Conserved as well as divergent regulatory elements account for expression of the human and rodent phenylalanine hydroxylase genes

Low-Dose Gene Therapy for Murine PKU Using Episomal Naked DNA Vectors Expressing PAH from Its Endogenous Liver Promoter

Limited duration of transgene expression, insertional mutagenesis, and size limitations for transgene cassettes pose challenges and risk factors for many gene therapy vectors. Here, we report on physiological expression of liver phenylalanine hydroxylase (PAH) by delivery of naked DNA/minicircle (MC)-based vectors for correction of homozygous enu2 mice, a model of human phenylketonuria (PKU). Because MC vectors lack a defined size limit, we constructed a MC vector expressing a codon-optimized murine Pah cDNA that includes a truncated intron and is under the transcriptional control of a 3.6-kb native Pah promoter/enhancer sequence. This vector, delivered via hydrodynamic injection, yielded therapeutic liver PAH activity and sustained correction of blood phenylalanine comparable to viral or synthetic liver promoters. Therapeutic efficacy was seen with vector copy numbers of <1 vector genome per diploid hepatocyte genome and was achieved at a vector dose that was significantly lowered. Partial hepatectomy and subsequent liver regeneration was associated with >95% loss of vector genomes and PAH activity in liver, demonstrating that MC vectors had not integrated into the liver genome. In conclusion, MC vectors, which do not have a defined size-limitation, offer a favorable safety profile for hepatic gene therapy due to their non-integration in combination with native promoters.

Serum amino acids in patients with mutations in the hepatocyte nuclear factor-1 alpha gene

AIMS

Knockout mice lacking both copies of the hepatocyte nuclear factor 1 (HNF1) gene have altered serum levels of amino acids and generalized aminoaciduria. The aim of our study was to test whether alterations in serum amino acid levels were found in patients with mutations in the hepatocyte nuclear factor-1 alpha (HNF-1alpha) gene compared with controls.

METHODS

Fasting serum from 20 patients with HNF-1alpha mutations and 20 age, sex and body mass index-matched controls was analysed for 16 amino acids. Means were compared between the two groups and Z scores calculated.

RESULTS

There was no significant difference between patients with HNF-1alpha mutations and controls in serum levels of phenylalanine, arginine, citrulline or lysine as suggested by knockout mice models. Although serum levels of eight amino acids were different in the two groups, these were not significant after Bonferroni correction.

CONCLUSIONS

The alterations in serum amino acid levels seen in mice models are not seen in patients with mutations in the HNF-1alpha gene. This suggests differences in mouse and man in the regulation of amino acid transport and has not provided us with a phenotypic marker to use before confirmatory genetic testing.

In silico searching of human and mouse genome data identifies known and unknown HNF1 binding sites upstream of beta-cell genes

HNF1-alpha is a transcription factor present in beta-cells. Mutations in the HNF1-alpha gene cause maturity-onset diabetes of the young (MODY), but the exact mechanism is not known. Several studies have highlighted genes down-regulated in beta-cells lacking this gene, but it is not clear if these are directly regulated by HNF1-alpha. To better understand this, we used human and mouse genome data to examine 29 genes expressed in the beta-cell. Using an in silico approach (with software available at www.BindGene.org) we examined 2kb upstream of each gene for possible HNF1 binding sequences. In five genes we also examined 100kb upstream of each gene, but only the portions strongly conserved between humans and mice. We identified nine putative HNF1 binding sites upstream of seven genes (p<0.1 and good alignment between species or p<0.05). Six of these nine sites had some experimental corroboratory evidence and included the recently identified sites 6 and 45kb upstream of HNF4-alpha. Three novel sites were identified. These were 92bp upstream of SLC3A1, 52bp upstream of PCBD (DCOH), and 42202bp upstream of TCF2(HNF1-beta). In conclusion, our computer search identified some known HNF1 sites, and suggested three novel sites indicating these genes are very likely to be directly activated by HNF1. This should help in designing experiments to discover the mechanisms of beta-cell dysfunction due to HNF1 disruption.