Triplet, Erin M.

ABSTRACT Disruptions in the metabolism of cholesterol and other lipids are strongly implicated in the pathogenesis of neurological disease. The CNS is highly enriched in cholesterol, which is primarily synthesized de novo . Cholesterol synthesis is also rate limiting for myelin regeneration. Given that knockout of the thrombin receptor (Protease Activated Receptor 1 (PAR1)) accelerates myelin regeneration, here we sought to determine the potential regulatory actions of PAR1 in CNS cholesterol and lipid metabolism in the intact adult CNS and during myelin regeneration. We present quantitative PCR and RNAseq evidence from murine spinal cords at the peak of myelination and in adulthood showing PAR1 knockout is associated with increased gene expression for cholesterol biosynthesis (Hmgcs1, Hmgcr, Sqle, and Dhcr7), lipid transport (ApoE, Abca1, and Ldlr), and intracellular processing (Lcat, Npc1, and Npc2) at one or more time points examined. An upregulation of genes involved in the synthesis of other lipids enriched in the myelin membrane, specifically Fa2h, Ugt8a, and Gal3st1, was also observed in PAR1 knockouts. Transcription factors essential for lipid and cholesterol production (Srebf1 and Srebf2) were also increased in PAR1 knockout spinal cords at the postnatal day 21 peak of myelination and at day 45. GC–MS and LC–MS quantification of lipids demonstrated coordinate increases in the abundance of select cholesterol and lipid species in the spinal cords of PAR1 knockout mice, including enrichment of esterified cholesterol, together with sphingomyelins and sphingolipids. Co‐localization of the SREBP1 and SREBP2 transcription factors, as well as HMGCS1, a rate‐limiting enzyme in cholesterol biosynthesis, to glia during remyelination post‐lysolecithin or cuprizone‐mediated demyelination showed a prominent regulatory role for PAR1 in Olig2+ oligodendrocytes. PAR1 knockouts also demonstrated elevated levels of SREBP2 in more mature GST3+ oligodendrocytes and SREBP1 in GFAP+ astrocytes during remyelination post‐lysolecithin. These findings demonstrate novel roles for PAR1 as a regulator of CNS cholesterol and lipid metabolism and its potential as a therapeutic target to increase cholesterol availability to improve myelin regeneration. image

AbstractObjectiveInfants with focal‐onset epilepsy are an understudied population, requiring additional evaluation for clinical assessment and prognostication. Our goal was to characterize the etiology and natural history of infantile‐onset focal epilepsy.MethodsWe retrospectively identified all infants (0–24 months) with onset of focal epilepsy while resident in Olmsted County, Minnesota, between 1980 and 2018, using the Rochester Epidemiology Project Database. We assessed the impact of etiology on both seizure and neurodevelopmental outcome, and mortality.ResultsOf 686 children with epilepsy onset <18 years, 125 (18.2%) presented with focal‐onset seizures in infancy. Median follow‐up for this group was 10.9 years (interquartile range [IQR] 6.2, 19.3). Etiology was identified in 65.6% (structural N = 62, genetic N = 13, both structural and genetic N = 3, metabolic N = 4). Of 107 patients followed >2 years, 38 (35.5%) developed drug‐resistant epilepsy (DRE). DRE was more likely with younger age at onset, known etiology, and presence of epileptic spasms. Sixty‐eight (63.0% of those with follow‐up) were developmentally delayed at last follow‐up, and known etiology, DRE, and presence of epileptic spasms were significantly associated with delay (p < .001 for all). Fifteen patients (12.0%) died at a median age of 7.1 years (IQR 1.7, 21.7), but only one death was seizure related (suspected sudden unexpected death in epilepsy [SUDEP]). Of 20 infants with normal development at onset and no known etiology with >2 years follow‐up, none developed DRE, all were seizure‐free at last follow‐up (95% off antiseizure medications [ASMs]), and all remained developmentally normal.SignificanceInfantile‐onset focal epilepsy accounts for 18% of all epilepsy in childhood, is frequently due to known etiologies, and has a high rate of DRE. However, developmentally normal infants without a known cause appear to have a very favorable course.

AbstractKallikrein related peptidase 6 (Klk6) is a secreted serine protease highly expressed in oligodendrocytes and implicated in demyelinating conditions. To gain insights into the significance of Klk6 to oligodendrocyte biology, we investigated the impact of global Klk6 gene knockout on CNS developmental myelination using the spinal cord of male and female mice as a model. Results demonstrate that constitutive loss of Klk6 expression accelerates oligodendrocyte differentiation developmentally, including increases in the expression of myelin proteins such as MBP, PLP and CNPase, in the number of CC‐1+ mature oligodendrocytes, and myelin thickness by the end of the first postnatal week. Co‐ordinate elevations in the pro‐myelinating signaling pathways ERK and AKT, expression of fatty acid 2‐hydroxylase, and myelin regulatory transcription factor were also observed in the spinal cord of 7d Klk6 knockouts. LC/MS/MS quantification of spinal cord lipids showed sphingosine and sphingomyelins to be elevated in Klk6 knockouts at the peak of myelination. Oligodendrocyte progenitor cells (OPCs)‐derived from Klk6 knockouts, or wild type OPCs‐treated with a Klk6 inhibitor (DFKZ‐251), also showed increased MBP and PLP. Moreover, inhibition of Klk6 in OPC cultures enhanced brain derived neurotrophic factor‐driven differentiation. Altogether, these findings suggest that oligodendrocyte‐derived Klk6 may operate as an autocrine or paracrine rheostat, or brake, on pro‐myelinating signaling serving to regulate myelin homeostasis developmentally and in the adult. These findings document for the first time that inhibition of Klk6 globally, or specifically in oligodendrocyte progenitors, is a strategy to increase early stages of oligodendrocyte differentiation and myelin production in the CNS.

AbstractExcessive activation of the thrombin receptor, protease activated receptor 1 (PAR1) is implicated in diverse neuropathologies from neurodegenerative conditions to neurotrauma. PAR1 knockout mice show improved outcomes after experimental spinal cord injury (SCI), however information regarding the underpinning cellular and molecular mechanisms is lacking. Here we demonstrate that genetic blockade of PAR1 in female mice results in improvements in sensorimotor co‐ordination after thoracic spinal cord lateral compression injury. We document improved neuron preservation with increases in Synapsin‐1 presynaptic proteins and GAP43, a growth cone marker, after a 30 days recovery period. These improvements were coupled to signs of enhanced myelin resiliency and repair, including increases in the number of mature oligodendrocytes, their progenitors and the abundance of myelin basic protein. These significant increases in substrates for neural recovery were accompanied by reduced astrocyte (Serp1) and microglial/monocyte (CD68 and iNOS) pro‐inflammatory markers, with coordinate increases in astrocyte (S100A10 and Emp1) and microglial (Arg1) markers reflective of pro‐repair activities. Complementary astrocyte‐neuron co‐culture bioassays suggest astrocytes with PAR1 loss‐of‐function promote both neuron survival and neurite outgrowth. Additionally, the pro‐neurite outgrowth effects of switching off astrocyte PAR1 were blocked by inhibiting TrkB, the high affinity receptor for brain derived neurotrophic factor. Altogether, these studies demonstrate unique modulatory roles for PAR1 in regulating glial‐neuron interactions, including the capacity for neurotrophic factor signaling, and underscore its position at neurobiological intersections critical for the response of the CNS to injury and the capacity for regenerative repair and restoration of function.