Astrocyte SMN Restoration and Forskolin Treatment Improve SMA Synaptic Pathology.
Abstract
Objective
Early phenotypic presentation of central afferent synapse dysfunction within patients with spinal muscular atrophy (SMA) represents a key target for therapeutic development; however, the underlying disease mechanisms remain unresolved. By further investigating motor neuron synapse and peri-synaptic astrocyte process (PAP) defects in human SMA disease pathology, we aimed to develop a novel therapeutic approach to improve motor neuron function.
Methods
We utilized healthy subjects and patients with SMA induced pluripotent stem cell (iPSC)-derived cultures to assess phenotypes occurring intrinsically within astrocyte processes (monocultures) and at the PAP-synaptic interface (co-cultures), respectively, using cell surface capture mass spectrometry proteomics, confocal and super resolution microscopy, synaptogliosome (SG) isolation, and electrophysiology.
Results
SMA astrocytes demonstrated intrinsic filopodia actin defects featuring low abundance of actin-associated cell surface N-glycoproteins, decreased filopodia density and CDC42-GTP levels after actin remodeling stimulation, and significantly reduced phosphorylated ezrin, radixin, and moesin (pERM) proteins. Within the SMA motor neuron and astrocyte co-cultures, we observed concurrent decreases in synapse number, actin-associated synapsin I expression, and PAP-associated expression of pERM proteins. Our dual treatment paradigm using SMN1 gene therapy combined with forskolin treatment to stimulate actin dynamics via increasing cyclic adenosine monophosphate levels resulted in increased branching and filopodia density of SMA astrocytes, and improved synapse formation and function of SMA motor neurons.
Interpretation
We define actin-associated defects impacting astrocyte filopodia dynamics and motor neuron synaptic function in SMA. This shaped our therapeutic approach targeted to SMN-dependent and actin-related disease mechanisms, which overall demonstrated improvements in motor neuron function and disease pathology. ANN NEUROL 2026.