Accelerated loss of hypoxia response in zebrafish with familial Alzheimer's disease-like mutation of presenilin 1.

Ageing is the major risk factor for Alzheimer's disease (AD), a condition involving brain hypoxia. The majority of early-onset familial AD (EOfAD) cases involve dominant mutations in the gene PSEN1. PSEN1 null mutations do not cause EOfAD. We exploited putative hypomorphic and EOfAD-like mutations in the zebrafish psen1 gene to explore the effects of age and genotype on brain responses to acute hypoxia. Both mutations accelerate age-dependent changes in hypoxia-sensitive gene expression supporting that ageing is necessary, but insufficient, for AD occurrence. Curiously, the responses to acute hypoxia become inverted in extremely aged fish. This is associated with an apparent inability to upregulate glycolysis. Wild-type PSEN1 allele expression is reduced in post-mortem brains of human EOfAD mutation carriers (and extremely aged fish), possibly contributing to EOfAD pathogenesis. We also observed that age-dependent loss of HIF1 stabilization under hypoxia is a phenomenon conserved across vertebrate classes.

Condensation-Driven Chondrogenesis of Human Mesenchymal Stem Cells within Their Own Extracellular Matrix: Formation of Cartilage with Low Hypertrophy and Physiologically Relevant Mechanical Properties.

Mesenchymal stem cells (MSCs) represent a promising cell source to regenerate injured cartilage. In this study, MSCs are cultured under confluent conditions for 10 days to optimize the deposition of the extracellular matrix (mECM), which will serve as the scaffold to support MSC chondrogenesis. Subsequently, the MSC-impregnated mECM (MSC-mECM) composite is briefly treated with trypsin, allowing the MSCs to adopt a round morphology without being detached from their own mECM. The constructs are then cultured in a chondrogenic medium. Interestingly, after trypsin removal, the treated MSCs undergo an aggregation process, mimicking mesenchymal condensation during developmental chondrogenesis, specifically indicated by peanut agglutinin staining and immunodetectable N-cadherin expression, followed by robust chondrogenic differentiation. In comparison to conventional pellet culture, chondrogenically induced MSC-mECM displays a similar level of chondrogenesis, but with significantly reduced hypertrophy. The reparative capacity of the MSC-mECM derived construct is assessed using bovine cartilage explants. Mechanical testing and histology results show that engineered cartilage from MSC-mECM forms better integration with the surrounding native cartilage tissue and displays a much lower hypertrophic differentiation than that from pellet culture. Taken together, these findings demonstrate that MSC-mECM may be an efficacious stem cell-based product for the repair of hyaline cartilage injury without the use of exogenous scaffolds.

Motor Neuron Abnormalities Correlate with Impaired Movement in Zebrafish that Express Mutant Superoxide Dismutase 1.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive loss of motor neurons. ALS can be modeled in zebrafish (Danio rerio) through the expression of human ALS-causing genes, such as superoxide dismutase 1 (SOD1). Overexpression of mutated human SOD1 protein causes aberrant branching and shortening of spinal motor axons. Despite this, the functional relevance of this axon morphology remains elusive. Our aim was to determine whether this motor axonopathy is correlated with impaired movement in mutant (MT) SOD1-expressing zebrafish. Transgenic zebrafish embryos that express blue fluorescent protein (mTagBFP) in motor neurons were injected with either wild-type (WT) or MT (A4V) human SOD1 messenger ribonucleic acid (mRNA). At 48 hours post-fertilization, larvae movement (distance traveled during behavioral testing) was examined, followed by quantification of motor axon length. Larvae injected with MT SOD1 mRNA had significantly shorter and more aberrantly branched motor axons (p < 0.002) and traveled a significantly shorter distance during behavioral testing (p < 0.001) when compared with WT SOD1 and noninjected larvae. Furthermore, there was a positive correlation between distance traveled and motor axon length (R2 = 0.357, p < 0.001). These data represent the first correlative investigation of motor axonopathies and impaired movement in SOD1-expressing zebrafish, confirming functional relevance and validating movement as a disease phenotype for the testing of disease treatments for ALS.