Extracellular vesicles: A new paradigm in understanding, diagnosing and treating neurodegenerative disease.

Neurodegenerative disorders (NDs) are becoming one of the leading causes of disability and death across the globe due to lack of timely preventions and treatments. Concurrently, intensive research efforts are being carried out to understand the etiology of these age-dependent disorders. Extracellular vesicles (EVs)-biological nanoparticles released by cells-are gaining tremendous attention in understanding their role in pathogenesis and progression of NDs. EVs have been found to transmit pathogenic proteins of NDs between neurons. Moreover, the ability of EVs to exquisitely surmount natural biological barriers, including blood-brain barrier and in vivo safety has generated interest in exploring them as potential biomarkers and function as natural delivery vehicles of drugs to the central nervous system. However, limited knowledge of EV biogenesis, their heterogeneity and lack of adequate isolation and analysis tools have hampered their therapeutic potential. In this review, we cover the recent advances in understanding the role of EVs in neurodegeneration and address their role as biomarkers and delivery vehicles to the brain.

Clinical relevance of biomarkers, new therapeutic approaches, and role of post-translational modifications in the pathogenesis of Alzheimer's disease.

Alzheimer's disease (AD) is a neurodegenerative disorder that causes progressive loss of cognitive functions like thinking, memory, reasoning, behavioral abilities, and social skills thus affecting the ability of a person to perform normal daily functions independently. There is no definitive cure for this disease, and treatment options available for the management of the disease are not very effective as well. Based on histopathology, AD is characterized by the accumulation of insoluble deposits of amyloid beta (Aß) plaques and neurofibrillary tangles (NFTs). Although several molecular events contribute to the formation of these insoluble deposits, the aberrant post-translational modifications (PTMs) of AD-related proteins (like APP, Aß, tau, and BACE1) are also known to be involved in the onset and progression of this disease. However, early diagnosis of the disease as well as the development of effective therapeutic approaches is impeded by lack of proper clinical biomarkers. In this review, we summarized the current status and clinical relevance of biomarkers from cerebrospinal fluid (CSF), blood and extracellular vesicles involved in onset and progression of AD. Moreover, we highlight the effects of several PTMs on the AD-related proteins, and provide an insight how these modifications impact the structure and function of proteins leading to AD pathology. Finally, for disease-modifying therapeutics, novel approaches, and targets are discussed for the successful treatment and management of AD.

GAPDH controls extracellular vesicle biogenesis and enhances the therapeutic potential of EV mediated siRNA delivery to the brain.

Extracellular vesicles (EVs) are biological nanoparticles with important roles in intercellular communication, and potential as drug delivery vehicles. Here we demonstrate a role for the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in EV assembly and secretion. We observe high levels of GAPDH binding to the outer surface of EVs via a phosphatidylserine binding motif (G58), which promotes extensive EV clustering. Further studies in a Drosophila EV biogenesis model reveal that GAPDH is required for the normal generation of intraluminal vesicles in endosomal compartments, and promotes vesicle clustering. Fusion of the GAPDH-derived G58 peptide to dsRNA-binding motifs enables highly efficient loading of small interfering RNA (siRNA) onto the EV surface. Such vesicles efficiently deliver siRNA to multiple anatomical regions of the brain in a Huntington's disease mouse model after systemic injection, resulting in silencing of the huntingtin gene in different regions of the brain.

Efficiency of dual siRNA-mediated gene therapy for intervertebral disc degeneration (IVDD).

BACKGROUND CONTEXT: One of the common causes of low back pain is intervertebral disc degeneration. The pathophysiology of disc degeneration involves apoptosis of nucleus pulposes cells and degradation of extra cellular matrix (ECM). Caspase 3 plays a central role in apoptosis and the ADAMTS5 (A Disintegrin and Metalloproteinase with Thrombospondin motifs 5) gene plays a critical role in ECM degradation. Hence, we hypothesized that if one can silence these two genes, both apoptosis and ECM degradation can be prevented, thereby preventing the progression and even reverse disc degeneration. PURPOSE: The purpose of this study is to demonstrate the regenerative potential of small interfering RNA (siRNA) designed against Caspase 3 and ADAMTS5 genes in an in vitro and animal model of disc degeneration. STUDY DESIGN: In vitro study followed by in vivo study in a rabbit model. METHODS: In vitro studies were done using the human hepatocellular carcinoma (Hep G2) cell line for validating the efficacy of liposomal siRNA in controlling the expression of genes (Caspase 3 and ADAMTS5). Later, siRNA's validation was done in a rabbit annular punctured model by administering siRNA's individually (Caspase 3 and ADAMTS5) and in combination Caspase3-ADAMTS5) for assessing their synergistic effect in down regulating the gene expression in the degenerative discs. Annular punctured intervertebral discs of the rabbit were injected with siRNA formulations (single and dual) and phosphate buffer saline, one week after initial puncture. Magnetic resonance imaging (MRI) scans were done before and after siRNA treatment (1, 4 and 8 weeks) for assessing the progression of disc degeneration. The histopathology and real time polymerase chain reaction (RT-PCR) studies were done for evaluating their efficacy. We did not receive any funding for conducting the study, and we do not have a conflict of interest with any researchers or scientific groups. RESULTS: The observations made from both in vitro and in vivo studies indicate the beneficial effects of siRNA formulation in down regulating the expression of Caspase 3 and ADAMTS5 genes. The MRI and histopathological evaluation showed that the disc degeneration was progressive in phosphate buffer saline and AT5-siRNA injected discs but the discs that received Caspase 3-siRNA and dual siRNA (Cas3-AT5-siRNA) formulation showed signs of recovery and regeneration 4 and 8 weeks after injection. The efficacy of siRNA designed against Cas3 and AT5 was also assessed in both in vitro and in vivo experiments by using RT-PCR analysis and the results showed downregulation of Caspase 3 gene in Caspase 3-siRNA group, but there was no significant downregulation of ADAMTS5 gene in ADAMTS5-siRNA group (ie, indicated by fold change). Synergistic effect was observed in the group that received dual siRNA (Cas3-AT5 siRNA) formulation. CONCLUSIONS: This experiment suggests that intervention by siRNA treatment significantly reduced the extent of apoptosis in the discs. CLINICAL SIGNIFICANCE: Delivery of siRNA directly into spinal discs has a potential in treating disc degeneration nonsurgically.

Engineered fusion protein-loaded gold nanocarriers for targeted co-delivery of doxorubicin and erbB2-siRNA in human epidermal growth factor receptor-2+ ovarian cancer.

Designed recombinant proteins comprising functional domains offer selective targeting of cancer cells for the efficient delivery of therapeutic agents. The efficacy of these carriers can be further enhanced by conjugating engineered proteins to nanoparticle surfaces. However, recombinant protein-loaded nanoparticle-based drug delivery systems are not well addressed for ovarian cancer therapy. In the present study, using a combinatorial approach, we designed and fabricated a drug delivery system by combining gold nanoparticles (AuNPs) with an engineered bi-functional recombinant fusion protein TRAF(C) (TR), loaded with an anticancer drug, namely doxorubicin (DX), and erbB2-siRNA (si), to mediate target specific delivery into SK-OV-3, a model human ovarian cancer cell line over expressing HER2 receptors (i.e. human epidermal growth factor receptor-2). The nanoparticle-based targeted drug delivery system, designated as TDDS (Au-TR-DX-si), was found to be stable and homogenous as revealed by physicochemical and biochemical studies in vitro. In addition, TDDS was functional upon evaluation in vivo. Intraperitoneal administration of TDDS at 2.5 mg kg-1 of DX and 0.25 mg kg-1 of erbB2 siRNA into SK-OV-3 xenograft nude mice, revealed target specific uptake and consequent gene silencing resulting in significant tumor suppression. We attribute these results to specific co-delivery of erbB2 siRNA and DX mediated by TDDS into SK-OV-3 cells via HER2 receptors. Additionally, the biodistribution of TDDS, as quantitated by ICP-OES, confirmed tumor-specific accumulation of AuNPs primarily in tumor tissues, which firmly establishes the efficacy of the nanomedicine-based combinatorial approach for the treatment of ovarian cancer in a non-toxic manner. Based on these findings, we strongly believe that the nanomedicine-based combinatorial approach can be developed as a universal strategy for treatment of HER2+ ovarian cancers.

A designed recombinant fusion protein for targeted delivery of siRNA to the mouse brain.

RNA interference represents a novel therapeutic approach to modulate several neurodegenerative disease-related genes. However, exogenous delivery of siRNA restricts their transport into different tissues and specifically into the brain mainly due to its large size and the presence of the blood-brain barrier (BBB). To overcome these challenges, we developed here a strategy wherein a peptide known to target specific gangliosides was fused to a double-stranded RNA binding protein to deliver siRNA to the brain parenchyma. The designed fusion protein designated as TARBP-BTP consists of a double-stranded RNA-binding domain (dsRBD) of human Trans Activation response element (TAR) RNA Binding Protein (TARBP2) fused to a brain targeting peptide that binds to monosialoganglioside GM1. Conformation-specific binding of TARBP2 domain to siRNA led to the formation of homogenous serum-stable complex with targeting potential. Further, uptake of the complex in Neuro-2a, IMR32 and HepG2 cells analyzed by confocal microscopy and fluorescence activated cell sorting, revealed selective requirement of GM1 for entry. Remarkably, systemic delivery of the fluorescently labeled complex (TARBP-BTP:siRNA) in ΑßPP-PS1 mouse model of Alzheimer's disease (AD) led to distinctive localization in the cerebral hemisphere. Further, the delivery of siRNA mediated by TARBP-BTP led to significant knockdown of BACE1 in the brain, in both ΑßPP-PS1 mice and wild type C57BL/6. The study establishes the growing importance of fusion proteins in delivering therapeutic siRNA to brain tissues.

Conformation-dependent binding and tumor-targeted delivery of siRNA by a designed TRBP2: Affibody fusion protein.

Efficiency of systemically delivered siRNA in gene silencing is compromised due to lack of target-specific delivery and rapid clearance of siRNA by in vivo elimination pathways. We designed a fusion protein consisting of a dsRNA binding domain of transactivation response RNA binding protein (TRBP2) fused to ErbB2 binding affibody (AF) for target specific delivery of siRNA. Designated as TRAF, the fusion protein is stable and binds efficiently and specifically to siRNA, forming homogenous non-aggregated and nuclease-resistant particles that efficiently and selectively transport siRNA into HER-2 overexpressing cancer cells and tissues. Administration of siRNA by TRAF into cells resulted in significant silencing of chosen genes involved in cell proliferation viz. AURKB and ErbB2. Noticeably, intravenous administration of TRAF:siRNA against these genes resulted in remarkable tumor suppression in the SK-OV-3 xenograft mouse model. Our results establish the potential of engineered proteins for specific and systemic delivery of siRNA for cancer therapy. FROM THE CLINICAL EDITOR: The use of siRNA in one of many novel treatments in cancer therapy. However, a major challenge for using siRNA is the lack of specificity and rapid RNA clearance. In this article, the authors designed a tumor targeting fusion protein, which can deliver siRNA specifically. In the experimental xenograft model, it was shown that intravenous administration of this resulted in significant tumor suppression. The results seem to hold promise in future clinical studies.

Systemic delivery of stable siRNA-encapsulating lipid vesicles: optimization, biodistribution, and tumor suppression.

Lipid-based nanoparticles are considered as promising candidates for delivering siRNA into the cytoplasm of targeted cells. However, in vivo efficiency of these nanoparticles is critically dependent on formulation strategies of lipid-siRNA complexes. Adsorption of serum proteins to lipid-siRNA complexes and its charge determine siRNA degradation and serum half-life, thus significantly altering the bioavailability of siRNA. To address these challenges, we developed a formulation comprising dihydroxy cationic lipid, N,N-di-n-hexadecyl-N,N-dihydroxyethylammonium chloride (DHDEAC), cholesterol, and varying concentrations of 1,2-distearoryl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol-2000)] (DSPE-PEG 2000). Using an ethanol dilution method, addition of these lipids to siRNA solution leads to formation of stable and homogeneous population of siRNA-encapsulated vesicles (SEVs). Biodistribution of these SEVs, containing 5 mol % of DSPE-PEG 2000 in xenograft mice, as monitored by live animal imaging and fluorescence microscopy, revealed selective accumulation in the tumor. Remarkably, four intravenous injections of the modified vesicles with equimolar amounts of siRNA targeting ErbB2 and AURKB genes led to significant gene silencing and concomitant tumor suppression in the SK-OV-3 xenograft mouse model. Safety parameters as evaluated by various markers of hepatocellular injury indicated the nontoxic nature of this formulation. These results highlight improved pharmacokinetics and effective in vivo delivery of siRNA by DHDEAC-based vesicles.