p75 reduces beta-amyloid-induced sympathetic innervation deficits in an Alzheimer's disease mouse model.

Beta-amyloid (Abeta) has adverse effects on brain cells, but little is known about its effects on the peripheral nervous system in Alzheimer's disease (AD). Several lines of in vitro evidence suggest that the neurotrophin receptor p75 mediates or exacerbates Abeta-induced neurotoxicity. Here, we show that p75-deficient sympathetic neurons are more sensitive to Abeta-induced neurite growth inhibition. To investigate the role of p75 in the sympathetic nervous system of AD, p75 mutant mice were crossed with a mouse line of AD model. The majority of p75-deficient AD mice died by 3 weeks of age. The lethality is associated with severe defects in sympathetic innervation to multiple organs. When 1 copy of the BACE1 gene encoding a protein essential in Abeta production was deleted in p75-deficient AD mice, sympathetic innervation was significantly restored. These results suggest that p75 is neuroprotective for the sympathetic nervous system in a mouse model of AD.

Targeting of the ETS factor GABPalpha disrupts neuromuscular junction synaptic function.

The GA-binding protein (GABP) transcription factor has been shown in vitro to regulate the expression of the neuromuscular proteins utrophin, acetylcholine esterase, and acetylcholine receptor subunits delta and epsilon through the N-box promoter motif (5'-CCGGAA-3'), but its in vivo function remains unknown. A single point mutation within the N-box of the gene encoding the acetylcholine receptor epsilon subunit has been identified in several patients suffering from postsynaptic congenital myasthenic syndrome, implicating the GA-binding protein in neuromuscular function and disease. Since conventional gene targeting results in an embryonic-lethal phenotype, we used conditional targeting to investigate the role of GABPalpha in neuromuscular junction and skeletal muscle development. The diaphragm and soleus muscles from mutant mice display alterations in morphology and distribution of acetylcholine receptor clusters at the neuromuscular junction and neurotransmission properties consistent with reduced receptor function. Furthermore, we confirmed decreased expression of the acetylcholine receptor epsilon subunit and increased expression of the gamma subunit in skeletal muscle tissues. Therefore, the GABP transcription factor aids in the structural formation and function of neuromuscular junctions by regulating the expression of postsynaptic genes.

"B in IT" - a community-based model for the management of hepatitis B patients in primary care clinics using a novel web-based clinical tool.

BACKGROUND: The current model of care for the treatment of chronic hepatitis B (CHB) in Australia is through specialist Hepatology or Infectious Diseases clinics, and limited accredited primary care practices. Capacity is limited, and less than 5% of Australians living with CHB currently access therapy. Increasing treatment uptake is an urgent area of clinical need. Nucleos(t)ide analogue therapy is safe and effective treatment for CHB that is suitable for community prescribing. We have evaluated the success of a community-based model for the management of CHB in primary care clinics using a novel web-based clinical tool. METHODS: Using guidelines set out by the Gastroenterological Society of Australia, we developed an interactive online clinical management tool for the shared care of patients with CHB in primary care clinics, with remote oversight from tertiary hospital-based hepatologists and a project officer. We call this model of care the "B in IT" program. Suitable patients were referred from the specialist liver clinic back to primary care for ongoing management. Compliance with recommended appointments, pathology tests and ultrasounds of patients enrolled in "B in IT" was assessed and compared to that of the same patients prior to community discharge, as well as a matched control group of CHB outpatients continuing to attend a specialist clinic. RESULTS: Thirty patients with CHB were enrolled in the "B in IT" program. Compliance with attending scheduled appointments within 1 month of the suggested date was 87% across all 115 visits scheduled. Compliance with completing recommended pathology within 1 month of the suggested date was 94% and compliance with completing recommended liver ultrasounds for cancer screening within 1 month of the suggested date was 89%. The compliance rates for visit attendance and ultrasound completion were significantly higher than the control patient group (p < 0.0001) and the "B in IT" patients prior to community discharge (p = 0.002 and p = 0.039, respectively). CONCLUSIONS: The "B in IT" program's novel web-based clinical tool supports primary care physicians to treat and monitor patients with CHB. This program promotes community-based care and increases system capacity for the clinical care of people living with CHB.

The ETS transcription factor GABPalpha is essential for early embryogenesis.

The ETS transcription factor complex GABP consists of the GABPalpha protein, containing an ETS DNA binding domain, and an unrelated GABPbeta protein, containing a transactivation domain and nuclear localization signal. GABP has been shown in vitro to regulate the expression of nuclear genes involved in mitochondrial respiration and neuromuscular signaling. We investigated the in vivo function of GABP by generating a null mutation in the murine Gabpalpha gene. Embryos homozygous for the null Gabpalpha allele die prior to implantation, consistent with the broad expression of Gabpalpha throughout embryogenesis and in embryonic stem cells. Gabpalpha(+/-) mice demonstrated no detectable phenotype and unaltered protein levels in the panel of tissues examined. This indicates that Gabpalpha protein levels are tightly regulated to protect cells from the effects of loss of Gabp complex function. These results show that Gabpalpha function is essential and is not compensated for by other ETS transcription factors in the mouse, and they are consistent with a specific requirement for Gabp expression for the maintenance of target genes involved in essential mitochondrial cellular functions during early cleavage events of the embryo.

Tissue-specific overexpression of the HSA21 gene GABPalpha: implications for DS.

The ETS transcription factor GABPalpha is encoded by a gene on HSA21 and interacts with an ankyrin repeat-containing beta subunit to form the GABP complex. GABP regulates expression of genes involved in mitochondrial respiration and neuromuscular signalling. When GABPalpha mRNA is overexpressed in human DS fibroblast cell lines, or by tranfection in NIH3T3 cells, no increase in protein level is detected. However, increased Gabpalpha gene dosage in the Ts65Dn segmental trisomy mouse model of DS (DS) results in elevated Gabpalpha protein levels in brain and skeletal muscle only. These findings suggest that GABPalpha protein levels are tightly regulated in a tissue-specific manner, and consequently GABP may play a role in DS pathologies in tissues where GABPalpha protein levels are elevated.

Identification and expression analysis of alternative transcripts of the mouse GA-binding protein (Gabp) subunits alpha and beta1.

The erythroblast transformation specific (ETS) transcription factor GA-binding protein (Gabp) is widely expressed and acts on a diverse range of target genes, including nuclear-encoded mitochondrial proteins and neuromuscular-specific genes. The GABPalpha subunit contains an ETS DNA binding domain and the beta subunit contains a nuclear localization signal (NLS) and transactivation domain. Here, we show coincident expression of Gabpalpha and beta1 throughout mouse embryogenesis, consistent with the gene products functioning in a complex. We have also identified 2 alternatively spliced, tissue-specific exons 1 (5' untranslated regions) of mouse Gabpalpha and 4 alternative 3' polyadenylation signals that, in combination, result in 12 transcripts for Gabpalpha. These alternative transcripts are suggested to have altered stability, subcellular localization and/or translation efficiency. Further, we identified nine differentially expressed splice variants of mouse Gabpbeta1 that encode beta protein forms lacking functional domains, suggesting a dominant negative function. Together, alternative transcripts of Gabpalpha and beta1 provide a mechanism for tissue-specific regulation of Gabp activity.

HTS-Compatible Patient-Derived Cell-Based Assay to Identify Small Molecule Modulators of Aberrant Splicing in Myotonic Dystrophy Type 1.

Myotonic dystrophy type 1 (DM1) is a genetic disorder characterized by muscle wasting, myotonia, cataracts, cardiac arrhythmia, hyperinsulinism and intellectual deficits, and is caused by expansion of a CTG repeat in the 3'UTR of the Dystrophia Myotonica-Protein Kinase (DMPK) gene. The DMPK transcripts containing expanded CUG repeats accumulate in nuclear foci and ultimately cause mis-splicing of secondary genes through the dysregulation of RNA-binding proteins including Muscleblind 1 (MBNL1) and CUG binding protein 1 (CUGBP1). Correction of mis-splicing of genes such as the Skeletal muscle-specific chloride channel 1 (CLCN1), Cardiac troponin T (TNNT2), Insulin receptor (INSR) and Sarcoplasmic/endoplasmic reticulum Ca(2+)ATPase 1 (SERCA1) may alleviate some of the symptoms of DM1; hence identification of small molecule modulators is an important step towards a therapy for DM1 patients. Here we describe the generation of immortalized myoblast cell lines derived from healthy (DMPK CTG(5)) and DM1 patient (DMPK CTG(1000)) fibroblasts by constitutive overexpression of human telomerase reverse transcriptase (hTERT) and inducible overexpression of the Myoblast determination factor (MYOD). MBNL1-containing nuclear foci, mis-splicing events and defective myotube differentiation defects characteristic of DM1 were observed in these cells. A CLCN1 luciferase minigene construct (CLCN1-luc) was stably introduced to monitor intron 2 retention in the DM1 cellular context (a reported splicing defect in DM1). The assay was validated by performing a high-throughput screen (HTS) of ~13,000 low molecular weight compounds against the CLCN1-luc DM1 myoblast cell line, providing an ideal system for conducting HTS to better understand and treat DM1.

Identification of small molecule and genetic modulators of AON-induced dystrophin exon skipping by high-throughput screening.

One therapeutic approach to Duchenne Muscular Dystrophy (DMD) recently entering clinical trials aims to convert DMD phenotypes to that of a milder disease variant, Becker Muscular Dystrophy (BMD), by employing antisense oligonucleotides (AONs) targeting splice sites, to induce exon skipping and restore partial dystrophin function. In order to search for small molecule and genetic modulators of AON-dependent and independent exon skipping, we screened approximately 10,000 known small molecule drugs, >17,000 cDNA clones, and >2,000 kinase- targeted siRNAs against a 5.6 kb luciferase minigene construct, encompassing exon 71 to exon 73 of human dystrophin. As a result, we identified several enhancers of exon skipping, acting on both the reporter construct as well as endogenous dystrophin in mdx cells. Multiple mechanisms of action were identified, including histone deacetylase inhibition, tubulin modulation and pre-mRNA processing. Among others, the nucleolar protein NOL8 and staufen RNA binding protein homolog 2 (Stau2) were found to induce endogenous exon skipping in mdx cells in an AON-dependent fashion. An unexpected but recurrent theme observed in our screening efforts was the apparent link between the inhibition of cell cycle progression and the induction of exon skipping.