Biology subjects

Sweeney, L.

Publications and source records attributed to Sweeney, L..

4 recordsLinked to original sources

bioRxiv2022

Potential limitations of micro-dystrophin gene therapy for Duchenne muscular dystrophy

Adeno-associated viruses (AAVs) expressing versions of truncated dystrophin (micro-dystrophins) are being delivered at high doses to patients with Duchenne muscular dystrophy (DMD) in clinical trials. We examined this strategy with two different micro-dystrophins, similar to those currently in clinical trials, in a severe mouse model of DMD, the D2.mdx mouse, using doses of AAV comparable to those used in the clinical trials. We achieved high levels of micro-dystrophin expression in striated muscle with cardiac expression [~]10 fold higher than that observed in skeletal muscle. Significant, albeit incomplete, correction of the skeletal muscle disease is observed. Surprisingly, a lethal acceleration of cardiac disease progression occurs with one of the micro-dystrophins, while the second appears to benefit the heart. The detrimental impact on the heart in the first case appears to be caused by the high levels of micro-dystrophin in the heart resulting in competition between micro-dystrophin and utrophin at the cardiomyocyte membrane. While the significance of these observations for patients currently being treated with AAV-micro-dystrophin therapies is unclear since the levels of expression being achieved in the DMD hearts are unknown, it suggests that micro-dystrophin treatments may need to be carefully titrated to avoid high levels of expression in the heart.

pharmacology and toxicology↗

bioRxiv2022

Postsynaptic receptors regulate presynaptic neurotransmitter stability

Stable matching of neurotransmitters with their receptors is fundamental to synapse function, to achieve reliable and robust communication in neural circuits. Presynaptic neurotransmitters regulate selection of postsynaptic transmitter receptors. However, whether postsynaptic receptors regulate selection of presynaptic transmitters is unknown. Here we show that blockade of postsynaptic acetylcholine receptors at the neuromuscular junction leads to loss of the cholinergic phenotype in motor neurons and stabilization of an earlier, developmentally transient glutamatergic phenotype. Exogenous postsynaptic expression of GABAA receptors leads to the stabilization of an earlier, developmentally transient GABAergic motor neuron phenotype. Both acetylcholine receptors and GABA receptors are linked to presynaptic neurons through trans-synaptic bridges. Knock-down of different components of these trans-synaptic bridges prevents stabilization of the cholinergic and GABAergic phenotypes. We conclude that this bidirectional communication enforces a match between transmitter and receptor and ensures the fidelity of synaptic transmission. Our findings suggest a role of dysfunctional transmitter receptors in neurological disorders that involve the loss of the presynaptic transmitter.

neuroscience↗

bioRxiv2021

High-resolution structures of the actomyosin-V complex in three nucleotide states provide insights into the force generation mechanism

The molecular motor myosin undergoes a series of major structural transitions during its force-producing motor cycle. The underlying mechanism and its coupling to ATP hydrolysis and actin binding is only partially understood, mostly due to sparse structural data on actin-bound states of myosin. Here, we report 26 high-resolution cryo-EM structures of the actomyosin-V complex in the strong-ADP, rigor, and a previously unseen post-rigor transition state that binds the ATP analog AppNHp. The structures reveal a high flexibility of myosin in each state and provide valuable insights into the structural transitions of myosin-V upon ADP release and binding of AppNHp, as well as the actomyosin interface. In addition, they show how myosin is able to specifically alter the structure of F-actin. The unprecedented number of high-resolution structures of a single myosin finally enabled us to assemble a nearly complete structural model of the myosin-V motor cycle and describe the molecular principles of force production.

biochemistry↗

bioRxiv2021

Filopodia powered by class X myosin promote fusion of mammalian myoblasts

Skeletal muscle fibers are multinucleated cellular giants formed by the fusion of mononuclear myoblasts. Several molecules involved in myoblast fusion have been discovered, and finger-like projections coincident with myoblast fusion have also been implicated in the fusion process. The role of these cellular projections in muscle cell fusion was investigated herein. We demonstrate that these projections are filopodia generated by class X myosin (Myo10), an unconventional myosin motor protein specialized for filopodia. We further show that Myo10 is highly expressed by differentiating myoblasts, and Myo10 ablation inhibits both filopodia formation and myoblast fusion in vitro. In vivo, Myo10 labels regenerating muscle fibers associated with Duchenne muscular dystrophy and acute muscle injury. Conditional loss of Myo10 from muscle-resident stem cells, known as satellite cells, severely impairs postnatal muscle regeneration. Furthermore, the muscle fusion proteins Myomaker and Myomixer are detected in myoblast filopodia. These data demonstrate that Myo10-driven filopodia facilitate multi-nucleated mammalian muscle formation.

cell biology↗