Analysis of the trafficking system in blood-brain barrier models by high content screening microscopy

Efficient systemic CNS delivery of a therapeutic antisense oligonucleotide with a blood-brain barrier-penetrating ApoE-derived peptide

Antisense oligonucleotide (ASO) has emerged as a promising therapeutic approach for treating central nervous system (CNS) disorders by modulating gene expression with high selectivity and specificity. However, the poor permeability of ASO across the blood-brain barrier (BBB) diminishes its therapeutic success. Here, we designed and synthesized a series of BBB-penetrating peptides (BPP) derived from either the receptor-binding domain of apolipoprotein E (ApoE) or a transferrin receptor-binding peptide (THR). The BPPs were conjugated to phosphorodiamidate morpholino oligomers (PMO) that are chemically analogous to the 2'-O-(2-methoxyethyl) (MOE)-modified ASO approved by the FDA for treating spinal muscular atrophy (SMA). The BPP-PMO conjugates significantly increased the level of full-length SMN2 in the patient-derived SMA fibroblasts in a concentration-dependent manner with minimal to no toxicity. Furthermore, the systemic administration of the most potent BPP-PMO conjugates significantly increased the expression of full-length SMN2 in the brain and spinal cord of SMN2 transgenic adult mice. Notably, BPP8-PMO conjugate showed a 1.25-fold increase in the expression of full-length functional SMN2 in the brain. Fluorescence imaging studies confirmed that 78% of the fluorescently (Cy7)-labelled BPP8-PMO reached brain parenchyma, with 11% uptake in neuronal cells. Additionally, the BPP-PMO conjugates containing retro-inverso (RI) D-BPPs were found to possess extended half-lives compared to their L-counterparts, indicating increased stability against protease degradation while preserving the bioactivity. This delivery platform based on BPP enhances the CNS bioavailability of PMO targeting the SMN2 gene, paving the way for the development of systemically administered neurotherapeutics for CNS disorders.

Cholinergic Neuron Targeting Nanosystem Delivering Hybrid Peptide for Combinatorial Mitochondrial Therapy in Alzheimer's Disease

Mitochondrial dysfunction in neurons has recently become a promising therapeutic target for Alzheimer's disease (AD). Regulation of dysfunctional mitochondria through multiple pathways rather than antioxidation monotherapy indicates synergistic therapeutic effects. Therefore, we developed a multifunctional hybrid peptide HNSS composed of antioxidant peptide SS31 and neuroprotective peptide S14G-Humanin. However, suitable peptide delivery systems with excellent loading capacity and effective at-site delivery are still absent. Herein, the nanoparticles made of citraconylation-modified poly(ethylene glycol)-poly(trimethylene carbonate) polymer (PEG-PTMC(Cit)) exhibited desirable loading of HNSS peptide through electrostatic interactions. Meanwhile, based on fibroblast growth factor receptor 1(FGFR1) overexpression in both the blood-brain barrier and cholinergic neuron, an FGFR1 ligand-FGL peptide was modified on the nanosystem (FGL-NP(Cit)/HNSS) to achieve 4.8-fold enhanced accumulation in brain with preferred distribution into cholinergic neurons in the diseased region. The acid-sensitive property of the nanosystem facilitated lysosomal escape and intracellular drug release by charge switching, resulting in HNSS enrichment in mitochondria through directing of the SS31 part. FGL-NP(Cit)/HNSS effectively rescued mitochondria dysfunction via the PGC-1α and STAT3 pathways, inhibited Aβ deposition and tau hyperphosphorylation, and ameliorated memory defects and cholinergic neuronal damage in 3xTg-AD mice. The work provides a potential platform for targeted cationic peptide delivery, harboring utility for peptide therapy in other neurodegenerative diseases.

Vesicular Transport Machinery in Brain Endothelial Cells: What We Know and What We Do not

The vesicular transport machinery regulates numerous essential functions in cells such as cell polarity, signaling pathways, and the transport of receptors and their cargoes. From a pharmaceutical perspective, vesicular transport offers avenues to facilitate the uptake of therapeutic agents into cells and across cellular barriers. In order to improve receptor-mediated transcytosis of biologics across the blood-brain barrier and into the diseased brain, a detailed understanding of intracellular transport mechanisms is essential. The vesicular transport machinery is a highly complex network and involves an array of protein complexes, cytosolic adaptor proteins, and the subcellular structures of the endo-lysosomal system. The endo-lysosomal system includes several types of vesicular entities such as early, late, and recycling endosomes, exosomes, ectosomes, retromer-coated vesicles, lysosomes, trans-endothelial channels, and tubules. While extensive research has been done on the trafficking system in many cell types, little is known about vesicular trafficking in brain endothelial cells. Consequently, assumptions on the transport system in endothelial cells are based on findings in polarised epithelial cells, although recent studies have highlighted differences in the endothelial system. This review highlights aspects of the vesicular trafficking machinery in brain endothelial cells, including recent findings, limitations, and opportunities for further studies.

Modeling Nanocarrier Transport across a 3D In Vitro Human Blood-Brain-Barrier Microvasculature

Polymer nanoparticles (NPs), due to their small size and surface functionalization potential have demonstrated effective drug transport across the blood-brain-barrier (BBB). Currently, the lack of in vitro BBB models that closely recapitulate complex human brain microenvironments contributes to high failure rates of neuropharmaceutical clinical trials. In this work, a previously established microfluidic 3D in vitro human BBB model, formed by the self-assembly of human-induced pluripotent stem cell-derived endothelial cells, primary brain pericytes, and astrocytes in triculture within a 3D fibrin hydrogel is exploited to quantify polymer NP permeability, as a function of size and surface chemistry. Microvasculature are perfused with commercially available 100-400 nm fluorescent polystyrene (PS) NPs, and newly synthesized 100 nm rhodamine-labeled polyurethane (PU) NPs. Confocal images are taken at different timepoints and computationally analyzed to quantify fluorescence intensity inside/outside the microvasculature, to determine NP spatial distribution and permeability in 3D. Results show similar permeability of PS and PU NPs, which increases after surface-functionalization with brain-associated ligand holo-transferrin. Compared to conventional transwell models, the method enables rapid analysis of NP permeability in a physiologically relevant human BBB set-up. Therefore, this work demonstrates a new methodology to preclinically assess NP ability to cross the human BBB.

Modeling Nanocarrier Transport across a 3D In Vitro Human Blood-Brain-Barrier Microvasculature

Polymer nanoparticles (NPs), due to their small size and surface functionalization potential have demonstrated effective drug transport across the blood-brain-barrier (BBB). Currently, the lack of in vitro BBB models that closely recapitulate complex human brain microenvironments contributes to high failure rates of neuropharmaceutical clinical trials. In this work, a previously established microfluidic 3D in vitro human BBB model, formed by the self-assembly of human-induced pluripotent stem cell-derived endothelial cells, primary brain pericytes, and astrocytes in triculture within a 3D fibrin hydrogel is exploited to quantify polymer NP permeability, as a function of size and surface chemistry. Microvasculature are perfused with commercially available 100-400 nm fluorescent polystyrene (PS) NPs, and newly synthesized 100 nm rhodamine-labeled polyurethane (PU) NPs. Confocal images are taken at different timepoints and computationally analyzed to quantify fluorescence intensity inside/outside the microvasculature, to determine NP spatial distribution and permeability in 3D. Results show similar permeability of PS and PU NPs, which increases after surface-functionalization with brain-associated ligand holo-transferrin. Compared to conventional transwell models, the method enables rapid analysis of NP permeability in a physiologically relevant human BBB set-up. Therefore, this work demonstrates a new methodology to preclinically assess NP ability to cross the human BBB.

Novel circular RNAs expressed in brain microvascular endothelial cells after oxygen-glucose deprivation/recovery

Circular RNAs (circRNAs) are generated by head-to-tail splicing and are ubiquitously expressed in all multicellular organisms. Their important biological functions are increasingly recognized. Cerebral ischemia reperfusion injury-induced brain microvascular endothelial cell dysfunction is an initial stage of blood-brain barrier disruption. The expression profile and potential function of circRNAs in brain microvascular endothelial cells is unknown. Rat brain microvascular endothelial cells were extracted and cultured in glucose-free medium for 4 hours with 5% CO₂ and 95% N₂, and the medium was then replaced with complete growth medium for 6 hours. The RNA in these cells was then extracted. The circRNA was identified by Find_circ and CIRI2 software. Functional and pathway enrichment analysis of genes that were common to differentially expressed mRNAs and circRNA host genes was performed by the Database for Annotation, Visualization and Integrated Discovery Functional Annotation Tool. Miranda software was used to predict microRNAs that were potentially sponged by circRNAs. Furthermore, cytoscape depicted the circR-NA-microRNA interaction network. The results showed that there were 1288 circRNAs in normal and oxygen-glucose deprived/recovered primary brain microvascular endothelial cells. There are 211 upregulated and 326 downregulated differentially expressed circRNAs. The host genes of these differentially expressed circRNAs overlapped with those of differentially expressed mRNAs. The shared genes were further studied by functional enrichment analyses, which revealed that circRNAs may contribute to calcium ion function and the cyclic guanosine 3′,5′-monophosphate (CAMP) dependent protein kinase (PKα) signaling pathway. Next, quantitative reverse transcription polymerase chain reaction assays were performed to detect circRNA levels transcribed from the overlapping host genes. Eight out of the ten circRNAs with the highest fold-change identified by sequencing were successfully verified. Subsequently, the circRNA-microRNA interaction networks of these eight circRNAs were explored by bioinformatic analysis. These results demonstrate that altered circRNAs may be important in the pathogenesis of cerebral ischemia reperfusion injury and consequently may also be potential therapeutic targets for cerebral ischemia diseases. All animal experiments were approved by the Chongqing Medical University Committee on Animal Research, China (approval No. CQMU20180086) on March 22, 2018.