Genetically Corrected iPSC-Derived Neural Stem Cell Grafts Deliver Enzyme Replacement to Affect CNS Disease in Sanfilippo B Mice

Abstract

Sanfilippo syndrome type B (mucopolysaccharidosis type IIIB [MPS IIIB]) is a lysosomal storage disorder primarily affecting the brain that is caused by a deficiency in the enzyme α-N-acetylglucosaminidase (NAGLU), leading to intralysosomal accumulation of heparan sulfate. There are currently no treatments for this disorder. Here we report that, ex vivo, lentiviral correction of Naglu^-/- neural stem cells derived from Naglu^-/- mice (iNSCs) corrected their lysosomal pathology and allowed them to secrete a functional NAGLU enzyme that could be taken up by deficient cells. Following long-term transplantation of these corrected iNSCs into Naglu^-/- mice, we detected NAGLU activity in the majority of engrafted animals. Successfully transplanted Naglu^-/- mice showed a significant decrease in storage material, a reduction in astrocyte activation, and complete prevention of microglial activation within the area of engrafted cells and neighboring regions, with beneficial effects extending partway along the rostrocaudal axis of the brain. Our results demonstrate long-term engraftment of iNSCs in the brain that are capable of cross-correcting pathology in Naglu^-/- mice. Our findings suggest that genetically engineered iNSCs could potentially be used to deliver enzymes and treat MPS IIIB.

Keywords: MPS IIIB; lysosomal storage disorder; stem cell therapy.

Figure 1

Characterization of Induced Pluripotent Stem Cells and Neural Stem Cells (A–C) Naglu^−/− iPSCs growing on feeder mouse embryonic fibroblasts (MEFs). (A) Phase contrast image, alkaline phosphatase staining, and Oct-4 (red) staining merged with nuclear staining (DAPI, blue). Scale bars, 200 μm (phase contrast) and 400 μm (alkaline phosphatase and Oct4). (B) Real-time qPCR probing Nestin gene expression after differentiation of iPSCs to neural stem cells (iNSCs; n = 5, p = 0.0005). Mean with SD. (C) Immunostaining of iNSCs with Nestin (red). Scale bar, 500 μm. (D–F) iNSCs were further differentiated into different cell types characterized by antibodies against Map2 and Tuj-1 (neuron markers) (D), GFAP (astrocyte marker) (scale bar represents 500 μm) (E), and Olig1 (oligodendrocyte marker) (scale bars represent 100 μm) (F). Nuclear staining with DAPI (blue) was overlaid in (C)–(F). Post-acquisition processing included adjustment of brightness and contrast in (C)–(F) using Adobe Photoshop CS6 to reduce over-exposure. ***p < 0.001.

Figure 2

NAGLU Gene Therapy and Subsequent Biochemical Characterization (A) FACS analysis of Naglu^−/− iNSCs (white) transduced with NAGLU-GFP (black). (B and C) Quantifying secreted (C) and intracellular (B) NAGLU enzyme activity in iNSCs overexpressing NAGLU (N-iNSCs). Student’s t test, p < 0.0001 and p = 0.0047, respectively. (D) Cellular uptake and inhibition assay on iNSCs (Naglu^−/−) treated with supernatant collected from N-iNSCs in the presence or absence of 5 mM mannose-6-phosphate (M6P). n = 4, one-way ANOVA, p < 0.0001. (B–D) Mean with SD. Intracellular NAGLU activity is presented as units per milligram of protein, whereas the secreted NAGLU activity is presented as units per milliliter expressed as mean ± SD, where a unit is defined as the release of 1 nmol of 4-MU per hour at 37°C. **p < 0.01, ****p < 0.0001.

Figure 3

NAGLU Corrected N-iNSC Grafting after 2 Months (A) Annotated image of the parameters for intracerebroventricular (ICV, green) and intraparenchymal (PAR, blue) injections. X indicates represented injection sites. (B) Immunohistological staining of 40-μm representative sections for GFP, shown in low magnification, following ICV and intraparenchymal transplantion of N-iNSCs at birth (cells have a GFP reporter) in Naglu^−/− mice 2 months after transplantation. Post-acquisition processing included adjustments to brightness and contrast and red green blue (RGB) curves using Adobe Photoshop CS6 to improve visibility and consistency in color tone. Scale bar, 1 mm. Rostrocaudal distribution of N-iNSCs relative to the level of greatest engraftment is shown in millimeters (bottom left corner). FACS analysis showing percentage engraftment (C and D, top) and NAGLU enzyme activity assays are shown in units per milligram of protein (C and D, bottom), performed on brain lysates following ICV and intraparenchymal injection (n = 6 in each treatment).

Figure 4

Reduction of Microglial Activation in Naglu^−/− Mice Treated with Neural Stem Cells Overexpressing NAGLU (A) Schematic illustration of ICV injection (green) at the bregma (1.54 mm) and PAR injection (blue) at the bregma (−0.58 mm), demonstrating regions of analysis (red squares) relative to the site of engraftment (ICV and PAR), including the motor cortex, striatum, and ventral forebrain. (B) Representative bright-field images taken at a low magnification of half-brain coronal sections of immunohistochemical staining of CD68 in a mouse injected with N-iNSCs (−/− treated) compared with unaffected heterozygous (unaffected) and vehicle-injected Naglu^−/− mice (−/− vehicle). Scale bar, 1 mm. The locations of ICV and intraparenchymal injections are outlined by red dotted lines. The blue dotted lines outline regions where CD68 staining is less pronounced, indicating a reduction of microglial activation. (C) Representative bright-field images of the motor cortex (1), striatum (2), and ventral forebrain (3) of immunohistological staining for CD68 in −/− vehicle compared with unaffected mice and in −/− treated mice upon ICV and intraparenchymal injection. Scale bars, 100 μm. The blue dotted lines highlight the difference in CD68 immunoreactivity close to the ventricle (yellow box) versus farther away from the ventricle (dark blue box) in ICV-injected brains. Inset images were taken at higher magnification to highlight the differences in morphology of CD68-stained microglia. Scale bars, 20 μm. Post-acquisition processing was applied to all images and included adjustments to brightness and contrast and RGB curves using Adobe Photoshop CS6 to improve visibility and consistency in color tone. The histograms on the right show the area of CD68 immunoreactivity for each group, measured. *p < 0.05, **p < 0.01, ***p < 0.001; two-tailed, unpaired parametric t test. Values are shown as mean ± SEM (n = 3 mice per group). Mean with SEM. For p values, see Tables 1 and 2.

Figure 5

NAGLU Corrected N-iNSCs Grafting and Characterization of Enzyme Activity at 9 Months (A) Immunohistological staining of 40-μm representative sections for GFP, shown at low magnification, following PAR injection of N-iNSCs into Naglu^−/− mice. Post-acquisition processing included adjustments to brightness and contrast and RGB curves using Adobe Photoshop CS6 to improve visibility and consistency in color tone. Scale bar, 1 mm. (B) Schematic diagram depicting how the brains were divided. Brains were dissected sagittally along the midline first. One brain hemisphere was for histology, and the other brain hemisphere was further sectioned into 2-mm-thick coronal slices in each animal. For NAGLU and hexosaminidase (HEX) activity assays, brain sections 1 and 2 and 5 and 6 were pooled. The blue dots represent the approximate intraparenchymal injection sites. (C and D) Enzymatic activity of NAGLU (C) and HEX (D), respectively, in Naglu^−/− mice with N-iNSCs (−/− treated) or saline (−/− vehicle) compared with heterozygous control mice (unaffected). All bars show mean ± SD (n = 10–12 mice per group). Mean with SD. Two-tailed, unpaired parametric t tests were used between (−/− treated) or saline (−/− vehicle) groups.*p < 0.05, **p < 0.01, ****p < 0.0001.

Figure 6

Correction of Neuropathology and Storage Accumulation in Naglu^−/− Mice Treated with Neural Stem Cells Overexpressing NAGLU N-iNSCs at 9 Months (A–C) Representative bright-field images of half-brain coronal sections from heterozygous control mice (unaffected) and mice injected with saline (−/− vehicle) or N-iNSCs (−/− treated). Images were taken at three levels along the rostrocaudal axis (rostral, middle, and caudal) and immunohistochemically stained for CD68 (A), GFAP (B), and Lamp 1 (C), respectively. Numbered boxes show images taken at higher magnification from three specific areas within each section (boxes 1–3, outlined at lower magnification, top). The same three areas were analyzed for GFAP and Lamp 1. Post-acquisition processing was applied to all images and included adjustments to brightness and contrast and RGB curves using Adobe Photoshop CS6 to improve visibility and consistency in color tone. Scale bars, 1 mm.