R-Roscovitine Improves Motoneuron Function in Mouse Models for Spinal Muscular Atrophy

Abstract

Neurotransmission defects and motoneuron degeneration are hallmarks of spinal muscular atrophy, a monogenetic disease caused by the deficiency of the SMN protein. In the present study, we show that systemic application of R-Roscovitine, a Ca v 2.1/Ca v 2.2 channel modifier and a cyclin-dependent kinase 5 (Cdk-5) inhibitor, significantly improved survival of SMA mice. In addition, R-Roscovitine increased Ca v 2.1 channel density and sizes of the motor endplates. In vitro, R-Roscovitine restored axon lengths and growth cone sizes of Smn-deficient motoneurons corresponding to enhanced spontaneous Ca 2+ influx and elevated Ca v 2.2 channel cluster formations independent of its capability to inhibit Cdk-5. Acute application of R-Roscovitine at the neuromuscular junction significantly increased evoked neurotransmitter release, increased the frequency of spontaneous miniature potentials, and lowered the activation threshold of silent terminals. These data indicate that R-Roscovitine improves Ca 2+ signaling and Ca 2+ homeostasis in Smn-deficient motoneurons, which is generally crucial for motoneuron differentiation, maturation, and function.

The Mouse Levator Auris Longus Muscle: An Amenable Model System to Study the Role of Postsynaptic Proteins to the Maintenance and Regeneration of the Neuromuscular Synapse

“…Muscle contraction was prevented by including in the bath 3–4 mM μ-conotoxin GIIIB (Alomone Laboratories, Jerusalem, Israel), a specific blocker of muscular voltage-gated sodium channels. The data were analyzed as previously described (Tejero et al, 2016 , 2020 ). EPP amplitudes were normalized to −70 mV and corrected for nonlinear summation.…”

In Search of a Cure: The Development of Therapeutics to Alter the Progression of Spinal Muscular Atrophy

“…The effects of BDNF have also been explored in developing motoneuron cultures and SMA models. Through its mechanism of action on TrkB receptors, BDNF application augments calcium transients via increased Cav2.2 clustering, and improves F-actin assembly and growth cone formation in motoneurons in vitro [ 252 ], suggesting that some of the developmental defects seen in SMA model cultured motoneurons [ 145 ] and mice [ 253 ] are consequences of reduced BDNF-mediated trophic support. SMN-regulated BDNF expression has also been explored in SMA model NSC-34 motoneuron-like cells.…”

“…One recent investigation by Tejero et al (2020) [ 253 ] investigated the effect of ( R )-Roscovitine, a cdk-5 inhibitor with positive allosteric effects on voltage-gated calcium channels (Cav2.1-Cav2.2), on SMA pathology during motoneuron development. Application of ( R )-Roscovitine to SMA motoneuron cultures increased Cav2.2 channel clustering, spontaneous calcium transients, elongated axons, and improved neurotransmission [ 253 ].…”

“…One recent investigation by Tejero et al (2020) [ 253 ] investigated the effect of ( R )-Roscovitine, a cdk-5 inhibitor with positive allosteric effects on voltage-gated calcium channels (Cav2.1-Cav2.2), on SMA pathology during motoneuron development. Application of ( R )-Roscovitine to SMA motoneuron cultures increased Cav2.2 channel clustering, spontaneous calcium transients, elongated axons, and improved neurotransmission [ 253 ]. Axonal elongation was similar when motoneuron cultures were exposed to a derivative of ( R )-Roscovitine, GV-58, which is a molecule with more potent Cav2.1-2.2 effects and no significant cdk activity at physiological ATP levels [ 277 ].…”

Drug Screening and Drug Repositioning as Promising Therapeutic Approaches for Spinal Muscular Atrophy Treatment

“…The most used SMA murine model for DS/DR is certainly the SMNΔ7 mouse: it is a triple homozygote, characterized by selective spinal MN degeneration, progressive muscle atrophy, reduced body weight, early (from postnatal day 5, P5) motor performance impairment, and premature death (around P14) compared to WT littermates (Edens et al, 2015;Simon et al, 2017;Kannan et al, 2018;Rimer et al, 2019;Tejero et al, 2020). The other available SMA models are generally excluded from DS/ DR studies, since they die too early (by P5, or even embryonic, respectively in the case of FVB.SMN2;Smn − and SMN − ) or too late [Smn A2G and Smn1 c , and FVB.…”