Handling of human short-chain acyl-CoA dehydrogenase (SCAD) variant proteins in transgenic mice

Adeno-associated virus-delivered polycistronic microRNA-clusters for knockdown of vascular endothelial growth factor in vivo

BACKGROUND

Vascular endothelial growth factor (VEGF) is an angiogenic growth factor that plays a critical role in several diseases, including cancer, rheumatoid arthritis and diseases of the eye. Persistent regulation of VEGF by expression of small interfering RNAs targeting VEGF represents a potential future strategy for treatment of such diseases. As a step toward this goal, the present study combines the potency of VEGF-targeted miRNA mimics, produced from a miRNA cluster, with delivery by adeno-associated virus (AAV)-based vectors.

METHODS

Nine different engineered tri-cistronic miRNA clusters encoding anti-VEGF effectors were generated and tested in adult human retinal pigment epithelial (ARPE-19) cells using Renilla luciferase screening, quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), western blotting and immunostaining analysis. In vivo efficacy was tested by the injection of scAAV2/8 vectors expressing the most effective miRNA cluster into murine hindlimb muscles, followed by quantitative RT-PCR.

RESULTS

Plasmids containing anti-VEGF miRNA clusters showed efficient silencing of VEGF and demonstrated a combined gene silencing effect for miRNA clusters composed of multiple miRNA-mimicked RNA interference effectors. The most potent molecule, miR-5,10,7, resulted in a knockdown of VEGF by approximately 75%. Injection of scAAV2/8 vectors expressing miR-5,10,7 into murine hindlimb muscles, resulted in a 44% reduction of endogenous VEGF.

CONCLUSIONS

We have developed miRNA clusters encoding anti-VEGF effectors and shown, in a mouse model, that VEGF is efficiently down-regulated by scAAV2/8-delivered miRNA clusters, allowing potent attenuation of VEGF. These findings may contribute to the development of gene therapy based on AAV-mediated delivery of miRNA clusters.

Toxic response caused by a misfolding variant of the mitochondrial protein short-chain acyl-CoA dehydrogenase

BACKGROUND

Variations in the gene ACADS, encoding the mitochondrial protein short-chain acyl CoA-dehydrogenase (SCAD), have been observed in individuals with clinical symptoms. The phenotype of SCAD deficiency (SCADD) is very heterogeneous, ranging from asymptomatic to severe, without a clear genotype-phenotype correlation, which suggests a multifactorial disorder. The pathophysiological relevance of the genetic variations in the SCAD gene is therefore disputed, and has not yet been elucidated, which is an important step in the investigation of SCADD etiology.

AIM

To determine whether the disease-associated misfolding variant of SCAD protein, p.Arg107Cys, disturbs mitochondrial function.

METHODS

We have developed a cell model system, stably expressing either the SCAD wild-type protein or the misfolding SCAD variant protein, p.Arg107Cys (c.319 C > T). The model system was used for investigation of SCAD with respect to expression, degree of misfolding, and enzymatic SCAD activity. Furthermore, cell proliferation and expression of selected stress response genes were investigated as well as proteomic analysis of mitochondria-enriched extracts in order to study the consequences of p.Arg107Cys protein expression using a global approach.

CONCLUSIONS

We found that expression of the p.Arg107Cys variant SCAD protein gives rise to inactive misfolded protein species, eliciting a mild toxic response manifested though a decreased proliferation rate and oxidative stress, as shown by an increased demand for the mitochondrial antioxidant SOD2. In addition, we found markers of apoptotic activity in the p.Arg107Cys expressing cells, which points to a possible pathophysiological role of this variant protein.

Further immunohistochemical characterization of BRD1 a new susceptibility gene for schizophrenia and bipolar affective disorder

We have recently shown that the gene BRD1 is associated with schizophrenia and bipolar affective disorder and that the BRD1 protein (BRD1) which is expressed in neurons may occur in a short and a long variant. The aim of the study was to generate polyclonal antibodies against new BRD1 epitopes enabling discrimination between the long and short BRD1 variants, and elucidate the BRD1 distribution in several human tissues, including the CNS. Polyclonal rabbit antibodies were raised against three different BRD1 epitopes. One (67) was specific for the long BRD1 variant, whereas the two others (63/64 and 65/66) like the original monoclonal mouse antibody (K22) were predicted to stain both variants. Immunohistochemical staining procedures were subsequently performed on paraffin-embedded human cerebral cortex and microarray slides containing 30 different human tissues. Western blotting confirmed the predicted specificity of the developed antibodies. K22, 63/64 and 65/66 displayed a similar neuronal staining pattern characterized by a distinct but weak nuclear staining, while the surrounding cytoplasm and proximal dendrites were more intensely stained. Interestingly, staining with 67 generated in contrast primarily an intense nuclear staining. The new antibodies resulted, furthermore, in a prominent neuroglial reaction characterized by staining of cell bodies, nuclei and glial processes. The tissue microarray analysis revealed that BRD1 was widely distributed in human tissues. The particular expression profile, e.g., the degree of nuclear and/or cytoplasmatic staining, seemed, however, to be highly tissue dependent. These results suggest a general role of BRD1 in the cell and stress that the two BRD1 variants may play different roles in the etiology of psychiatric disease.

Mitochondrial fatty acid oxidation defects--remaining challenges

Mitochondrial fatty acid oxidation defects have been recognized since the early 1970s. The discovery rate has been rather constant, with 3-4 'new' disorders identified every decade and with the most recent example, ACAD9 deficiency, reported in 2007. In this presentation we will focus on three of the 'old' defects: medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, riboflavin responsive multiple acyl-CoA dehydrogenation (RR-MAD) deficiency, and short-chain acyl-CoA dehydrogenase (SCAD) deficiency. These disorders have been discussed in many publications and at countless conference presentations, and many questions relating to them have been answered. However, continuing clinical and pathophysiological research has raised many further questions, and new ideas and methodologies may be required to answer these. We will discuss these challenges. For MCAD deficiency the key question is why 80% of symptomatic patients are homozygous for the prevalent ACADM gene variation c.985A > G whereas this is found in only approximately 50% of newborns with a positive screen. For RR-MAD deficiency, the challenge is to find the connection between variations in the ETFDH gene and the observed deficiency of a number of different mitochondrial dehydrogenases as well as deficiency of FAD and coenzyme Q(10). With SCAD deficiency, the challenge is to elucidate whether ACADS gene variations are disease-associated, especially when combined with other genetic/cellular/environmental factors, which may act synergistically.

Short-chain acyl-CoA dehydrogenase (SCAD) deficiency: an examination of the medical and neurodevelopmental characteristics of 14 cases identified through newborn screening or clinical symptoms

The medical and neurodevelopmental characteristics of 14 children with short-chain acyl-CoA dehydrogenase deficiency (SCADD) are described. Eight were detected as neonates by newborn screening. Three children diagnosed on the basis of clinical symptoms had normal newborn screening results while three were born in states that did not screen for SCADD. Treatment included frequent feedings and a low fat diet. All children identified by newborn screening demonstrated medical and neuropsychological development within the normative range on follow-up, although one child had a relative weakness in the motor area and another child exhibited mild speech delay. Of the three clinically identified children with newborn screening results below the cut-off value, two were healthy and performed within the normal range on cognitive and motor tests at follow-up. Four clinically identified children with SCADD experienced persistent symptoms and/or developmental delay. However, in each of these cases, there were supplementary or alternative explanations for medical and neuropsychological deficits. Results indicated no genotype-phenotype correlations. These findings suggest that SCADD might be benign and the clinical symptoms ascribed to SCADD reflective of ascertainment bias or that early identification and treatment prevented complications that may have occurred due to interaction between genetic susceptibility and other genetic factors or environmental stressors.

The ACADS gene variation spectrum in 114 patients with short-chain acyl-CoA dehydrogenase (SCAD) deficiency is dominated by missense variations leading to protein misfolding at the cellular level

Short-chain acyl-CoA dehydrogenase (SCAD) deficiency is an inherited disorder of mitochondrial fatty acid oxidation associated with variations in the ACADS gene and variable clinical symptoms. In addition to rare ACADS inactivating variations, two common variations, c.511C > T (p.Arg171Trp) and c.625G > A (p.Gly209Ser), have been identified in patients, but these are also present in up to 14% of normal populations leading to questions of their clinical relevance. The common variant alleles encode proteins with nearly normal enzymatic activity at physiological conditions in vitro. SCAD enzyme function, however, is impaired at increased temperature and the tendency to misfold increases under conditions of cellular stress. The present study examines misfolding of variant SCAD proteins identified in patients with SCAD deficiency. Analysis of the ACADS gene in 114 patients revealed 29 variations, 26 missense, one start codon, and two stop codon variations. In vitro import studies of variant SCAD proteins in isolated mitochondria from SCAD deficient (SCAD-/-) mice demonstrated an increased tendency of the abnormal proteins to misfold and aggregate compared to the wild-type, a phenomenon that often leads to gain-of-function cellular phenotypes. However, no correlation was found between the clinical phenotype and the degree of SCAD dysfunction. We propose that SCAD deficiency should be considered as a disorder of protein folding that can lead to clinical disease in combination with other genetic and environmental factors.