Lewy Body-like Inclusions in Human Midbrain Organoids Carrying Glucocerebrosidase and α-Synuclein Mutations

Objective

We utilized human midbrain‐like organoids (hMLOs) generated from human pluripotent stem cells carrying glucocerebrosidase gene (GBA1) and α‐synuclein (α‐syn; SNCA) perturbations to investigate genotype‐to‐phenotype relationships in Parkinson disease, with the particular aim of recapitulating α‐syn– and Lewy body–related pathologies and the process of neurodegeneration in the hMLO model.

Methods

We generated and characterized hMLOs from GBA1^−/− and SNCA overexpressing isogenic embryonic stem cells and also generated Lewy body–like inclusions in GBA1/SNCA dual perturbation hMLOs and conduritol‐b‐epoxide–treated SNCA triplication hMLOs.

Results

We identified for the first time that the loss of glucocerebrosidase, coupled with wild‐type α‐syn overexpression, results in a substantial accumulation of detergent‐resistant, β‐sheet–rich α‐syn aggregates and Lewy body–like inclusions in hMLOs. These Lewy body–like inclusions exhibit a spherically symmetric morphology with an eosinophilic core, containing α‐syn with ubiquitin, and can also be formed in Parkinson disease patient–derived hMLOs. We also demonstrate that impaired glucocerebrosidase function promotes the formation of Lewy body–like inclusions in hMLOs derived from patients carrying the SNCA triplication.

Interpretation

Taken together, the data indicate that our hMLOs harboring 2 major risk factors (glucocerebrosidase deficiency and wild‐type α‐syn overproduction) of Parkinson disease provide a tractable model to further elucidate the underlying mechanisms for progressive Lewy body formation. ANN NEUROL 2021;90:490–505

CDK5RAP3 is a co-factor for the oncogenic transcription factor STAT3

The transcription factor STAT3 regulates genes governing critical cellular processes such as proliferation, survival, and self-renewal. While STAT3 transcriptional function is activated rapidly and transiently in response to physiologic signals, through a variety of mechanisms it can become constitutively activated in the pathogenesis of cancer. This leads to chronic expression of genes that underlie malignant cellular behavior. However, STAT3 is known to interact with other proteins, which may modulate its function. Understanding these interactions can provide insights into novel aspects of STAT3 function and may also suggest strategies to therapeutically target the large number of cancers driven by constitutively activated STAT3. To identify critical modulators of STAT3 transcriptional function, we performed an RNA-interference based screen in a cell-based system that allows quantitative measurement of STAT3 activity. From this approach, we identified CDK5 kinase regulatory-subunit associated protein 3 (CDK5RAP3) as an enhancer of STAT3-dependent gene expression. We found that STAT3 transcriptional function is modulated by CDK5RAP3 in cancer cells, and silencing CDK5RAP3 reduces STAT3-mediated tumorigenic phenotypes including clonogenesis and migration. Mechanistically, CDK5RAP3 binds to STAT3-regulated genomic loci, in a STAT3-dependent manner. In primary human breast cancers, the expression of CDK5RAP3 expression was associated with STAT3 gene expression signatures as well as the expression of individual STAT3 target genes. These findings reveal a novel aspect of STAT3 transcriptional function and potentially provide both a biomarker of enhanced STAT3-dependent gene expression as well as a unique mechanism to therapeutically target STAT3.

Midbrain-like Organoids from Human Pluripotent Stem Cells Contain Functional Dopaminergic and Neuromelanin-Producing Neurons

Recent advances in 3D culture systems have led to the generation of brain organoids that resemble different human brain regions; however, a 3D organoid model of the midbrain containing functional midbrain dopaminergic (mDA) neurons has not been reported. We developed a method to differentiate human pluripotent stem cells into a large multicellular organoid-like structure that contains distinct layers of neuronal cells expressing characteristic markers of human midbrain. Importantly, we detected electrically active and functionally mature mDA neurons and dopamine production in our 3D midbrain-like organoids (MLOs). In contrast to human mDA neurons generated using 2D methods or MLOs generated from mouse embryonic stem cells, our human MLOs produced neuromelanin-like granules that were structurally similar to those isolated from human substantia nigra tissues. Thus our MLOs bearing features of the human midbrain may provide a tractable in vitro system to study the human midbrain and its related diseases.

Comparative hepatoprotective effects of tocotrienol analogs against drug-induced liver injury

Oxidative stress plays a major part in the pathogenesis of drug-induced liver injury. Yet, overcoming it with other xenobiotics impose additional risks. In this study, we consider the use of natural-occurring and purified Vitamin E analogs as hepatoprotective agents. Vitamin E is well-known for its intrinsic antioxidant property even though the differential effect of specific analogs of tocopherol (TP) and tocotrienol (T3) is still not ascertained. This study investigates the protective effect of T3 analogs (α-, δ-, γ−) in comparison with α-TP followed by assessing the underlying mechanisms of the cytoprotective T3 analog(s) in two xenobiotics-induced liver injury models using (1) acetaminophen (APAP)- and (2) hydrogen peroxide (H₂O₂). Both α-TP and α-T3 exerted cytoprotective effects while only lower concentration of γ-T3 was effective in inhibiting both toxicants induced injury. α-TP/α-T3 protected hepatocytes from APAP and H₂O₂-induced liver injury through arresting free radicals and inhibiting oxidative stress (inhibition of reactive oxygen species, lipid peroxidation and mitochondrial permeability transition). There was also demonstrable inhibition of the apoptotic pathway (inhibition of caspse-3 activity and overexpression of Bcl-_XL), accompanied with an induction of liver regeneration (PCNA and NF-kB). The cellular uptake of α-T3 was higher than α-TP at the same treatment dosage after 24 h. Overall, α-T3 seems to be a more potent hepatoprotective analog among the tocotrienols and α-TP at the same in vitro treatment dosage. In summary, these results suggest that α-TP/α-T3 elicit hepatoprotective effects against toxicants-induced damage mainly through activation of antioxidant responses at an early stage to prevent the exacerbation of injury.

•

Purified T3 analogs were compared for their hepatoprotective effects against two toxicants-induced liver injuries.

•

α-TP/α-T3 and lower concentration of γ-T3 exerted significant cytoprotective effects.

•

α-TP/α-T3 inhibits oxidative stress and apoptosis while induces liver regeneration.

•

α-T3 is the most potent hepatoprotective analog among T3 and α-TP at same dose.

•

α-TP/α-T3 prevented toxicants-induced injury mainly through antioxidant responses.

Direct binding of PP2A to Sprouty2 and phosphorylation changes are a prerequisite for ERK inhibition downstream of fibroblast growth factor receptor stimulation

In the context of fibroblast growth factor (FGF) signaling, Sprouty2 (Spry2) is the most profound inhibitor of the Ras/ERK pathway as compared with other Spry isoforms. An exclusive, necessary, but cryptic PXXPXR motif in the C terminus of Spry2 is revealed upon stimulation. The activation of Spry2 appears to be linked to sequences in the N-terminal half of the protein and correlated with a bandshifting seen on SDS-PAGE. The band-shifting is likely caused by changes in the phosphorylation status of key Ser and Thr residues following receptor stimulation. Dephosphorylation of at least two conserved Ser residues (Ser-112 and Ser-115) within a conserved Ser/Thr sequence is accomplished upon stimulation by a phosphatase that binds to Spry2 around residues 50-60. We show that human Spry2 co-immunoprecipitates with both the catalytic and the regulatory subunits of protein phosphatase 2A (PP2A-C and PP2A-A, respectively) in cells upon FGF receptor (FGFR) activation. PP2A-A binds directly to Spry2, but not to Spry2Delta50-60 (Delta50-60), and the activity of PP2A increases with both FGF treatment and FGFR1 overexpression. c-Cbl and PP2A-A compete for binding centered around Tyr-55 on Spry2. We show that there are at least two distinct pools of Spry2, one that binds PP2A and another that binds c-Cbl. c-Cbl binding likely targets Spry2 for ubiquitin-linked destruction, whereas the phosphatase binding and activity are necessary to dephosphorylate specific Ser/Thr residues. The resulting change in tertiary structure enables the Pro-rich motif to be revealed with subsequent binding of Grb2, a necessary step for Spry2 to act as a Ras/ERK pathway inhibitor in FGF signaling.

A Src homology 3-binding sequence on the C terminus of Sprouty2 is necessary for inhibition of the Ras/ERK pathway downstream of fibroblast growth factor receptor stimulation

Because the Sprouty (Spry) proteins were shown to be inhibitors of the mainstream Ras/ERK pathway, there has been considerable interest in ascertaining their mechanism of action especially since a possible role as tumor suppressors for these inhibitory proteins has been suggested. We compared the ability of the mammalian Spry isoforms to inhibit the Ras/ERK pathway in the context of fibroblast growth factor receptor (FGFR) signaling. Spry2 is considerably more inhibitory than Spry1 or Spry4, and this correlates with the binding to Grb2 via a C-terminal proline-rich sequence that is found exclusively on Spry2. This PXXPXR motif binds directly to the N-terminal Src homology domain 3 of Grb2, and when added onto the C terminus of Spry4 the resultant chimera inhibits the Ras/ERK pathway. The ability to inhibit neurite outgrowth in PC-12 cells correlates with the propensity of Spry isoforms and engineered constructs to inhibit the phosphorylation of ERK1/2. The PXXPXR motif is cryptic in unstimulated cells, and it is postulated that Spry2 undergoes a conformational change following FGFR stimulation, enabling the subsequent interaction with Grb2. We present evidence that Spry2 can compete with the RasGEF (guanine nucleotide exchange factor) SOS1 for binding to Grb2, resulting in the inhibition of phosphorylation of ERK1/2.

Comparison of different test models for the assessment of cytotoxicity of composite resins

This study compared the use of different test models to assess the cytotoxicity of a dental composite. The cytotoxicity of a composite polymerized using two halogen-based light-curing units (LCUs) (Max LC and Astralis) and two light-emitting diode LCUs (E-light and Freelight) served as the basis of comparison. Disk-shaped specimens (7 mm diameter, 2 mm high) were fabricated using the four different light sources. The specimens were used in several cytotoxicity test models: direct and indirect contact tests as well as an extract test with an established cell line L-929. The cells were stained with neutral red after cell-material contact for 48 h. Neutral red-stained areas (in mm2, for direct and indirect tests) and absorbance readings (for extract tests) were analysed statistically using ANOVA and the Tukey post hoc test, with P < 0.05 considered to be significantly different. Good correlation between direct and indirect contact tests (r = 0.903) was found. The extract test was the least correlated among the three tests. It was found that the E-light + Freelight-cured composite elicited cytotoxicity from the correlated studies. Uncured specimens were most detrimental to the cells in all tests. Our data demonstrated that composite cured with light-emitting diode LCUs were cytotoxic to L-929 cells. Different test models were found to give rise to different findings. Thus, a good cell-material contact method would replicate more closely the physiological situation in vivo. This in turn would give more clinically relevant results.

Tooth slice organ culture and established cell line culture models for cytotoxicity assessment of dental materials

The aim was to compare the use of different cell-material contact test methods with two different biological systems (cell line and tooth slice cultures) for cytotoxicity assessment of dental materials. Cytotoxicity of composites polymerized with two halogen-based and two light-emitting diode (LED) light-curing units (LCUs) served as the basis for comparison. Disk shaped specimens (7 x 2 mm) were fabricated using the four light sources. Composites were tested using L-929 cell line using direct/indirect/extract tests in accordance to standard protocols. Cytotoxicity was assessed using neutral red uptake. Tooth slice organ cultures were also employed to test the dental materials using direct/indirect test methods. Histomorphometric cell counting of intact odontoblasts and pulp fibroblasts and the use of tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were applied for cytotoxicity evaluation. Discrepancy in result presentation was observed in the different tests used with L-929. Sensitivity levels of the L-929 tests ranked as follows: extract test < direct contact test < indirect contact test. Tooth slice tests confirmed that L-929 direct contact test proved to be the most reliable test among the three. In conclusion, this study highlights the risk involved when relying on a single test method for cytotoxicity assessment. It would be advisable to test different culture models and then proceed using more clinically relevant biological system that stimulate the in vivo situation for confirmation.

Composite cure and pulp-cell cytotoxicity associated with LED curing lights

This study compared the cure and pulp-cell cytotoxicity of composites polymerized with light-emitting diode (LED) and halogen-based light curing units. A mini-filled resin composite (Tetric Ceram, Vivadent), two LED (E-light [EL], GC and Freelight [FL], 3M-ESPE), a conventional halogen (Max [MX], Dentsply) and a high-intensity halogen light (Astralis 10 [AS], Vivadent) were evaluated. Cure associated with the different lights was determined by measuring the top and bottom surface hardness (KHN; n = 5) of 2-mm thick specimens using a digital microhardness tester (load = 500 gf; dwell time = 15 seconds). Pulp-cell cytotoxicity was assessed using a direct contact method involving incisor tooth slices dissected from 28-day old Wistar rats maintained in Dulbecco's Modified Eagle's Medium (DMEM) and 1% agarose. The bottom surfaces of the cured composite specimens (7-mm diameter and 2-mm deep) were placed in contact with the openings of each tooth slice. After incubation in 5% CO2 atmosphere at 37 degrees C for 48 hours, the tooth slices were fixed, demineralized and processed for histological examination. Pulp fibroblasts and odontoblasts were counted histomorphometrically at 400x magnification within a 1500 microm2 area using a computerized micro-imaging system. Eighteen readings were obtained for each curing light. Data was subjected to ANOVA/Scheffe's test and Pearson's correlation at significance level 0.05 and 0.01, respectively. At the top surfaces, the cure with AS was significantly greater than the other curing lights, with MX and FL being significantly greater than EL. At the bottom surfaces, MX, AS and FL had significantly better cure than EL. Specimens cured with MX were less cytotoxic than those polymerized with other curing lights. Specimens cured with AS and EL were significantly less cytotoxic than FL. Composite cure and cytotoxicity associated with LED lights is device dependent. Composite cure was not correlated to pulp-cell cytotoxicity. The response of pulpal fibroblasts to unreacted/leached components of composites differs somewhat from odontoblasts.