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.

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.

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.

Summary Background Orthodontic implant migration has been clinically observed in presence of continuous loading forces. Recent studies indicate that osteocytes play a crucial role in this phenomenon. Objectives Aim of this study was to investigate local osteocytic gene expression, protein expression, and bone micro-structure in peri-implant regions of pressure and tension. Material and methods The present work reports a complementary analysis to a previous micro-computed tomography study. Two customized mini-implants were placed in one caudal rat vertebra and connected by a nickel–titanium contraction spring generating different forces (i.e. 0, 0.5, 1.0, and 1.5 N). Either at 2 or 8 weeks, the vertebrae were harvested and utilized for 1. osteocytic gene expression using laser capture micro-dissection on frozen sections coupled with qPCR, 2. haematoxylin–eosin staining for qualitative and quantitative analyses, 3. immunofluorescence staining and analysis, and 4. bone-to-implant contact on undecalcified samples. Results At the two time points for all the performed analyses no significant differences were observed with respect to the applied force magnitudes and cell harvesting localization. However, descriptive histological analysis revealed remarkable bone remodelling at 2 weeks of loading. At 8 weeks the implants were osseointegrated and, especially in 1.0 and 1.5 N groups, newly formed bone presented a characteristic load bearing architecture with trabecula oriented in the direction of the loading. Conclusions The present study confirmed that stress-induced bone remodelling is the biological mechanism of orthodontic implant migration. Bone apposition was found at ‘tension’ and ‘pressure’ sites thus limiting implant migration over time.