Improvement of spinal muscular atrophy via correction of the SMN2 splicing defect by Brucea javanica (L.) Merr. extract and Bruceine D

Phytomedicine. 2019 Dec:65:153089. doi: 10.1016/j.phymed.2019.153089. Epub 2019 Sep 16.

Abstract

Background: Spinal muscular atrophy (SMA) is a rare neuromuscular disease and a leading genetic cause of infant mortality. SMA is caused primarily by the deletion of the survival motor neuron 1 (SMN1) gene, which leaves the duplicate gene SMN2 as the sole source of SMN protein. The splicing defect (exon 7 skipping) of SMN2 leads to an insufficient amount of SMN protein. Therefore, correcting this SMN2 splicing defect is considered to be a promising approach for the treatment of SMA.

Purpose: This study aimed to identify active compounds and extracts from plant resources to rescue SMA phenotypes through the correction of SMN2 splicing.

Study design: Of available plant resources, candidates with SMA-related traditional medicine information were selected for screening using a robust luciferase-based SMN2 splicing reporter. Primary hits were further evaluated for their ability to correct the splicing defect and resultant increase of SMN activity in SMA patient-derived fibroblasts. Confirmed hits were finally tested to determine the beneficial effects on the severe Δ7 SMA mouse.

Methods: SMN2 splicing was analyzed using a luciferase-based SMN2 splicing reporter and subsequent RT-PCR of SMN2 mRNAs. SMA phenotypes were evaluated by the survival, body weights, and righting reflex of Δ7 SMA mice.

Results: In a screen of 492 selected plant extracts, we found that Brucea javanica extract and its major constituent Bruceine D have SMN2 splicing-correcting activity. Their ability to correct the splicing defect and the resulting increased SMN activity were further confirmed in SMA fibroblasts. Importantly, both B. javanica and Bruceine D noticeably improved the phenotypic defects, especially muscle function, in SMA mice. Reduced expression of heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) contributed to the correction of splicing by B. javanica.

Conclusion: Our work revealed that B. javanica and Bruceine D correct the SMN2 splicing defect and improve the symptoms of SMA in mice. These resources will provide another possibility for development of a plant-derived SMA drug candidate.

Keywords: Alternative splicing; Brucea javanica, Bruceine D; Neuromuscular disease; Spinal muscular atrophy (SMA); Splicing modulator.

MeSH terms

  • Alternative Splicing
  • Animals
  • Brucea / chemistry*
  • Cell Line
  • Disease Models, Animal
  • Drug Evaluation, Preclinical / methods
  • Exons
  • Humans
  • Mice, Transgenic
  • Muscular Atrophy, Spinal / drug therapy*
  • Muscular Atrophy, Spinal / genetics
  • Plant Extracts / chemistry
  • Plant Extracts / pharmacology*
  • Quassins / pharmacology*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Survival of Motor Neuron 2 Protein / genetics

Substances

  • Plant Extracts
  • Quassins
  • RNA, Messenger
  • SMN2 protein, human
  • Survival of Motor Neuron 2 Protein
  • bruceine D