APOE2 mitigates disease-related phenotypes in an isogenic hiPSC-based model of Alzheimer's disease

Engineered Gold and Silica Nanoparticle-Incorporated Hydrogel Scaffolds for Human Stem Cell-Derived Cardiac Tissue Engineering

Electrically conductive biomaterials and nanomaterials have demonstrated great potential in the development of functional and mature cardiac tissues. In particular, gold nanomaterials have emerged as promising candidates due to their biocompatibility and ease of fabrication for cardiac tissue engineering utilizing rat- or stem cell-derived cardiomyocytes (CMs). However, despite significant advancements, it is still not clear whether the enhancement in cardiac tissue function is primarily due to the electroconductivity features of gold nanoparticles or the structural changes of the scaffold resulting from the addition of these nanoparticles. To address this question, we developed nanoengineered hydrogel scaffolds comprising gelatin methacrylate (GelMA) embedded with either electrically conductive gold nanorods (GNRs) or nonconductive silica nanoparticles (SNPs). This enabled us to simultaneously assess the roles of electrically conductive and nonconductive nanomaterials in the functionality and fate of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Our studies revealed that both GNR- and SNP-incorporated hydrogel scaffolds exhibited excellent biocompatibility and similar cardiac cell attachment. Although the expression of sarcomere alpha-actinin did not significantly differ among the conditions, a more organized sarcomere structure was observed within the GNR-embedded hydrogels compared to the nonconductive nanoengineered scaffolds. Furthermore, electrical coupling was notably improved in GNR-embedded scaffolds, as evidenced by the synchronous calcium flux and enhanced calcium transient intensity. While we did not observe a significant difference in the gene expression profile of human cardiac tissues formed on the conductive GNR- and nonconductive SNP-incorporated hydrogels, we noticed marginal improvements in the expression of some calcium and structural genes in the nanomaterial-embedded hydrogel groups as compared to the control condition. Given that the cardiac tissues formed atop the nonconductive SNP-based scaffolds (used as the control for conductivity) also displayed similar levels of gene expression as compared to the conductive hydrogels, it suggests that the electrical conductivity of nanomaterials (i.e., GNRs) may not be the sole factor influencing the function and fate of hiPSC-derived cardiac tissues when cells are cultured atop the scaffolds. Overall, our findings provide additional insights into the role of electrically conductive gold nanoparticles in regulating the functionalities of hiPSC-CMs.

PINE-TREE enables highly efficient genetic modification of human cell lines

Prime editing technologies enable precise genome editing without the caveats of CRISPR nuclease-based methods. Nonetheless, current approaches to identify and isolate prime-edited cell populations are inefficient. Here, we established a fluorescence-based system, prime-induced nucleotide engineering using a transient reporter for editing enrichment (PINE-TREE), for real-time enrichment of prime-edited cell populations. We demonstrated the broad utility of PINE-TREE for highly efficient introduction of substitutions, insertions, and deletions at various genomic loci. Finally, we employ PINE-TREE to rapidly and efficiently generate clonal isogenic human pluripotent stem cell lines, a cell type recalcitrant to genome editing.

APOE deficiency impacts neural differentiation and cholesterol biosynthesis in human iPSC-derived cerebral organoids

BACKGROUND

The apolipoprotein E (APOE) gene is the strongest genetic risk factor for Alzheimer's disease (AD); however, how it modulates brain homeostasis is not clear. The apoE protein is a major lipid carrier in the brain transporting lipids such as cholesterol among different brain cell types.

METHODS

We generated three-dimensional (3-D) cerebral organoids from human parental iPSC lines and its isogenic APOE-deficient (APOE-/-) iPSC line. To elucidate the cell-type-specific effects of APOE deficiency in the cerebral organoids, we performed scRNA-seq in the parental and APOE-/- cerebral organoids at Day 90.

RESULTS

We show that APOE deficiency in human iPSC-derived cerebral organoids impacts brain lipid homeostasis by modulating multiple cellular and molecular pathways. Molecular profiling through single-cell RNA sequencing revealed that APOE deficiency leads to changes in cellular composition of isogenic cerebral organoids likely by modulating the eukaryotic initiation factor 2 (EIF2) signaling pathway as these events were alleviated by the treatment of an integrated stress response inhibitor (ISRIB). APOE deletion also leads to activation of the Wnt/β-catenin signaling pathway with concomitant decrease of secreted frizzled-related protein 1 (SFRP1) expression in glia cells. Importantly, the critical role of apoE in cell-type-specific lipid homeostasis was observed upon APOE deletion in cerebral organoids with a specific upregulation of cholesterol biosynthesis in excitatory neurons and excessive lipid accumulation in astrocytes. Relevant to human AD, APOE4 cerebral organoids show altered neurogenesis and cholesterol metabolism compared to those with APOE3.

CONCLUSIONS

Our work demonstrates critical roles of apoE in brain homeostasis and offers critical insights into the APOE4-related pathogenic mechanisms.

Relationship of Apolipoprotein E with Alzheimer's Disease and Other Neurological Disorders: An Updated Review

Alzheimer's disease (AD) and other neurodegenerative diseases, for which there is no effective cure, cause great social burden. Apolipoprotein E (APOE) is an important lipid transporter, which has been shown to have a close relationship with AD and other neurological disorders in an increasing number of studies, suggesting its potential as a therapeutic target. In this review, we summarize the recent advances in clinical and basic research on the role of APOE in the pathogenesis of multiple neurological diseases, with an emphasis on the new associations between APOE and AD, and between APOE and depression. The progress of APOE research in Parkinson's disease (PD) and some other neurological diseases is briefly discussed.

Endotype reversal as a novel strategy for screening drugs targeting familial Alzheimer's disease

While amyloid-β (Aβ) plaques are considered a hallmark of Alzheimer's disease, clinical trials focused on targeting gamma secretase, an enzyme involved in aberrant Aβ peptide production, have not led to amelioration of AD symptoms or synaptic dysregulation. Screening strategies based on mechanistic, multi-omics approaches that go beyond pathological readouts can aid in the evaluation of therapeutics. Using early-onset Alzheimer's (EOFAD) disease patient lineage PSEN1^A246E iPSC-derived neurons, we performed RNA-seq to characterize AD-associated endotypes, which are in turn used as a screening evaluation metric for two gamma secretase drugs, the inhibitor Semagacestat and the modulator BPN-15606. We demonstrate that drug treatment partially restores the neuronal state while concomitantly inhibiting cell cycle re-entry and dedifferentiation endotypes to different degrees depending on the mechanism of gamma secretase engagement. Our endotype-centric screening approach offers a new paradigm by which candidate AD therapeutics can be evaluated for their overall ability to reverse disease endotypes.

A microcarrier-based protocol for scalable generation and purification of human induced pluripotent stem cell-derived neurons and astrocytes

Here, we describe a protocol for a microcarrier (MC)-based, large-scale generation and cryopreservation of human-induced pluripotent stem cell (hiPSC)-derived neurons and astrocytes. We also detail steps to isolate these populations with a high degree of purity. Finally, we describe how to cryopreserve these cell types while maintaining high levels of viability and preserving cellular function post-thaw. For complete details on the use and execution of this protocol, please refer to Brookhouser et al. (2021).

Neuronal hyperexcitability in Alzheimer's disease: what are the drivers behind this aberrant phenotype?

Alzheimer's disease (AD) is a progressive neurodegenerative disorder leading to loss of cognitive abilities and ultimately, death. With no cure available, limited treatments mostly focus on symptom management. Identifying early changes in the disease course may provide new therapeutic targets to halt or reverse disease progression. Clinical studies have shown that cortical and hippocampal hyperactivity are a feature shared by patients in the early stages of disease, progressing to hypoactivity during later stages of neurodegeneration. The exact mechanisms causing neuronal excitability changes are not fully characterized; however, animal and cell models have provided insights into some of the factors involved in this phenotype. In this review, we summarize the evidence for neuronal excitability changes over the course of AD onset and progression and the molecular mechanisms underpinning these differences. Specifically, we discuss contributors to aberrant neuronal excitability, including abnormal levels of intracellular Ca²⁺ and glutamate, pathological amyloid β (Aβ) and tau, genetic risk factors, including APOE, and impaired inhibitory interneuron and glial function. In light of recent research indicating hyperexcitability could be a predictive marker of cognitive dysfunction, we further argue that the hyperexcitability phenotype could be leveraged to improve the diagnosis and treatment of AD, and present potential targets for future AD treatment development.

The Emergence of Model Systems to Investigate the Link Between Traumatic Brain Injury and Alzheimer’s Disease

Numerous epidemiological studies have demonstrated that individuals who have sustained a traumatic brain injury (TBI) have an elevated risk for developing Alzheimer’s disease and Alzheimer’s-related dementias (AD/ADRD). Despite these connections, the underlying mechanisms by which TBI induces AD-related pathology, neuronal dysfunction, and cognitive decline have yet to be elucidated. In this review, we will discuss the various in vivo and in vitro models that are being employed to provide more definite mechanistic relationships between TBI-induced mechanical injury and AD-related phenotypes. In particular, we will highlight the strengths and weaknesses of each of these model systems as it relates to advancing the understanding of the mechanisms that lead to TBI-induced AD onset and progression as well as providing platforms to evaluate potential therapies. Finally, we will discuss how emerging methods including the use of human induced pluripotent stem cell (hiPSC)-derived cultures and genome engineering technologies can be employed to generate better models of TBI-induced AD.

Calcium Ions Aggravate Alzheimer's Disease Through the Aberrant Activation of Neuronal Networks, Leading to Synaptic and Cognitive Deficits

Alzheimer’s disease (AD) is a neurodegenerative disease that is characterized by the production and deposition of β-amyloid protein (Aβ) and hyperphosphorylated tau, leading to the formation of β-amyloid plaques (APs) and neurofibrillary tangles (NFTs). Although calcium ions (Ca²⁺) promote the formation of APs and NFTs, no systematic review of the mechanisms by which Ca²⁺ affects the development and progression of AD has been published. Therefore, the current review aimed to fill the gaps between elevated Ca²⁺ levels and the pathogenesis of AD. Specifically, we mainly focus on the molecular mechanisms by which Ca²⁺ affects the neuronal networks of neuroinflammation, neuronal injury, neurogenesis, neurotoxicity, neuroprotection, and autophagy. Furthermore, the roles of Ca²⁺ transporters located in the cell membrane, endoplasmic reticulum (ER), mitochondria and lysosome in mediating the effects of Ca²⁺ on activating neuronal networks that ultimately contribute to the development and progression of AD are discussed. Finally, the drug candidates derived from herbs used as food or seasoning in Chinese daily life are summarized to provide a theoretical basis for improving the clinical treatment of AD.