Hippocampal neurogenesis undergoes dramatic age‐related changes. Mice with targeted deletion of the clock gene Bmal1 (Bmal1‐/‐) show disrupted regulation of reactive oxygen species homeostasis, accelerated aging, neurodegeneration and cognitive deficits. As proliferation of neuronal progenitor/precursor cells (NPCs) is enhanced in young Bmal1‐/‐ mice, we tested the hypothesis that this results in premature aging of hippocampal neurogenic niche in adult Bmal1‐/‐ mice as compared to wildtype littermates. We found significantly reduced pool of hippocampal NPCs, scattered distribution, enhanced survival of NPCs and an increased differentiation of NPCs into the astroglial lineage at the expense of the neuronal lineage. Immunoreaction of the redox sensitive histone deacetylase Sirtuine 1, peroxisomal membrane protein at 70kDa and expression of the cell cycle inhibitor p21 Waf1/CIP1 were increased in adult Bmal1‐/‐ mice. In conclusion, genetic disruption of the molecular clockwork leads to accelerated age‐dependent decline in adult neurogenesis presumably as a consequence of oxidative stress.

Purinergic P2X and P2Y receptors are involved in mediating intercellular signalling via purines such as adenosine triphosphate (ATP). P2X and P2Y receptors have been implicated in numerous body functions including learning, memory and sleep. All of these body functions show time-of–day-dependent variations controlled by the master circadian oscillator located in the suprachiasmatic nucleus (SCN). Evidence exists for a role of purinergic signalling in intercellular coupling within SCN. However, few studies have been performed on the expression of purinergic receptors in SCN. Therefore, we analyse the expression of seven P2X (P2X1–7) and eight P2Y (P2Y1–2, 4, 6, 11–14) receptors in mouse SCN and address their time-of-day-dependent variation by using immunohistochemistry and real-time polymerase chain reaction. At the early light phase, P2X and P2Y receptors show a low to moderate, homogenously distributed immunoreaction throughout SCN. P2Y13 reveals strong immunoreaction in fibres within the core region of SCN. From the fifteen analysed P2 receptors, seven exhibit a time-of-day-dependent variation in SCN. P2X1 immunoreaction is very low in the early light phase with a minor increase at the end of the dark phase. P2X4 immunoreaction strongly increases during the dark phase in soma cells in the core region and in a dense network of fibres in the shell region of SCN. P2X3 immunoreaction is moderately elevated during the dark phase. Conversely, immunoreaction for P2Y2, P2Y12 and P2Y14 moderately increases at the early light phase and P2Y6 immunoreaction displays a moderate increase at the mid-light phase. Thus, this study demonstrates a time-of-day-dependent variation of P2 receptors in mouse SCN.Electronic supplementary materialThe online version of this article (doi:10.1007/s00441-017-2634-8) contains supplementary material, which is available to authorized users.

Bmal1 is an essential component of the molecular clockwork, which drives circadian rhythms in cell function. In Bmal1‐deficient (Bmal1−/−) mice, chronodisruption is associated with cognitive deficits and progressive brain pathology including astrocytosis indicated by increased expression of glial fibrillary acidic protein (GFAP). However, relatively little is known about the impact of Bmal1‐deficiency on astrocyte morphology prior to astrocytosis. Therefore, in this study we analysed astrocyte morphology in young (6–8 weeks old) adult Bmal1−/− mice. At this age, overall GFAP immunoreactivity was not increased in Bmal1‐deficient mice. At the ultrastructural level, we found a decrease in the volume fraction of the fine astrocytic processes that cover the hippocampal mossy fiber synapse, suggesting an impairment of perisynaptic processes and their contribution to neurotransmission. For further analyses of actin cytoskeleton, which is essential for distal process formation, we used cultured Bmal1−/− astrocytes. Bmal1−/− astrocytes showed an impaired formation of actin stress fibers. Moreover, Bmal1−/− astrocytes showed reduced levels of the actin‐binding protein cortactin (CTTN). Cttn promoter region contains an E‐Box like element and chromatin immunoprecipitation revealed that Cttn is a potential Bmal1 target gene. In addition, the level of GTP‐bound (active) Rho‐GTPase (Rho‐GTP) was reduced in Bmal1−/− astrocytes. In summary, our data demonstrate that Bmal1‐deficiency affects morphology of the fine astrocyte processes prior to strong upregulation of GFAP, presumably because of impaired Cttn expression and reduced Rho‐GTP activation. These morphological changes might result in altered synaptic function and, thereby, relate to cognitive deficits in chronodisruption.

Background The astroglial connexins Cx30 and Cx43 contribute to many important CNS functions including cognitive behaviour, motoric capacity and regulation of the sleep-wake cycle. The sleep wake cycle, is controlled by the circadian system. The central circadian rhythm generator resides in the suprachiasmatic nucleus (SCN). SCN neurons are tightly coupled in order to generate a coherent circadian rhythm. The SCN receives excitatory glutamatergic input from the retina which mediates entrainment of the circadian system to the environmental light-dark cycle. Connexins play an important role in electric coupling of SCN neurons and astrocytic-neuronal signalling that regulates rhythmic SCN neuronal activity. However, little is known about the regulation of Cx30 and Cx43 expression in the SCN, and the role of these connexins in light entrainment of the circadian system and in circadian rhythm generation. Methods We analysed time-of-day dependent as well as circadian expression of Cx30 and Cx43 mRNA and protein in the mouse SCN by means of qPCR and immunohistochemistry. Moreover, we analysed rhythmic spontaneous locomotor activity in mice with a targeted deletion of Cx30 and astrocyte specific deletion of Cx43 (DKO) in different light regimes by means of on-cage infrared detectors. Results Fluctuation of Cx30 protein expression is strongly dependent on the light-dark cycle whereas fluctuation of Cx43 protein expression persisted in constant darkness. DKO mice entrained to the light-dark cycle. However, re-entrainment after a phase delay was slightly impaired in DKO mice. Surprisingly, DKO mice were more resilient to chronodisruption. Conclusion Circadian fluctuation of Cx30 and Cx43 protein expression in the SCN is differently regulated. Cx30 and astroglial Cx43 play a role in rhythm stability and re-entrainment under challenging conditions. Electronic supplementary material The online version of this article (10.1186/s12964-019-0370-2) contains supplementary material, which is available to authorized users.

We demonstrate the impact of a disrupted molecular clock in Bmal1-deficient (Bmal1 −/− ) mice on migration of neural progenitor cells (NPCs). Proliferation of NPCs in rostral migratory stream (RMS) was reduced in Bmal1 −/− mice, consistent with our earlier studies on adult neurogenesis in hippocampus. However, a significantly higher number of NPCs from Bmal1 −/− mice reached the olfactory bulb as compared to wild-type littermates (Bmal1 +/+ mice), indicating a higher migration velocity in Bmal1 −/− mice. In isolated NPCs from Bmal1 −/− mice, not only migration velocity and expression pattern of genes involved in detoxification of reactive oxygen species were affected, but also RNA oxidation of catalase was increased and catalase protein levels were decreased. Bmal1 +/+ migration phenotype could be restored by treatment with catalase, while treatment of NPCs from Bmal1 +/+ mice with hydrogen peroxide mimicked Bmal1 −/− migration phenotype. Thus, we conclude that Bmal1 deficiency affects NPC migration as a consequence of dysregulated detoxification of reactive oxygen species. Electronic supplementary material The online version of this article (10.1007/s00429-018-1775-1) contains supplementary material, which is available to authorized users.