Multiplexed kit based on Luminex technology and achievements in synthetic biology discriminates Zika, chikungunya, and dengue viruses in mosquitoes.

BACKGROUND: The global expansion of dengue (DENV), chikungunya (CHIKV), and Zika viruses (ZIKV) is having a serious impact on public health. Because these arboviruses are transmitted by the same mosquito species and co-circulate in the same area, a sensitive diagnostic assay that detects them together, with discrimination, is needed. METHODS: We present here a diagnostics panel based on reverse transcription-PCR amplification of viral RNA and an xMap Luminex architecture involving direct hybridization of PCRamplicons and virus-specific probes. Two DNA innovations ("artificially expanded genetic information systems", AEGIS, and "self-avoiding molecular recognition systems", SAMRS) increase the hybridization sensitivity on Luminex microspheres and PCR specificity of the multiplex assay compared to the standard approach (standard nucleotides). RESULTS: The diagnostics panel detects, if they are present, these viruses with a resolution of 20 genome equivalents (DENV1), or 10 (DENV3-4, CHIKV) and 80 (DENV2, ZIKV) genome equivalents per assay. It identifies ZIKV, CHIKV and DENV RNAs in a single infected mosquito, in mosquito pools comprised of 5 to 50 individuals, and mosquito saliva (ZIKV, CHIKV, and DENV2). Infected mosquitoes and saliva were also collected on a cationic surface (Q-paper), which binds mosquito and viral nucleic acids electrostatically. All samples from infected mosquitoes displayed only target-specific signals; signals from non-infected samples were at background levels. CONCLUSIONS: Our results provide an efficient and multiplex tool that may be used for surveillance of emerging mosquito-borne pathogens which aids targeted mosquito control in areas at high risk for transmission.

Optimization of cationic (Q)-paper for detection of arboviruses in infected mosquitoes.

Previously (Glushakova et al. 2017), a cellulose-based cationic (Q) paper derivatized with quaternary ammonium groups was shown to be a convenient platform to collect, preserve, and store nucleic acids (NAs) derived from mosquito vectors infected with pathogens for surveillance. NAs bind electrostatically to Q-paper, but the quantity of NA bound depends on the paper's binding capacity. To optimize the original technology for mosquito surveillance, factors that affected NA absorbance on Q-paper were evaluated. Sixteen variations of Q-paper were prepared with modifications of the derivatizing reagents and derivatization temperature. The binding capacities of these variations were determined first with 1,3,5-benzenetricarboxylic (BTCA), then viral RNA (purified or in infected mosquito samples) was used for validation. For this, samples with Zika (ZIKV) and chikungunya (CHIKV) RNA or virus-infected Aedes aegypti mosquito bodies were applied to sixteen Q-paper variants. Washing the paper samples with water versus elution with aqueous salt (1 M) gave samples that were analyzed for viral RNA by a PCR-based direct Luminex hybridization assay. The comparison ranked the Q-paper binding capacities from the lowest to the highest. The Q-paper with the highest RNA binding capability was further validated with ZIKV- and CHIKV-infected mosquito saliva.

Detection of chikungunya viral RNA in mosquito bodies on cationic (Q) paper based on innovations in synthetic biology.

Chikungunya virus (CHIKV) represents a growing and global concern for public health that needs inexpensive and convenient methods to collect mosquitoes as potential carriers so that they can be preserved, stored and transported for later and/or remote analysis. Reported here is a cellulose-based paper, derivatized with quaternary ammonium groups ("Q-paper") that meets these needs. In a series of tests, infected mosquito bodies were squashed directly on Q-paper. Aqueous ammonia was then added on the mosquito bodies to release viral RNA that adsorbed on the cationic surface via electrostatic interactions. The samples were then stored (frozen) or transported. For analysis, the CHIKV nucleic acids were eluted from the Q-paper and PCR amplified in a workflow, previously developed, that also exploited two nucleic acid innovations, ("artificially expanded genetic information systems", AEGIS, and "self-avoiding molecular recognition systems", SAMRS). The amplicons were then analyzed by a Luminex hybridization assay. This procedure detected CHIKV RNA, if present, in each infected mosquito sample, but not in non-infected counterparts or ddH2O samples washes, with testing one week or ten months after sample collection.

Standard and AEGIS nicking molecular beacons detect amplicons from the Middle East respiratory syndrome coronavirus.

This paper combines two advances to detect MERS-CoV, the causative agent of Middle East Respiratory Syndrome, that have emerged over the past few years from the new field of "synthetic biology". Both are based on an older concept, where molecular beacons are used as the downstream detection of viral RNA in biological mixtures followed by reverse transcription PCR amplification. The first advance exploits the artificially expanded genetic information systems (AEGIS). AEGIS adds nucleotides to the four found in standard DNA and RNA (xNA); AEGIS nucleotides pair orthogonally to the A:T and G:C pairs. Placing AEGIS components in the stems of molecular beacons is shown to lower noise by preventing unwanted stem invasion by adventitious natural xNA. This should improve the signal-to-noise ratio of molecular beacons operating in complex biological mixtures. The second advance introduces a nicking enzyme that allows a single target molecule to activate more than one beacon, allowing "signal amplification". Combining these technologies in primers with components of a self-avoiding molecular recognition system (SAMRS), we detect 50 copies of MERS-CoV RNA in a multiplexed respiratory virus panel by generating fluorescence signal visible to human eye and/or camera.

Detecting respiratory viral RNA using expanded genetic alphabets and self-avoiding DNA.

Nucleic acid (NA)-targeted tests detect and quantify viral DNA and RNA (collectively xNA) to support epidemiological surveillance and, in individual patients, to guide therapy. They commonly use polymerase chain reaction (PCR) and reverse transcription PCR. Although these all have rapid turnaround, they are expensive to run. Multiplexing would allow their cost to be spread over multiple targets, but often only with lower sensitivity and accuracy, noise, false positives, and false negatives; these arise by interactions between the multiple nucleic acid primers and probes in a multiplexed kit. Here we offer a multiplexed assay for a panel of respiratory viruses that mitigates these problems by combining several nucleic acid analogs from the emerging field of synthetic biology: (i) self-avoiding molecular recognition systems (SAMRSs), which facilitate multiplexing, and (ii) artificially expanded genetic information systems (AEGISs), which enable low-noise PCR. These are supplemented by "transliteration" technology, which converts standard nucleotides in a target to AEGIS nucleotides in a product, improving hybridization. The combination supports a multiplexed Luminex-based respiratory panel that potentially differentiates influenza viruses A and B, respiratory syncytial virus, severe acute respiratory syndrome coronavirus (SARS), and Middle East respiratory syndrome (MERS) coronavirus, detecting as few as 10 MERS virions in a 20-µl sample.

High-throughput multiplexed xMAP Luminex array panel for detection of twenty two medically important mosquito-borne arboviruses based on innovations in synthetic biology.

Mosquito-borne arboviruses are emerging world-wide as important human and animal pathogens. This makes assays for their accurate and rapid identification essential for public health, epidemiological, ecological studies. Over the past decade, many mono- and multiplexed assays targeting arboviruses nucleic acids have been reported. None has become established for the routine identification of multiple viruses in a "single tube" setting. With increasing multiplexing, the detection of viral RNAs is complicated by noise, false positives and negatives. In this study, an assay was developed that avoids these problems by combining two new kinds of nucleic acids emerging from the field of synthetic biology. The first is a "self-avoiding molecular recognition system" (SAMRS), which enables high levels of multiplexing. The second is an "artificially expanded genetic information system" (AEGIS), which enables clean PCR amplification in nested PCR formats. A conversion technology was used to place AEGIS component into amplicon, improving their efficiency of hybridization on Luminex beads. When Luminex "liquid microarrays" are exploited for downstream detection, this combination supports single-tube PCR amplification assays that can identify 22 mosquito-borne RNA viruses from the genera Flavivirus, Alphavirus, Orthobunyavirus. The assay differentiates between closely-related viruses, as dengue, West Nile, Japanese encephalitis, and the California serological group. The performance and the sensitivity of the assay were evaluated with dengue viruses and infected mosquitoes; as few as 6-10 dengue virions can be detected in a single mosquito.

Conversion strategy using an expanded genetic alphabet to assay nucleic acids.

Methods to detect DNA and RNA (collectively xNA) are easily plagued by noise, false positives, and false negatives, especially with increasing levels of multiplexing in complex assay mixtures. Here, we describe assay architectures that mitigate these problems by converting standard xNA analyte sequences into sequences that incorporate nonstandard nucleotides (Z and P). Z and P are extra DNA building blocks that form tight nonstandard base pairs without cross-binding to natural oligonucleotides containing G, A, C, and T (GACT). The resulting improvements are assessed in an assay that inverts the standard Luminex xTAG architecture, placing a biotin on a primer (rather than on a triphosphate). This primer is extended on the target to create a standard GACT extension product that is captured by a CTGA oligonucleotide attached to a Luminex bead. By using conversion, a polymerase incorporates dZTP opposite template dG in the absence of dCTP. This creates a Z-containing extension product that is captured by a bead-bound oligonucleotide containing P, which binds selectively to Z. The assay with conversion produces higher signals than the assay without conversion, possibly because the Z/P pair is stronger than the C/G pair. These architectures improve the ability of the Luminex instruments to detect xNA analytes, producing higher signals without the possibility of competition from any natural oligonucleotides, even in complex biological samples.

Increased superoxide accumulation in pyruvate dehydrogenase complex deficient fibroblasts.

The pyruvate dehydrogenase complex (PDC) oxidizes pyruvate to acetyl CoA and is critically important in maintaining normal cellular energy homeostasis. Loss-of-function mutations in PDC give rise to congenital lactic acidosis and to progressive cellular energy failure. However, the subsequent biochemical consequences of PDC deficiency that may contribute to the clinical manifestations of the disorder are poorly understood. We postulated that altered flux through PDC would disrupt mitochondrial electron transport, resulting in oxidative stress. Compared to cells from 4 healthy subjects, primary cultures of skin fibroblasts from 9 patients with variable mutations in the gene encoding the alpha subunit (E1α) of pyruvate dehydrogenase (PDA1) demonstrated reduced growth and viability. Superoxide (O(2)(.-)) from the Qo site of complex III of the electron transport chain accumulated in these cells and was associated with decreased activity of manganese superoxide dismutase. The expression of uncoupling protein 2 was also decreased in patient cells, but there were no significant changes in the expression of cellular markers of protein or DNA oxidative damage. The expression of hypoxia transcription factor 1 alpha (HIF1α) also increased in PDC deficient fibroblasts. We conclude that PDC deficiency is associated with an increase in O(2)(.-) accumulation coupled to a decrease in mechanisms responsible for its removal. Increased HIF1α expression may contribute to the increase in glycolytic flux and lactate production in PDC deficiency and, by trans-activating pyruvate dehydrogenase kinase, may further suppress residual PDC activity through phosphorylation of the E1α subunit.

An animal model of PDH deficiency using AAV8-siRNA vector-mediated knockdown of pyruvate dehydrogenase E1α.

We evaluated the feasibility of self-complementary adeno-associated virus (scAAV) vector-mediated knockdown of the pyruvate dehydrogenase complex using small interfering RNAs directed against the E1α subunit gene (PDHA1). AAV serotype 8 was used to stereotaxically deliver scAAV8-si3-PDHA1-Enhanced Green Fluorescent Protein (knockdown) or scAAV8-EGFP (control) vectors into the right striatum and substantia nigra of rats. Rotational asymmetry was employed to quantify abnormal rotation following neurodegeneration in the nigrostriatal system. By 20weeks after surgery, the siRNA-injected rats exhibited higher contralateral rotation during the first 10min following amphetamine administration and lower 90-min total rotations (p≤0.05). Expression of PDC E1α, E1ß and E2 subunits in striatum was decreased (p≤0.05) in the siRNA-injected striatum after 14weeks. By week 25, both PDC activity and expression of E1α were lower (p≤0.05) in siRNA-injected striata compared to controls. E1α expression was associated with PDC activity (R(2)=0.48; p=0.006) and modestly associated with counterclockwise rotation (R(2)=0.51;p=0.07). The use of tyrosine-mutant scAAV8 vectors resulted in ~17-fold increase in transduction efficiency of rat striatal neurons in vivo. We conclude that scAAV8-siRNA vector-mediated knockdown of PDC E1α in brain regions typically affected in humans with PDC deficiency results in a reproducible biochemical and clinical phenotype in rats that may be further enhanced with the use of tyrosine-mutant vectors.

AAV3-mediated transfer and expression of the pyruvate dehydrogenase E1 alpha subunit gene causes metabolic remodeling and apoptosis of human liver cancer cells.

Most cancers rely disproportionately on glycolysis for energy even in the presence of adequate oxygen supply, a condition known as "aerobic glycolysis", or the Warburg effect. Pharmacological reversal of the Warburg effect has been shown to cause selective apoptosis of tumor cells, presumably by stimulating mitochondrial respiratory chain activity and production of reactive oxygen species that, in turn, induce a caspase-mediated series of reactions leading to cell death. We reasoned that a similar effect on tumor cells might result from up-regulation of the E1alpha subunit gene (pda1) of the pyruvate dehydrogenase complex (PDC) that catalyzes the rate-limiting step in aerobic glucose oxidation and thus plays a major role in the control of oxidative phosphorylation. To test this postulate, we employed a self-complementary adeno-associated virus (scAAV)-based delivery and expression system for targeting pda1 to the mitochondria of primary cultures of human hepatoblastoma (HB) and hepatocellular carcinoma (HCC) cells. Serotypes 1-10 scAAV vectors that included enhanced green fluorescent (egfp) reporter gene driven by either cytomegalovirus (CMV) or chicken beta-actin (CBA) promoters were analyzed for transduction ability of HB (Huh-6) and HCC (Huh-7 and HepG2) cell lines and primary cultures of normal human hepatocytes. Serotype 3 scAAV-egfp (scAAV3-egfp) vector was the most efficient and transduced up to 90% of cells. We limited the transgene expression primarily to liver cancer cells by generating scAAV3 vectors that contained the human alpha-fetoprotein promoter (AFP)-driven reporter gene (scAAV3.AFP-egfp) and the potentially therapeutic gene scAAV3.AFP-pda1. Infection of Huh-6 cells by the scAAV3.AFP-pda1 vector increased protein expression of E1alpha, PDC catalytic activity, and late-stage apoptotic cell death. Apoptosis was also associated with increased protein expression of Bcl-X/S, an early marker of apoptosis, and release of cytochrome c into the cytosol of infected HB cells. These data indicate that molecular targeting of mitochondrial oxidative metabolism in liver cancer cells by AAV3-mediated delivery of pda1 holds promise as a novel and effective therapeutic approach for human hepatic tumors.

Human blue-opsin promoter preferentially targets reporter gene expression to rat s-cone photoreceptors.

PURPOSE: To develop a gene therapy system that specifically targets transgene expression to S-cones of the mammalian retina, the authors coupled recombinant AAV-mediated delivery with the use of a human blue-opsin (HB) promoter to drive expression. METHODS: Two regions of the HB promoter sequence, HB569 and HB996, were amplified from human DNA, cloned into an AAV vector cassette upstream of the green fluorescent protein (GFP) gene, and packaged into AAV2 and AAV5 capsids. Eyes of postnatal day (P) 40 to P48 Sprague-Dawley rats were subretinally injected with 2 muL vector. Animals were humanely killed 2 to 3 weeks or 20 months after injection, and the pattern and persistence of GFP expression were analyzed in the treated retinas by immunohistochemistry, Western blotting, and RT-PCR. RESULTS: AAV5.HB.GFP vectors targeted photoreceptor transduction with an efficiency 20-fold higher than analogous serotype 2 vector. Both AAV5.HB.GFP vectors exhibited similar transduction efficiencies with patterns of GFP expression that did not vary depending on the size of the HB promoter used. Transgene expression was exclusively localized to photoreceptors of retinas treated with either vector. Furthermore, GFP expression was observed for at least 20 months. Dual GFP immunostaining with S- or M-opsin antibodies and GFP/PNA labeling revealed that cones coexpressing S-opsin/GFP or M-opsin/GFP constituted 37.5% +/- 8% and 13.5% +/- 3% of the GFP-positive photoreceptors, respectively, whereas rods constituted 49% +/- 5% of the GFP-positive photoreceptors. Because cones constitute approximately 1% of adult rat retinal photoreceptors, it was estimated that the relative transduction efficiency of AAV5.HB.GFP vectors was approximately 100:1 for cones versus rods. CONCLUSIONS: AAV5.HB.GFP vector injected into the subretinal space of Sprague-Dawley rats targeted gene expression to photoreceptor cells with an efficiency approximately 20-fold higher than that for AAV2.HB.GFP. Transgene expression regulated by the human blue cone-promoter persisted at least for 20 months. Cones coexpressing S-opsin and the GFP transgene appeared to prevail, confirming that in addition to having properties of the AAV serotype, the promoter choice is key to fine-tuning transgene delivery and expression in specific retinal cells. The system described here may be effective in a therapeutic setting in which strong S-cone transgene expression is required.

Does recombinant adeno-associated virus-vectored proximal region of mouse rhodopsin promoter support only rod-type specific expression in vivo?

PURPOSE: We have previously found that the -385 to +86 portion of the mouse rod opsin promoter (mOP500) can limit recombinant adeno-associated virus (rAAV)-mediated transgene expression to photoreceptor cells when delivered subretinally. However, the photoreceptor (PR) subtype-specificity of expression remains unclear. Here, we evaluated whether the presence of certain cis-elements in this proximal promoter, such as the rod-specific, neural retina leucine zipper protein (NRL) response element (NRE), can render it a driver of rod-specific expression. METHODS: Subretinal injections of a serotype 5 rAAV vector carrying the green fluorescent protein (GFP) cDNA, driven by mOP500, were administered to male Sprague-Dawley rats at postnatal day (P) 40-48. Two weeks to eight months later, the distribution of GFP-expressing cells in the retina was characterized by GFP-, cone-specific alpha-transducin-immuno-, and peanut agglutinin-lectin histochemistry and by morphological criteria. The same viral suspension was also injected sub-retinally into rhodopsin-knockout rho (-/-) mice either at P18 or P78, and retinas were analyzed by immunohistochemistry and PNA lectin histochemistry two weeks later. RESULTS: GFP reactivity was found exclusively in the outer nuclear layer (ONL) of rat retinas two weeks after treatment, with abundant reporter gene expression observed in both rods and cones. GFP-positive cones, defined by their typical morphology and the co-linearity of PNA-lectin labeling with GFP-immunoreactivity, were found in all regions of the transduced retinas. GFP-positive cones constituted up to 6% of the total GFP-positive photoreceptors. By eight months post-injection, a low level of GFP-reactivity was additionally observed in the inner nuclear layer (INL) and ganglion cell layer. Photoreceptor-specific GFP expression was also seen in the rho (-/-) mice at both ages tested. In pups injected at P18, costaining with PNA-lectin revealed that up to 15% of the GFP-positive photoreceptors were cones. Despite only a single row of photoreceptors remaining in these knockout mice by P90, numerous GFP-positive cones were still present. CONCLUSIONS: Subretinal delivery of rAAV5 harboring a reporter gene driven by mOP500 results in passenger gene expression in both rod and cones, indicating that this promoter is photoreceptor-specific but not rod-specific. The lack of photoreceptor subtype-specificity suggests that although cones do not express the NRL and NR2E3 trans-factors considered necessary for activation of mOP500, other general transcription factors in cones may compensate.