) expression and retinal neuron differentiation synergistically with the retinal determination factor Eyeless (Ey). The HLH protein Extramacrocheate (Emc), which forms heterodimer with Da, antagonizes the synergistic activation from Da but not the Da-Da linked dimer with Ey. We show that Da directly interacts with Ey and promotes Ey binding to the Ey binding site in the Ato 3′ enhancer. Interestingly, the Ey binding site in the Ato 3′ enhancer contains an embedded E-box that is also required for the synergistic activation by Ey and Da. Finally we show that mammalian homologs of Ey and Da can functionally replace their Drosophila counterparts to synergistically activate the Ato enhancer, suggesting that the observed function is evolutionary conserved.

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Induced pluripotent stem cells (iPSCs) have provided new opportunities to explore the cell biology and pathophysiology of human diseases, and the lysosomal storage disorder research community has been quick to adopt this technology. Patient-derived iPSC models have been generated for a number of lysosomal storage disorders, including Gaucher disease, Pompe disease, Fabry disease, metachromatic leukodystrophy, the neuronal ceroid lipofuscinoses, Niemann-Pick types A and C1, and several of the mucopolysaccharidoses. Here, we review the strategies employed for reprogramming and differentiation, as well as insights into disease etiology gleaned from the currently available models. Examples are provided to illustrate how iPSC-derived models can be employed to develop new therapeutic strategies for these disorders. We also discuss how models of these rare diseases could contribute to an enhanced understanding of more common neurodegenerative disorders such as Parkinson’s disease, and discuss key challenges and opportunities in this area of research.

Gaucher disease, the inherited deficiency of lysosomal glucocerebrosidase, is characterized by the presence of glucosylceramide-laden macrophages resulting from impaired digestion of aged erythrocytes or apoptotic leukocytes. Studies of macrophages from patients with type 1 Gaucher disease with genotypes N370S/N370S, N370S/L444P or N370S/c.84dupG revealed that Gaucher macrophages have impaired efferocytosis resulting from reduced levels of p67phox and Rab7. The decreased Rab7 expression leads to impaired fusion of phagosomes with lysosomes. Moreover, there is defective translocation of p67phox to phagosomes, resulting in reduced intracellular production of reactive oxygen species. These factors contribute to defective deposition and clearance of apoptotic cells in phagolysosomes, which may have an impact on the inflammatory response and contribute to the organomegaly and inflammation seen in patients with Gaucher disease.

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