Rajeshwari D. Koilkonda

Gene delivery to mitochondria by targeting modified adenoassociated virus suppresses Leber’s hereditary optic neuropathy in a mouse model

To introduce DNA into mitochondria efficiently, we fused adenoassociated virus capsid VP2 with a mitochondrial targeting sequence to carry the mitochondrial gene encoding the human NADH ubiquinone oxidoreductase subunit 4 (ND4). Expression of WT ND4 in cells with the G11778A mutation in ND4 led to restoration of defective ATP synthesis. Furthermore, with injection into the rodent eye, human ND4 DNA levels in mitochondria reached 80% of its mouse homolog. The construct expressed in most inner retinal neurons, and it also suppressed visual loss and optic atrophy induced by a mutant ND4 homolog. The adenoassociated virus cassette accommodates genes of up to ∼5 kb in length, thus providing a platform for introduction of almost any mitochondrial gene and perhaps even allowing insertion of DNA encompassing large deletions of mtDNA, some associated with aging, into the organelle of adults.

Efficiency and Safety of AAV-Mediated Gene Delivery of the Human ND4 Complex I Subunit in the Mouse Visual System

PURPOSE To evaluate the efficiency and safety of AAV-mediated gene delivery of a normal human ND4 complex I subunit in the mouse visual system. METHODS A nuclear encoded human ND4 subunit fused to the ATPc mitochondrial targeting sequence and FLAG epitope were packaged in AAV2 capsids that were injected into the right eyes of mice. AAV-GFP was injected into the left eyes. One month later, pattern electroretinography (PERG), rate of ATP synthesis, gene expression, and incorporation of the human ND4 subunit into the murine complex I were evaluated. Quantitative analysis of ND4FLAG-injected eyes was assessed compared with green fluorescent protein (GFP)-injected eyes. RESULTS Rates of ATP synthesis and PERG amplitudes were similar in ND4FLAG- and GFP-inoculated eyes. PERG latency was shorter in eyes that received ND4FLAG. Immunoprecipitated murine complex I gave the expected 52-kDa band of processed human ND4FLAG. Confocal microscopy revealed perinuclear expression of FLAG colocalized with mitochondria-specific fluorescent dye. Transmission electron microscopy revealed FLAG immunogold within mitochondria. Compared with Thy1.2-positive retinal ganglion cells (RGCs), quantification was 38% for FLAG-positive RGCs and 65% for GFP-positive RGCs. Thy1.2 positive-RGC counts in AAV-ND4FLAG were similar to counts in control eyes injected with AAV-GFP. CONCLUSIONS Human ND4 was properly processed and imported into the mitochondria of RGCs and axons of mouse optic nerve after intravitreal injection. Although it had approximately two-thirds the efficiency of GFP, the expression of normal human ND4 in murine mitochondria did not induce the loss of RGCs, ATP synthesis, or PERG amplitude, suggesting that allotopic ND4 may be safe for the treatment of patients with Leber hereditary optic neuropathy.

Gene Therapy for Leber Hereditary Optic Neuropathy: Initial Results.

PURPOSE Leber hereditary optic neuropathy (LHON) is a disorder characterized by severe and rapidly progressive visual loss when caused by a mutation in the mitochondrial gene encoding NADH:ubiquinone oxidoreductase subunit 4 (ND4). We have initiated a gene therapy trial to determine the safety and tolerability of escalated doses of an adeno-associated virus vector (AAV) expressing a normal ND4 complementary DNA in patients with a G to A mutation at nucleotide 11778 of the mitochondrial genome. DESIGN In this prospective open-label trial (NCT02161380), the study drug (self-complementary AAV [scAAV]2(Y444,500,730F)-P1ND4v2) was intravitreally injected unilaterally into the eyes of 5 blind participants with G11778A LHON. Four participants with visual loss for more than 12 months were treated. The fifth participant had visual loss for less than 12 months. The first 3 participants were treated at the low dose of vector (5 × 10(9) vg), and the fourth participant was treated at the medium dose (2.46 × 10(10) vg). The fifth participant with visual loss for less than 12 months received the low dose. Treated participants were followed for 90 to 180 days and underwent ocular and systemic safety assessments along with visual structure and function examinations. PARTICIPANTS Five legally blind patients with G11778A LHON. MAIN OUTCOME MEASURES Loss of visual acuity. RESULTS Visual acuity as measured by the Early Treatment Diabetic Retinopathy Study (ETDRS) eye chart remained unchanged from baseline to 3 months in the first 3 participants. For 2 participants with 90-day follow-up, acuity increased from hand movements to 7 letters in 1 and by 15 letters in 1, representing an improvement equivalent to 3 lines. No one lost vision, and no serious adverse events were observed. Minor adverse events included a transient increase of intraocular pressure (IOP), exposure keratitis, subconjunctival hemorrhage, a sore throat, and a transient increase in neutralizing antibodies (NAbs) against AAV2 in 1 participant. All blood samples were negative for vector DNA. CONCLUSIONS No serious safety problems were observed in the first 5 participants enrolled in this phase I trial of virus-based gene transfer in this mitochondrial disorder. Additional study follow-up of these and additional participants planned for the next 4 years is needed to confirm these preliminary observations.

Safety and Effects of the Vector for the Leber Hereditary Optic Neuropathy Gene Therapy Clinical Trial

IMPORTANCE We developed a novel strategy for treatment of Leber hereditary optic neuropathy (LHON) caused by a mutation in the nicotinamide adenine dinucleotide dehydrogenase subunit IV (ND4) mitochondrial gene. OBJECTIVE To demonstrate the safety and effects of the gene therapy vector to be used in a proposed gene therapy clinical trial. DESIGN AND SETTING In a series of laboratory experiments, we modified the mitochondrial ND4 subunit of complex I in the nuclear genetic code for import into mitochondria. The protein was targeted into the organelle by agency of a targeting sequence (allotopic expression). The gene was packaged into adeno-associated viral vectors and then vitreally injected into rodent, nonhuman primate, and ex vivo human eyes that underwent testing for expression and integration by immunohistochemical analysis and blue native polyacrylamide gel electrophoresis. During serial follow-up, the animal eyes underwent fundus photography, optical coherence tomography, and multifocal or pattern electroretinography. We tested for rescue of visual loss in rodent eyes also injected with a mutant G11778A ND4 homologue responsible for most cases of LHON. EXPOSURE Ocular infection with recombinant adeno-associated viral vectors containing a wild-type allotopic human ND4 gene. MAIN OUTCOMES AND MEASURES Expression of human ND4 and rescue of optic neuropathy induced by mutant human ND4. RESULTS We found human ND4 expressed in almost all mouse retinal ganglion cells by 1 week after injection and ND4 integrated into the mouse complex I. In rodent eyes also injected with a mutant allotopic ND4, wild-type allotopic ND4 prevented defective adenosine triphosphate synthesis, suppressed visual loss, reduced apoptosis of retinal ganglion cells, and prevented demise of axons in the optic nerve. Injection of ND4 in the ex vivo human eye resulted in expression in most retinal ganglion cells. Primates undergoing vitreal injection with the ND4 test article and followed up for 3 months had no serious adverse reactions. CONCLUSIONS AND RELEVANCE Expression of our allotopic ND4 vector in the ex vivo human eye, safety of the test article, rescue of the LHON mouse model, and the severe irreversible loss of visual function in LHON support clinical testing with mutated G11778A mitochondrial DNA in our patients.

Leber's Hereditary Optic Neuropathy-Gene Therapy: From Benchtop to Bedside

Lebers hereditary optic neuropathy (LHON) is a maternally transmitted disorder caused by point mutations in mitochondrial DNA (mtDNA). Most cases are due to mutations in genes encoding subunits of the NADH-ubiquinone oxidoreductase that is Complex I of the electron transport chain (ETC). These mutations are located at nucleotide positions 3460, 11778, or 14484 in the mitochondrial genome. The disease is characterized by apoplectic, bilateral, and severe visual loss. While the mutated mtDNA impairs generation of ATP by all mitochondria, there is only a selective loss of retinal ganglion cells and degeneration of optic nerve axons. Thus, blindness is typically permanent. Half of the men and 10% of females who harbor the pathogenic mtDNA mutation actually develop the phenotype. This incomplete penetrance and gender bias is not fully understood. Additional mitochondrial and/or nuclear genetic factors may modulate the phenotypic expression of LHON. In a population-based study, the mtDNA background of haplogroup J was associated with an inverse relationship of low-ATP generation and increased production of reactive oxygen species (ROS). Effective therapy for LHON has been elusive. In this paper, we describe the findings of pertinent published studies and discuss the controversies of potential strategies to ameliorate the disease.

Induction of Rapid and Highly Efficient Expression of the Human ND4 Complex I Subunit in the Mouse Visual System by Self-complementary Adeno-Associated Virus

OBJECTIVE To demonstrate the high efficiency and rapidity of allotopic expression of a normal human ND4 subunit of complex I in the vertebrate retina using a self-complementary adeno-associated virus (scAAV) vector for ocular gene delivery to treat acute visual loss in Leber hereditary optic neuropathy (LHON). METHODS The nuclear-encoded human ND4 subunit fused to the P1 isoform of subunit C of adenosine triphosphate synthase (ATPc) mitochondrial targeting sequence and FLAG epitope was packaged in scAAV2 capsids or single-stranded (ss) AAV2 capsids. These constructs were injected into the vitreous cavities of mice. The contralateral eyes were injected with scAAV-green fluorescent protein (GFP). One week later, pattern electroretinograms and gene expression of the human ND4 subunit and GFP were evaluated. Quantitative analysis of ND4FLAG-injected eyes was assessed relative to Thy1.2-labeled retinal ganglion cells (RGCs). RESULTS Pattern electroretinogram amplitudes remained normal in eyes inoculated with scAAV-ND4FLAG, ssAAV-ND4FLAG, and GFP. Confocal microscopy revealed the typical perinuclear mitochondrial expression of scAAV-ND4FLAG in almost the entire retinal flat mount. In contrast, scAAV-GFP expression was cytoplasmic and nuclear. Relative to Thy1.2-positive RGCs, quantification of scAAV-ND4FLAG-positive RGCs was 91% and that of ssAAV-ND4FLAG-positive RGCs was 51%. CONCLUSION Treatment of acute visual loss due to LHON may be possible with a normal human ND4 subunit gene of complex I, mutated in most cases of LHON, when delivered by an scAAV vector. Clinical Relevance Unlike most retinal degenerations that result in slowly progressive loss of vision over many years, LHON due to mutated mitochondrial DNA results in apoplectic, bilateral severe and usually irreversible visual loss. For rescue of acute visual loss in LHON, a highly efficient and rapid gene expression system is required.

LHON Gene Therapy Vector Prevents Visual Loss and Optic Neuropathy Induced by G11778A Mutant Mitochondrial DNA: Biodistribution and Toxicology Profile

PURPOSE To demonstrate safety and efficacy of allotopic human ND4 for treatment of a Lebers hereditary optic neuropathy (LHON) mouse model harboring the G11778A mitochondrial mutation. METHODS We induced LHON in mice by intravitreal injection of mutant (G11778A) human ND4 DNA, responsible for most cases of LHON, that was directed to mitochondria using an AAV2 vector to which we appended a mitochondrial targeting sequence to the VP2 capsid. We then attempted rescue of visual loss using our test article (ScAAV2-P1ND4v2) containing a synthetic nuclear encoded G11778G ND4 gene that was allotopically expressed. Control mice either were uninjected or received AAV2-GFP or AAV2-mCherry. We performed RT-PCR and confocal microscopy at 2 weeks post injection. Pattern electroretinograms (PERGs), spectral-domain optical coherence tomography (SD-OCT), histology, and transmission electron microscopy (TEM) were performed. For toxicology and biodistribution studies, the test article was administered intravitreally to rats and rhesus macaques at different doses. RESULTS Mutant and wild-type ND4 were efficiently expressed in the mitochondria of retinal ganglion cells (RGCs). Visual function assessed by serial PERGs and retinal structure by serial SD-OCT showed a significant rescue by the test article. Histology and ultrastructural analysis confirmed that loss of RGCs and demise of axons was prevented by ScAAV2-P1ND4v2. Rat and nonhuman primate biodistribution studies showed that vector spread outside the injected eye into spleen and lymph nodes was minimal. Histopathology of tissues and organs including the eyes was comparable to that of uninfected and saline-injected eyes. CONCLUSIONS Allotopically expressed wild-type ND4 prevents the phenotype induced by G11778A mitochondrial DNA with a toxicology profile acceptable for testing in a phase I clinical trial.

Noninvasive Assessments of Optic Nerve Neurodegeneration in Transgenic Mice With Isolated Optic Neuritis

PURPOSE To determine if phosphorylated neurofilament heavy chain (pNF-H) released into the bloodstream and the pattern ERG are noninvasive indicators of neurodegeneration in experimental optic neuritis. METHODS Serum from Myelin oligodendrocyte glycoprotein (MOG)-specific T cell receptor-positive (TCR+) transgenic mice that develop isolated optic neuritis usually without any other characteristic lesions of inflammation or demyelination in the spinal cord and littermates negative for the transgene were assayed for the presence of serum phosphorylated neurofilament H (pNF-H). In vivo measurements of optic nerve and retinal ganglion cell injury were assessed by magnetic resonance imaging (MRI), optical coherence tomography (OCT), and pattern electroretinogram (PERG). Automated two dimensional fluorescence differential in-gel electrophoresis (2D-DIGE) of pooled optic nerve samples, light, and transmission electron micrographs were used to evaluate optic atrophy postmortem. RESULTS We found an almost 3-fold elevation in serum pNF-H levels in MOG+ mice relative to MOG-littermates (P = 0.02). 2D-DIGE revealed a 3-fold reduction in optic nerve neurofilaments. Visual function assessed by the PERG was reduced by one-quarter (P = 0.033) and latencies increased by 38% (P = 0.036). MOG+ mice with the lowest PERG amplitudes had optic nerve atrophy visualized by MRI. Optic nerve diameters were reduced by one-third (P = 0.0001) and axon counts reduced by more than two-thirds. Histopathology of the spinal cords was normal. CONCLUSIONS Elevated serum pNF-H levels and the PERG are useful markers of neurodegeneration of the optic nerve in isolated experimental optic neuritis. Our findings suggest that elevations of this axonal protein in patients with optic neuritis who had a poor visual outcome are likely also due to demise of optic nerve axons.

Consequences of zygote injection and germline transfer of mutant human mitochondrial DNA in mice

Significance Therapies for Leber hereditary optic neuropathy (LHON), in common with all disorders caused by mutated mtDNA, are inadequate, in part because of the absence of suitable animal models. To test a potential therapy, we introduced mutant human NADH ubiquinone oxidoreductase subunit 4 DNA directly into mitochondria of mouse zygotes to generate transgenic LHON mice. This mutation in mice caused the hallmark visual loss and optic neuropathy seen in LHON patients. We reversed the blindness by gene therapy with the wild-type allele. To our knowledge, this is the first description of a mouse model with the same genotype and phenotype as the human counterpart disorder. This innovative technology has implications not only for creating mouse models of mutant mtDNA but also for treating the mitochondrial dysfunction with gene therapy. Considerable evidence supports mutations in mitochondrial genes as the cause of maternally inherited diseases affecting tissues that rely primarily on oxidative energy metabolism, usually the nervous system, the heart, and skeletal muscles. Mitochondrial diseases are diverse, and animal models currently are limited. Here we introduced a mutant human mitochondrial gene responsible for Leber hereditary optic neuropathy (LHON) into the mouse germ line using fluorescence imaging for tissue-specific enrichment in the target retinal ganglion cells. A mitochondria-targeted adeno-associated virus (MTS-AAV) containing the mutant human NADH ubiquinone oxidoreductase subunit 4 (ND4) gene followed by mitochondrial-encoded mCherry was microinjected into zygotes. Female founders with mCherry fluorescence on ophthalmoscopy were backcrossed with normal males for eight generations. Mutant human ND4 DNA was 20% of mouse ND4 and did not integrate into the host genome. Translated human ND4 protein assembled into host respiratory complexes, decreasing respiratory chain function and increasing oxidative stress. Swelling of the optic nerve head was followed by progressive demise of ganglion cells and their axons, the hallmarks of human LHON. Early visual loss that began at 3 mo and progressed to blindness 8 mo after birth was reversed by intraocular injection of MTS-AAV expressing wild-type human ND4. The technology of introducing human mitochondrial genes into the mouse germ line has never been described, to our knowledge, and has implications not only for creating animal models recapitulating the counterpart human disorder but more importantly for reversing the adverse effects of the mutant gene using gene therapy to deliver the wild-type allele.

Complex I Subunit Gene Therapy With NDUFA6 Ameliorates Neurodegeneration in EAE

PURPOSE To address the permanent disability induced by mitochondrial dysfunction in experimental autoimmune encephalomyelitis (EAE). METHODS Mice sensitized for EAE were rescued by intravitreal injection of adeno-associated viral vector serotype 2 with the complex I subunit gene scAAV-NDUFA6Flag. Controls were injected with a mitochondrially targeted red fluorescent protein (scAAV-COX8-cherry). Another group received scAAV-COX8-cherry, but was not sensitized for EAE. Serial pattern electroretinograms (PERGs) and optical coherent tomography (OCT) evaluated visual function and structure of the retina at 1, 3, and 6 months post injection (MPI). Treated mice were killed 6 MPI for histopathology. Immunodetection of cleaved caspase 3 gauged apoptosis. Complex I activity was assessed spectrophotometrically. Expression of NDUFA6Flag in the retina and optic nerve were evaluated between 1 week to 1 month post injection by RT-PCR, immunofluorescence and immunoblotting. RESULTS Reverse transcription-PCR and immunoblotting confirmed NDUFA6Flag overexpression with immunoprecipitation and blue native PAGE showing integration into murine complex I. Overexpression of NDUFA6Flag in the visual system of EAE mice rescued retinal complex I activity completely, axonal loss by 73%, and retinal ganglion cell (RGC) loss by 88%, RGC apoptosis by 66%, and restored the 33% loss of complex I activity in EAE to normal levels; thereby, preventing loss of vision indicated by the 43% reduction in the PERG amplitudes of EAE mice. CONCLUSIONS NDUFA6 gene therapy provided long-term suppression of neurodegeneration in the EAE animal model suggesting that it may also ameliorate the mitochondrial dysfunction associated with permanent disability in optic neuritis and MS patients.