Neuroprotective effects of mesenchymal stem cells on spinal motoneurons following ventral root axotomy: synapse stability and axonal regeneration

Abstract

Compression of spinal roots is an important medical problem, which may arise from intervertebral disc herniation, tumor growth or as a result of high energy accidents. Differently from avulsion, root crushing maintains the central/peripheral nervous system (CNS/PNS) connection, although the axons are axotomized and motoneurons degenerate. Such neuronal death may decrease and delay motor function recovery. In the present study we have investigated the neuroprotective effects of mesenchymal stem cell (MSC) therapy following such proximal lesions. Motor recovery and synaptic stabilization were analyzed by the use of morphological and functional approaches. For that, crushing the ventral roots at L4, L5 and L6 was unilaterally performed in Lewis rats. Four weeks after injury, an increased motoneuron survival was observed in the MSC-treated group, coupled with a smaller decrease of inputs at the motoneuron surface and nearby neuropil, seen by synaptophysin and synapsin immunolabeling and decreased astrogliosis, seen by GFAP immunolabeling. In this sense, MSC-treated group displayed a significant preservation of GABAergic terminals, indicating a possible neuroprotection to glutamate excitotoxicity. Motor function recovery was acutely improved in MSC-treated group as compared to Dulbeco's modified eagle medium (DMEM)-treated. Overall, we provide evidence that ventral root crushing (VRC), although milder than avulsion, results in significant loss of motoneurons (~51%) that can be reduced by MSC administration within the spinal cord. Such treatment also improves the number of synapses immunoreactive against molecules present in inhibitory inputs. Also, an increased number of regenerated axons was obtained in the MSC-treated group, in comparison to the DMEM-treated control. Overall, MSC therapy acutely improved limb strength and gait coordination, indicating a possible clinical application of such treatment following proximal lesions at the CNS/PNS interface.

Keywords: BDNF; CL; DMEM; Dulbeco’s modified eagle medium; EGFP; IL; MSC; PB; PBS; PNS; VRA; VRC; brain-derived neurotrophic factor; contralateral side to lesion; enhanced green fluorescent protein; functional recovery; ipsilateral side to lesion; mesenchymal stem cells; peripheral nervous system; phosphate buffer; phosphate-buffered saline; regeneration; stem cells; synaptic plasticity; ventral root avulsion; ventral root crushing.