Impact of P2RX7 ablation on the morphological, mechanical and tissue

Duchenne muscular dystrophy (DMD) is an inherited, lethal disorder characterised by progressive muscle degeneration and associated bone abnormalities. We have previously demonstrated that P2RX7 purinergic receptors contribute to the pathogenesis of DMD, and found that P2RX7 ablation alleviated the severity of the disease. In this work we have used a dystrophic mdx mouse crossed with the global P2RX7 receptor to generate a knockout mouse (mdx/P2X7−/−), and compared its morphometric, mechanical and tissue properties against those of mdx, as well as the wild type (WT) and the P2RX7 knockout (P2X7−/-). Micro-computed tomography (µCT), three-point bending testing, scanning electron microscopy (SEM) and nano-indentation were utilised in the study. The bones were analysed at approximately 4 weeks of age to examine the impact of P2RX7 ablation on the bone properties during the acute disease phase, before muscle wasting is fully developed. The results show that P2RX7 purinoceptor ablation has produced improvement or significant improvement in some of the morphological, the mechanical and the tissue properties of the dystrophic bones examined. Specifically, although the ablation produced smaller bones with significantly lower total cross-section area (Tt.Ar) and Second Moment of Area (SMA), significantly higher cortical bone area (Ct.Ar), cortical area fraction (Ct.Ar/Tt.Ar) and trabecular bone volume fraction (BV/TV) are found in the mdx/P2X7−/− mice than in any other types. Further, the mdx/P2X7−/− bones have relatively higher average flexural strength, work-to-fracture and significantly higher strain to failure compared with those of mdx, suggesting greater resistance to fracture. Indentation modulus, elasticity and creep are also significantly improved in the knockout cortical bones over those of mdx. These findings seem to suggest that specific pharmacological blockade of P2RX7 may improve dystrophic bones, with a potential for therapeutic application in the treatment of the disease

P2RX7 Purinoceptor: A Therapeutic Target for Ameliorating the Symptoms of Duchenne Muscular Dystrophy

open access articleDuchenne muscular dystrophy (DMD) is the most common inherited muscle disease, leading to severe disability and death in young men. Death is caused by the progressive degeneration of striated muscles aggravated by sterile inflammation. The pleiotropic effects of the mutant gene also include cognitive and behavioral impairments and low bone density. Current interventions in DMD are palliative only as no treatment improves the long-term outcome. Therefore, approaches with a translational potential should be investigated, and key abnormalities downstream from the absence of the DMD product, dystrophin, appear to be strong therapeutic targets. We and others have demonstrated that DMD mutations alter ATP signaling and have identified P2RX7 purinoceptor up-regulation as being responsible for the death of muscles in the mdx mouse model of DMD and human DMD lymphoblasts. Moreover, the ATP–P2RX7 axis, being a crucial activator of innate immune responses, can contribute to DMD pathology by stimulating chronic inflammation. We investigated whether ablation of P2RX7 attenuates the DMD model mouse phenotype to assess receptor suitability as a therapeutic target

Live axonal transport disruption by mutant huntingtin fragments in Drosophila motor neuron axons

Huntington's Disease is a neurodegenerative condition caused by a polyglutamine expansion in thehuntingtin (Htt) protein, which aggregates and also causes neuronal dysfunction. Pathogenic N-terminal httfragments perturb axonal transport in vitro. To determine whether this occurs in vivo and to elucidate howtransport is affected, we expressed htt exon 1 with either pathogenic (HttEx1Q93) or non-pathogenic (HttEx1Q20) polyglutamine tracts in Drosophila. We found that HttEx1Q93 expression causes axonalaccumulation of GFP-tagged fast axonal transport vesicles in vivo and leads to aggregates within larval motorneuron axons. Time-lapse video microscopy, shows that vesicle velocity is unchanged in HttEx1Q93-axonscompared to HttEx1Q20-axons, but vesicle stalling occurs to a greater extent. Whilst HttEx1Q93 expressiondid not affect locomotor behaviour, external heat stress unveiled a locomotion deficit in HttEx1Q93 larvae.Therefore vesicle transport abnormalities amidst axonal htt aggregation places a cumulative burden uponnormal neuronal function under stressful conditions

Live axonal transport disruption by mutant huntingtin fragments in Drosophila motor neuron axons.

Huntington's Disease is a neurodegenerative condition caused by a polyglutamine expansion in the huntingtin (Htt) protein, which aggregates and also causes neuronal dysfunction. Pathogenic N-terminal htt fragments perturb axonal transport in vitro. To determine whether this occurs in vivo and to elucidate how transport is affected, we expressed htt exon 1 with either pathogenic (HttEx1Q93) or non-pathogenic (HttEx1Q20) polyglutamine tracts in Drosophila. We found that HttEx1Q93 expression causes axonal accumulation of GFP-tagged fast axonal transport vesicles in vivo and leads to aggregates within larval motor neuron axons. Time-lapse video microscopy, shows that vesicle velocity is unchanged in HttEx1Q93-axons compared to HttEx1Q20-axons, but vesicle stalling occurs to a greater extent. Whilst HttEx1Q93 expression did not affect locomotor behaviour, external heat stress unveiled a locomotion deficit in HttEx1Q93 larvae. Therefore vesicle transport abnormalities amidst axonal htt aggregation places a cumulative burden upon normal neuronal function under stressful conditions