Glial activation and central synapse loss, but not motoneuron degeneration, are prevented by the sigma-1 receptor agonist pre-084 in the SMN2B/ mouse model of spinal muscular atrophy

Abstract

Spinal muscular atrophy (SMA) is characterized by the loss of a-motoneurons (MNs) with concomitant muscle denervation. MN excitability and vulnerability to disease are particularly regulated by cholinergic synaptic afferents (C-boutons), in which Sigma-1 receptor (Sig1R) is concentrated. Alterations in Sig1R have been associated with MN degeneration. Here, we investigated whether a chronic treatment with the Sig1R agonist PRE-084 was able to exert beneficial effects on SMA. We used a model of intermediate SMA, the Smn2B/ mouse, in which we performed a detailed characterization of the histopathological changes that occur throughout the disease. We report that Smn2B/ mice exhibited qualitative differences in major alterations found in mouse models of severe SMA: Smn2B/ animals showed more prominent MN degeneration, early motor axon alterations, marked changes in sensory neurons, and later MN deafferentation that correlated with conspicuous reactive gliosis and altered neuroinflammatory M1/M2 microglial balance. PRE-084 attenuated reactive gliosis, mitigated M1/M2 imbalance, and prevented MN deafferentation in Smn2B/ mice. These effects were also observed in a severe SMA model, the SMND7 mouse. However, the prevention of gliosis and MN deafferentation promoted by PRE-084 were not accompanied by any improvements in clinical outcome or other major pathological changes found in SMA mice.