Epilepsy-causing sequence variations in SIK1 disrupt synaptic activity response gene expression and affect neuronal morphology.

SIK1 syndrome is a newly described developmental epilepsy disorder caused by heterozygous mutations in the salt-inducible kinase SIK1. To better understand the pathophysiology of SIK1 syndrome, we studied the effects of SIK1 pathogenic sequence variations in human neurons. Primary human fetal cortical neurons were transfected with a lentiviral vector to overexpress wild-type and mutant SIK1 protein. We evaluated the transcriptional activity of known downstream gene targets in neurons expressing mutant SIK1 compared with wild type. We then assayed neuronal morphology by measuring neurite length, number and branching. Truncating SIK1 sequence variations were associated with abnormal MEF2C transcriptional activity and decreased MEF2C protein levels. Epilepsy-causing SIK1 sequence variations were associated with significantly decreased expression of ARC (activity-regulated cytoskeletal-associated) and other synaptic activity response element genes. Assay of mRNA levels for other MEF2C target genes NR4A1 (Nur77) and NRG1, found significantly, decreased the expression of these genes as well. The missense p.(Pro287Thr) SIK1 sequence variation was associated with abnormal neuronal morphology, with significant decreases in mean neurite length, mean number of neurites and a significant increase in proximal branches compared with wild type. Epilepsy-causing SIK1 sequence variations resulted in abnormalities in the MEF2C-ARC pathway of neuronal development and synapse activity response. This work provides the first insights into the mechanisms of pathogenesis in SIK1 syndrome, and extends the ARX-MEF2C pathway in the pathogenesis of developmental epilepsy.

Astroglial-derived periostin promotes axonal regeneration after spinal cord injury.

Traumatic spinal cord injury (SCI) results in a cascade of tissue responses leading to cell death, axonal degeneration, and glial scar formation, exacerbating the already hostile environment and further inhibiting axon regeneration. Overcoming these inhibitory cues and promoting axonal regeneration is one of the primary targets in developing a cure for SCI. Previously, we demonstrated that transplantation of bone morphogenetic protein (BMP)-induced astrocytes derived from embryonic glial-restricted precursors (GDAs(BMP)) promotes extensive axonal growth and motor function recovery in a rodent spinal cord injury model. Here, we identify periostin (POSTN), a secreted protein, as a key component of GDA(BMP)-induced axonal regeneration. POSTN is highly expressed by GDAs(BMP) and the perturbation of POSTN expression by shRNA diminished GDA(BMP)-induced neurite extension in vitro. We also found that recombinant POSTN is sufficient to overcome the inhibitory effect of scar-associated molecules and promote neurite extension in vitro by signaling through focal adhesion kinase and Akt. Furthermore, transplantation of POSTN-deficient GDAs(BMP) into the injured rat spinal cord resulted in compromised axonal regeneration, indicating that POSTN plays an essential role in GDA(BMP)-mediated axonal regeneration. This finding reveals not only one of the major mechanisms underlying GDA(BMP)-dependent recovery from SCI, but also the potential of POSTN as a therapeutic agent for traumatic injury of the CNS.

EIF2B5 mutations compromise GFAP+ astrocyte generation in vanishing white matter leukodystrophy.

Vanishing white matter disease (VWM) is a heritable leukodystrophy linked to mutations in translation initiation factor 2B (eIF2B). Although the clinical course of this disease has been relatively well described, the cellular consequences of EIF2B mutations on neural cells are unknown. Here we have established cell cultures from the brain of an individual with VWM carrying mutations in subunit 5 of eIF2B (encoded by EIF2B5). Despite the extensive demyelination apparent in this VWM patient, normal-appearing oligodendrocytes were readily generated in vitro. In contrast, few GFAP-expressing (GFAP+) astrocytes were present in primary cultures, induction of astrocytes was severely compromised, and the few astrocytes generated showed abnormal morphologies and antigenic phenotypes. Lesions in vivo also lacked GFAP+ astrocytes. RNAi targeting of EIF2B5 severely compromised the induction of GFAP+ cells from normal human glial progenitors. This raises the possibility that a deficiency in astrocyte function may contribute to the loss of white matter in VWM leukodystrophy.