Combination of valproic acid and morpholino splice-switching oligonucleotide produces improved outcomes in spinal muscular atrophy patient-derived fibroblasts.

Spinal muscular atrophy (SMA), the leading genetic cause of infant mortality worldwide, is characterised by the homozygous loss of the survival motor neuron 1 (SMN1) gene. The consequent degeneration of spinal motor neurons and progressive atrophy of voluntary muscle groups results in paralysis and eventually premature infantile death. Humans possess a second nearly identical copy of SMN1, known as SMN2. However, SMN2 produces only 10-20% functional SMN protein due to aberrant splicing of its pre-mRNA that leads to the exclusion of exon 7. This level of SMN is insufficient to rescue the phenotype. Recently developed splice-switching antisense oligonuclotides (SSO) have shown great promise in correcting the aberrant splicing of SMN2 towards producing functional SMN protein. Several FDA approved drugs are being repurposed for SMA treatment including valproic acid (VPA), a histone deacetylase inhibitor, which has been shown to increase overall SMN2 expression. In this study, we have characterised the effects of single and combined treatment of VPA and a SSO based on phosphorodiamidate morpholino oligomer (PMO) chemistry. We conjugated both VPA and PMO to a single cell-penetrating peptide (Apolipoprotein E (ApoE)) for their simultaneous intracellular delivery. Treatment of SMA Type I patient-derived fibroblasts with the conjugates showed no additive increase in the level of full-length SMN2 mRNA expression over both 4 and 16 h treatments indicating that conjugation of VPA to ApoE-PMO has limited benefit. However, treatment with a combination of VPA and ApoE-PMO induced more favourable splice switching activity than either agent alone, promoting exon 7 inclusion in SMN2 transcripts. Our results suggest that combination therapy of VPA and ApoE-PMO is superior in upregulating SMN2 production in vitro, as compared to singular treatment of each compound at both transcriptional and protein levels. This study provides the first indication of a novel dual therapy approach for the potential treatment of SMA.

Silent information regulator 1 modulator resveratrol increases brain lactate production and inhibits mitochondrial metabolism, whereas SRT1720 increases oxidative metabolism.

Silent information regulators (SIRTs) have been shown to deacetylate a range of metabolic enzymes, including those in glycolysis and the Krebs cycle, and thus alter their activity. SIRTs require NAD(+) for their activity, linking cellular energy status to enzyme activity. To examine the impact of SIRT1 modulation on oxidative metabolism, this study tests the effect of ligands that are either SIRT-activating compounds (resveratrol and SRT1720) or SIRT inhibitors (EX527) on the metabolism of (13)C-enriched substrates by guinea pig brain cortical tissue slices with (13)C and (1)H nuclear magnetic resonance spectroscopy. Resveratrol increased lactate labeling but decreased incorporation of (13)C into Krebs cycle intermediates, consistent with effects on AMPK and inhibition of the F0/F1-ATPase. By testing with resveratrol that was directly applied to astrocytes with a Seahorse analyzer, increased glycolytic shift and increased mitochondrial proton leak resulting from interactions of resveratrol with the mitochondrial electron transport chain were revealed. SRT1720, by contrast, stimulated incorporation of (13)C into Krebs cycle intermediates and reduced incorporation into lactate, although the inhibitor EX527 paradoxically also increased Krebs cycle (13)C incorporation. In summary, the various SIRT1 modulators show distinct acute effects on oxidative metabolism. The strong effects of resveratrol on the mitochondrial respiratory chain and on glycolysis suggest that caution should be used in attempts to increase bioavailability of this compound in the CNS.

Rif-mDia1 interaction is involved in filopodium formation independent of Cdc42 and Rac effectors.

Filopodia are cellular protrusions important for axon guidance, embryonic development, and wound healing. The Rho GTPase Cdc42 is the best studied inducer of filopodium formation, and several of its effectors and their interacting partners have been linked to the process. These include IRSp53, N-WASP, Mena, and Eps8. The Rho GTPase, Rif, also drives filopodium formation. The signaling pathway by which Rif induces filopodia is poorly understood, with mDia2 being the only protein implicated to date. It is thus not clear how distinct the Rif-driven pathway for filopodium formation is from the one mediated by Cdc42. In this study, we characterize the dynamics of Rif-induced filopodia by time lapse imaging of live neuronal cells and show that Rif drives filopodium formation via an independent pathway that does not involve the Cdc42 effectors N-WASP and IRSp53, the IRSp53 binding partner Mena, or the Rac effectors WAVE1 and WAVE2. Rif formed filopodia in the absence of N-WASP or Mena and when IRSp53, WAVE1, or WAVE2 was knocked down by RNAi. Rif-mediated filopodial protrusion was instead reduced by silencing mDia1 expression or overexpressing a dominant negative mutant of mDia1. mDia1 on its own was able to form filopodia. Data from acceptor photobleaching FRET studies of protein-protein interaction demonstrate that Rif interacts directly with mDia1 in filopodia but not with mDia2. Taken together, these results suggest a novel pathway for filopodia formation via Rif and mDia1.