Treatment of metabolic disorders using genomic technologies: Lessons from methylmalonic acidemia

Hereditary methylmalonic acidemia (MMA) caused by deficiency of the enzyme methylmalonyl-CoA mutase (MMUT) is a relatively common and severe organic acidemia. The recalcitrant nature of the condition to conventional dietary and medical management has led to the use of elective liver and combined liver-kidney transplantation in some patients. However, liver transplantation is intrinsically limited by organ availability, the risks of surgery, procedural and life-long management costs, transplant comorbidities, and a remaining underlying risk of complications related to MMA despite transplantation. Here, we review pre-clinical studies that present alternative approaches to solid organ transplantation as a treatment for MMUT MMA, including adeno-associated viral gene addition therapy, mRNA therapy, and genome editing, with and without nuclease enhancement.

14-kDa phosphohistidine phosphatase is a potential therapeutic target for liver fibrosis

Liver fibrosis, a major cause of morbidity and mortality worldwide, leads to liver damage, seriously threatening human health. In our previous study, we demonstrated that 14 kDa phosphohistidine phosphatase (PHP14) was upregulated in fibrotic liver tissue and involved in the migration and lamellipodia formation of hepatic stellate cells (HSCs). In this study, we evaluated PHP14 as a therapeutic target for liver fibrosis and investigated the mechanism by which it mediates liver fibrosis. AAV-shPhpt1 administration significantly attenuates CCl₄-induced liver fibrosis in mice. In particular, fibrosis-associated inflammatory infiltration was significantly suppressed after PHP14 knockdown. Mechanistically, PHP14 regulated macrophage recruitment, infiltration, and migration by affecting podosome formation of macrophages. Inhibition of PHP14 decreased the expression of the fibrogenic signature at the early stage of liver fibrogenesis and the activation of HSCs in vivo. Thus, PHP14 can be considered a potential therapeutic target for liver fibrosis.NEW & NOTEWORTHY PHP14 inhibition via adeno-associated virus (AAV)-mediated gene silencing could potently attenuate carbon tetrachloride (CCl₄)-induced liver fibrosis. PHP14 could regulate the migration of macrophages to the site of injury in vivo. PHP14 knockdown in vivo influenced the environment of fibrogenesis and relevant signaling pathways, subsequently affecting myofibroblast activation.

Gene Therapy for Hemophilia A: Where We Stand

Hemophilia A (HA) is a hereditary hemorrhagic disease caused by a deficiency of coagulation factor VIII (FVIII) in blood plasma. Patients with HA usually suffer from spontaneous and recurrent bleeding in joints and muscles, or even intracerebral hemorrhage, which might lead to disability or death. Although the disease is currently manageable via delivery of plasma-derived or recombinant FVIII, this approach is costly, and neutralizing antibodies may be generated in a large portion of patients, which render the regimens ineffective and inaccessible. Given the monogenic nature of HA and that a slight increase in FVIII can remarkably alleviate the phenotypes, HA has been considered to be a suitable target disease for gene therapy. Consequently, the introduction of a functional F8 gene copy into the appropriate target cells via viral or nonviral delivery vectors, including gene correction through genome editing approaches, could ultimately provide an effective therapeutic method for HA patients. In this review, we discuss the recent progress of gene therapy for HA with viral and nonviral delivery vectors, including piggyBac, lentiviral and adeno-associated viral vectors, as well as new raising issues involving liver toxicity, pre-existing neutralizing antibodies of viral approach, and the selection of the target cell type for nonviral delivery.

Molecular Strategies for RPGR Gene Therapy

Mutations affecting the Retinitis Pigmentosa GTPase Regulator (RPGR) gene are the commonest cause of X-linked and recessive retinitis pigmentosa (RP), accounting for 10%-20% of all cases of RP. The phenotype is one of the most severe amongst all causes of RP, characteristic for its early onset and rapid progression to blindness in young people. At present there is no cure for RPGR-related retinal disease. Recently, however, there have been important advances in RPGR research from bench to bedside that increased our understanding of RPGR function and led to the development of potential therapies, including the progress of adeno-associated viral (AAV)-mediated gene replacement therapy into clinical trials. This manuscript discusses the advances in molecular research, which have connected the RPGR protein with an important post-translational modification, known as glutamylation, that is essential for its optimal function as a key regulator of photoreceptor ciliary transport. In addition, we review key pre-clinical research that addressed challenges encountered during development of therapeutic vectors caused by high infidelity of the RPGR genomic sequence. Finally, we discuss the structure of three current phase I/II clinical trials based on three AAV vectors and RPGR sequences and link the rationale behind the use of the different vectors back to the bench research that led to their development.

Pre-existing interleukin 10 in cerebral arteries attenuates subsequent brain injury caused by ischemia/reperfusion

Recurrent stroke is difficult to treat and life threatening. Transfer of anti-inflammatory gene is a potential gene therapy strategy for ischemic stroke. Using recombinant adeno-associated viral vector 1 (rAAV1)-mediated interleukin 10 (IL-10), we investigated whether transfer of beneficial gene into the rat cerebral vessels during interventional treatment for initial stroke could attenuate brain injury caused by recurrent stroke. Male Wistar rats were administered rAAV1-IL-10, rAAV1-YFP, or saline into the left cerebral artery. Three weeks after gene transfer, rats were subjected to occlusion of the left middle cerebral artery (MCAO) for 45 min followed by reperfusion for 24 h. IL-10 levels in serum were significantly elevated 3 weeks after rAAV1-IL-10 injection, and virus in the cerebral vessels was confirmed by in situ hybridization. Pre-existing IL-10 but not YFP decreased the neurological dysfunction scores, brain infarction volume, and the number of injured neuronal cells. AAV1-IL-10 transduction increased heme oxygenase (HO-1) mRNA and protein levels in the infarct boundary zone of the brain. Thus, transduction of the IL-10 gene in the cerebral artery prior to ischemia attenuates brain injury caused by ischemia/reperfusion in rats. This preventive approach for recurrent stroke can be achieved during interventional treatment for initial stroke.

Obstacles and future of gene therapy for hemophilia

INTRODUCTION

The recent success of early-phase clinical trials for adeno-associated viral (AAV) liver-directed gene therapy for hemophilia B (HB) demonstrates the potential for gene therapy, in the future, to succeed protein-based prophylaxis therapy for HB. Significant obstacles, however, need to be overcome prior to widespread adoption. The largest obstacles include immune responses to the AAV capsid including preexisting neutralizing antibodies (NAbs) and a delayed cellular immune response. Emerging evidence suggests that the latter is vector-dose dependent. Furthermore, the development and eradication of inhibitors remains a significant safety concern. Similarly, biological differences between Factor VIII and Factor IX (FIX) impose challenges to direct adoption of the successes for HB to hemophilia A (HA).

AREAS COVERED

The advantages and limitations of the current strategies addressing these obstacles for gene therapy for HB and HA are discussed, as well as vector manufacturing issues relevant to widespread adoption. Alternative strategies including both ex-vivo and in-vivo lentiviral-based methods are discussed, though we focus on AAV-based approaches because of their recent clinical success and potential.

EXPERT OPINION

Our opinion is that these obstacles can be overcome with current approaches, and AAV-based gene therapy for HB will likely translate into future clinical care. Innovative approaches are, however, likely needed to solve the current problems obstructing HA gene therapy.

Redirection of doublecortin-positive cell migration by over-expression of the chemokines MCP-1, MIP-1α and GRO-α in the adult rat brain

Inflammation-induced chemoattraction plays a major role in adult subventricular zone (SVZ)-derived precursor cell migration following neural cell loss, in particular through the release of chemokines by activated microglia and macrophages. We previously demonstrated that monocyte chemotactic protein-1 (MCP-1) (chemokine (c-c motif) ligand (CCL)2), macrophage inflammatory protein-1α (MIP-1α) (CCL3) and growth regulatory protein-α (GRO-α) (chemokine (c-x-c motif) ligand (CXCL)1) are up-regulated following neural cell loss in the adult striatum and act as potent chemoattractants for SVZ-derived precursor cells in vitro. Based on these observations, the current study aimed to examine the individual effect of MCP-1, MIP-1α and GRO-α on the migration of adult SVZ-derived neural precursor cells in vivo. To address this without the confounding effects of injury-induced chemotactic cues, adeno-associated viral (AAV)2-mediated in vivo gene transfer was used to ectopically express either MCP-1, MIP-1α or GRO-α, or the control red fluorescent protein (RFP) in the normal adult rat striatum. The extent of doublecortin (Dcx)-positive cell recruitment from the SVZ into the striatal parenchyma was then determined at 4 and 8weeks following AAV2 injection. Ectopic expression either of MCP-1 or MIP-1α in the normal adult rat brain significantly increased the number of Dcx-positive cells and the extent of their migration into the striatum at both 4 and 8weeks after vector injection but did not promote either precursor cell proliferation or neural differentiation. In contrast, while over-expression of GRO-α 4weeks after vector injection induced a significant increase in Dcx-positive cell migration compared to control, this effect was reduced to control levels by 8weeks post injection. Further, direct comparison between MCP-1, MIP-1α and GRO-α at both 4 and 8weeks post vector injection indicated that GRO-α may have a reduced effect in inducing Dcx-positive cell migration when compared to MCP-1. Combined, these results confirm that over-expression of the chemokines MCP-1, MIP-1α and GRO-α can override cues directing precursor cell migration along the rostral migratory stream (RMS) and provides a mechanism by which neural precursor cell migration can be redirected into a non-neurogenic region. Differences in the migratory effect observed between individual chemokine may be due to ligand-binding affinity and/or receptor expression on SVZ-derived precursor cells.

Ursolic acid improves domoic acid-induced cognitive deficits in mice

Our previous findings suggest that mitochondrial dysfunction is the mechanism underlying cognitive deficits induced by domoic acid (DA). Ursolic acid (UA), a natural triterpenoid compound, possesses many important biological functions. Evidence shows that UA can activate PI3K/Akt signaling and suppress Forkhead box protein O1 (FoxO1) activity. FoxO1 is an important regulator of mitochondrial function. Here we investigate whether FoxO1 is involved in the oxidative stress-induced mitochondrial dysfunction in DA-treated mice and whether UA inhibits DA-induced mitochondrial dysfunction and cognitive deficits through regulating the PI3K/Akt and FoxO1 signaling pathways. Our results showed that FoxO1 knockdown reversed the mitochondrial abnormalities and cognitive deficits induced by DA in mice through decreasing HO-1 expression. Mechanistically, FoxO1 activation was associated with oxidative stress-induced JNK activation and decrease of Akt phosphorylation. Moreover, UA attenuated the mitochondrial dysfunction and cognitive deficits through promoting Akt phosphorylation and FoxO1 nuclear exclusion in the hippocampus of DA-treated mice. LY294002, an inhibitor of PI3K/Akt signaling, significantly decreased Akt phosphorylation in the hippocampus of DA/UA mice, which weakened UA actions. These results suggest that UA could be recommended as a possible candidate for the prevention and therapy of cognitive deficits in excitotoxic brain disorders.