Multi-Domain Cognitive Assessment of Male Mice Shows Space Radiation Is Not Harmful to High-Level Cognition and Actually Improves Pattern Separation

Astronauts on interplanetary missions - such as to Mars - will be exposed to space radiation, a spectrum of highly-charged, fast-moving particles that includes 56Fe and 28Si. Earth-based preclinical studies show space radiation decreases rodent performance in low- and some high-level cognitive tasks. Given astronaut use of touchscreen platforms during training and space flight and given the ability of rodent touchscreen tasks to assess functional integrity of brain circuits and multiple cognitive domains in a non-aversive way, here we exposed 6-month-old C57BL/6J male mice to whole-body space radiation and subsequently assessed them on a touchscreen battery. Relative to Sham treatment, 56Fe irradiation did not overtly change performance on tasks of visual discrimination, reversal learning, rule-based, or object-spatial paired associates learning, suggesting preserved functional integrity of supporting brain circuits. Surprisingly, 56Fe irradiation improved performance on a dentate gyrus-reliant pattern separation task; irradiated mice learned faster and were more accurate than controls. Improved pattern separation performance did not appear to be touchscreen-, radiation particle-, or neurogenesis-dependent, as 56Fe and 28Si irradiation led to faster context discrimination in a non-touchscreen task and 56Fe decreased new dentate gyrus neurons relative to Sham. These data urge revisitation of the broadly-held view that space radiation is detrimental to cognition

Functional and mechanistic exploration of an adult neurogenesis-promoting small molecule

Adult neurogenesis occurs throughout life in the mammalian hippocampus and is essential for memory and mood control. There is significant interest in identifying ways to promote neurogenesis and ensure maintenance of these hippocampal functions. Previous work with a synthetic small molecule, isoxazole 9 (Isx-9), highlighted its neuronal-differentiating properties in vitro. However, the ability of Isx-9 to drive neurogenesis in vivo or improve hippocampal function was unknown. Here we show that Isx-9 promotes neurogenesis in vivo, enhancing the proliferation and differentiation of hippocampal subgranular zone (SGZ) neuroblasts, and the dendritic arborization of adult-generated dentate gyrus neurons. Isx-9 also improves hippocampal function, enhancing memory in the Morris water maze. Notably, Isx-9 enhances neurogenesis and memory without detectable increases in cellular or animal activity or vascularization. Molecular exploration of Isx-9-induced regulation of neurogenesis (via FACS and microarray of SGZ stem and progenitor cells) suggested the involvement of the myocyte-enhancer family of proteins (Mef2). Indeed, transgenic-mediated inducible knockout of all brain-enriched Mef2 isoforms (Mef2a/c/d) specifically from neural stem cells and their progeny confirmed Mef2's requirement for Isx-9-induced increase in hippocampal neurogenesis. Thus, Isx-9 enhances hippocampal neurogenesis and memory in vivo, and its effects are reliant on Mef2, revealing a novel cell-intrinsic molecular pathway regulating adult neurogenesis.—Petrik, D., Jiang, Y., Birnbaum, S. G., Powell, C. M., Kim, M.-S., Hsieh, J., Eisch, A. J. Functional and mechanistic exploration of an adult neurogenesis-promoting small molecule

Intravenous high-dose enzyme replacement therapy with recombinant palmitoyl-protein thioesterase reduces visceral lysosomal storage and modestly prolongs survival in a preclinical mouse model of infantile neuronal ceroid lipofuscinosis

PPT1-related neuronal ceroid lipofuscinosis (NCL) is a lysosomal storage disorder caused by deficiency in a soluble lysosomal enzyme, palmitoyl-protein thioesterase-1 (PPT1). Enzyme replacement therapy (ERT) has not been previously examined in a preclinical animal model. Homozygous PPT1 knockout mice reproduce the known features of the disease, developing signs of motor dysfunction at 5 months of age and death by around 8 months. In the current study, PPT1 knockout mice were treated with purified recombinant PPT1 (0.3 mg, corresponding to 12 mg/kg or 180 U/kg for a 25 g mouse) administered intravenously weekly either 1) from birth; or 2) beginning at 8 weeks of age. The treatment was surprisingly well tolerated and neither anaphylaxis nor antibody formation was observed. In mice treated from birth, survival increased from 236 to 271 days (p<0.001) and the onset of motor deterioration was similarly delayed. In mice treated beginning at 8 weeks, no increases in survival or motor performance were seen. An improvement in neuropathology in the thalamus was seen at 3 months in mice treated from birth, and although this improvement persisted it was attenuated by 7 months. Outside the central nervous system, substantial clearance of autofluorescent storage material in many tissues was observed. Macrophages in spleen, liver and intestine were especially markedly improved, as were acinar cells of the pancreas and tubular cells of the kidney. These findings suggest that ERT may be an option for addressing visceral storage as part of a comprehensive approach to PPT1-related NCL, but more effective delivery methods to target the brain are needed