The ability of the gut hormone ghrelin to promote positive energy balance is mediated by the growth hormone secretagogue receptor (GHSR). GHSR is a G protein-coupled receptor (GPCR) that is found centrally and peripherally and that can signal in a ligand-independent manner basally or when heterodimerized with other GPCRs. However, current Ghsr knockout models cannot dissect ghrelindependent and -independent signaling, precluding assessment of the physiological importance of these signaling pathways. An animal model carrying a Ghsr mutation that preserves GHSR cell surface abundance, but selectively alters GHSR signaling, would be a useful tool to decipher GHSR signaling in vivo. We used rats with the Ghsr Q343X mutation (Ghsr M/M ), which is predicted to delete the distal part of the GHSR C-terminus tail, a domain critical for the signal termination processes of receptor internalization and -arrestin recruitment. In cells, the Q343X GHSR mutant showed enhanced ligandinduced G protein-dependent signaling and blunted activity of processes involved in GPCR signal termination. Ghsr M/M rats displayed enhanced responses to submaximal doses of ghrelin or GHSR agonist. Moreover, Ghsr M/M rats had a more stable body weight under caloric restriction, a condition that increases endogenous ghrelin tone, whereas under standard housing conditions, Ghsr M/M rats showed increased body weight, adiposity and reduced glucose tolerance. Overall, our data stresses the physiological role of the distal domain of GHSR C-terminus as a suppressor of ghrelin sensitivity and we propose using the Ghsr M/M rat as a physiological model of gain-of-function in Ghsr to identify treatments for obesity-related conditions.3

Neovascular age-related macular degeneration (nvAMD) is characterized by choroidal blood vessels growing into the subretinal space, leading to retinal pigment epithelial (RPE) cell degeneration and vision loss. Vessel growth results from an imbalance of pro-angiogenic (e.g., vascular endothelial growth factor [VEGF]) and anti-angiogenic factors (e.g., pigment epithelium-derived factor [PEDF]). Current treatment using intravitreal injections of anti-VEGF antibodies improves vision in about 30% of patients but may be accompanied by side effects and non-compliance. To avoid the difficulties posed by frequent intravitreal injections, we have proposed the transplantation of pigment epithelial cells modified to overexpress human PEDF. Stable transgene integration and expression is ensured by the hyperactive Sleeping Beauty transposon system delivered by pFAR4 miniplasmids, which have a backbone free of antibiotic resistance markers. We demonstrated efficient expression of the PEDF gene and an optimized PEDF cDNA sequence in as few as 5 × 103 primary cells. At 3 weeks post-transfection, PEDF secretion was significantly elevated and long-term follow-up indicated a more stable secretion by cells transfected with the optimized PEDF transgene. Analysis of transgene insertion sites in human RPE cells showed an almost random genomic distribution. The results represent an important contribution toward a clinical trial aiming at a non-viral gene therapy of nvAMD.

Mucopolysaccharidosis type IIIA (MPS-IIIA) or Sanfilippo A syndrome is a lysosomal storage genetic disease that results from the deficiency of the N-sulfoglucosamine sulfohydrolase (SGSH) protein, a sulfamidase required for the degradation of heparan sulfate glycosaminoglycans (GAGs). The accumulation of these macromolecules leads to somatic organ pathologies, severe neurodegeneration and death. To assess a novel gene therapy approach based on prolonged secretion of the missing enzyme by the liver, mediated by hydrodynamic gene delivery, we first compared a kanamycin and an antibiotic-free expression plasmid vector, called pFAR4. Thanks to the reduced vector size, pFAR4 derivatives containing either a ubiquitous or a liver-specific promoter mediated a higher reporter gene expression level than the control plasmid. Hydrodynamic delivery of SGSH-encoding pFAR4 into MPS-IIIA diseased mice led to high serum levels of sulfamidase protein that was efficiently taken up by neighboring organs, as shown by the correction of GAG accumulation. A similar reduction in GAG content was also observed in the brain, at early stages of the disease. Thus, this study contributes to the effort towards the development of novel biosafe non-viral gene vectors for therapeutic protein expression in the liver, and represents a first step towards an alternative gene therapy approach for the MPS-IIIA disease.

The anti-angiogenic and neurogenic pigment epithelium-derived factor (PEDF) demonstrated a potency to control choroidal neovascularization in age-related macular degeneration (AMD) patients. The goal of the present study was the development of an efficient and safe technique to integrate, ex vivo, the PEDF gene into retinal pigment epithelial (RPE) cells for later transplantation to the subretinal space of AMD patients to allow continuous PEDF secretion in the vicinity of the affected macula. Because successful gene therapy approaches require efficient gene delivery and stable gene expression, we used the antibiotic-free pFAR4 mini-plasmid vector to deliver the hyperactive Sleeping Beauty transposon system, which mediates transgene integration into the genome of host cells. In an initial study, lipofection-mediated co-transfection of HeLa cells with the SB100X transposase gene and a reporter marker delivered by pFAR4 showed a 2-fold higher level of genetically modified cells than when using the pT2 vectors. Similarly, with the pFAR4 constructs, electroporation-mediated transfection of primary human RPE cells led to 2.4-fold higher secretion of recombinant PEDF protein, which was still maintained 8 months after transfection. Thus, our results show that the pFAR4 plasmid is a superior vector for the delivery and integration of transgenes into eukaryotic cells.

Non-viral gene delivery into the liver generally mediates a transient transgene expression. A comparative analysis was performed using two gene vectors, pFAR4 and pKAR4, which differ by the absence or presence of an antibiotic resistance marker, respectively. Both plasmids carried the same eukaryotic expression cassette composed of a sulfamidase (Sgsh) cDNA expressed from the human alpha antitrypsin liver-specific promoter. Hydrodynamic injection of the pFAR4 construct resulted in prolonged sulfamidase secretion from the liver, whereas delivery of the pKAR4 construct led to a sharp decrease in circulating enzyme. After induction of hepatocyte division, a rapid decline of sulfamidase expression occurred, indicating that the pFAR4 derivative was mostly episomal. Quantification analyses revealed that both plasmids were present at similar copy numbers, whereas Sgsh transcript levels remained high only in mice infused with the pFAR4 construct. Using a chromatin immunoprecipitation assay, it was established that the 5 0 end of the expression cassette carried by pKAR4 exhibited a 7.9-fold higher heterochromatin-toeuchromatin ratio than the pFAR4 construct, whereas a bisulfite treatment did not highlight any obvious differences in the methylation status of the two plasmids. Thus, by preventing transgene expression silencing, the pFAR4 gene vector allows a sustained transgene product secretion from the liver.

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