Emerging roles of astrocytes as immune effectors in the central nervous system.

The astrocyte, a major glial cell type in the central nervous system (CNS), is widely regarded as a functionally diverse mediator of homeostasis. During development and throughout adulthood, astrocytes have essential roles, such as providing neuron metabolic support, modulating synaptic function, and maintaining the blood-brain barrier (BBB). Recent evidence continues to underscore their functional heterogeneity and importance for CNS maintenance, as well as how these cells ensure optimal CNS and immune responses to disease, acute trauma, and infection. Advances in our understanding of neuroimmune interactions complement our knowledge of astrocyte functional heterogeneity, where astrocytes are now regarded as key effectors and propagators of immune signaling. This shift in perspective highlights the role of astrocytes not merely as support cells, but as active participants in CNS immune responses.

Characteristics of blood-brain barrier heterogeneity between brain regions revealed by profiling vascular and perivascular cells.

The blood-brain barrier (BBB) protects the brain and maintains neuronal homeostasis. BBB properties can vary between brain regions to support regional functions, yet how BBB heterogeneity occurs is poorly understood. Here, we used single-cell and spatial transcriptomics to compare the mouse median eminence, one of the circumventricular organs that has naturally leaky blood vessels, with the cortex. We identified hundreds of molecular differences in endothelial cells (ECs) and perivascular cells, including astrocytes, pericytes and fibroblasts. Using electron microscopy and an aqueous-based tissue-clearing method, we revealed distinct anatomical specializations and interaction patterns of ECs and perivascular cells in these regions. Finally, we identified candidate regionally enriched EC-perivascular cell ligand-receptor pairs. Our results indicate that both molecular specializations in ECs and unique EC-perivascular cell interactions contribute to BBB functional heterogeneity. This platform can be used to investigate BBB heterogeneity in other regions and may facilitate the development of central nervous system region-specific therapeutics.

Longitudinal scRNA-seq analysis in mouse and human informs optimization of rapid mouse astrocyte differentiation protocols.

Macroglia (astrocytes and oligodendrocytes) are required for normal development and function of the central nervous system, yet many questions remain about their emergence during the development of the brain and spinal cord. Here we used single-cell/single-nucleus RNA sequencing (scRNA-seq/snRNA-seq) to analyze over 298,000 cells and nuclei during macroglia differentiation from mouse embryonic and human-induced pluripotent stem cells. We computationally identify candidate genes involved in the fate specification of glia in both species and report heterogeneous expression of astrocyte surface markers across differentiating cells. We then used our transcriptomic data to optimize a previous mouse astrocyte differentiation protocol, decreasing the overall protocol length and complexity. Finally, we used multi-omic, dual single-nuclei (sn)RNA-seq/snATAC-seq analysis to uncover potential genomic regulatory sites mediating glial differentiation. These datasets will enable future optimization of glial differentiation protocols and provide insight into human glial differentiation.

Biomechanical evaluation of parasagittal occipital plating: screw load sharing analysis.

STUDY DESIGN: Biomechanical evaluation of occipitocervical instrumentation techniques. OBJECTIVE: Compare methods of occipital instrumentation by quantifying load sharing of occipital screws and measuring motion across instrumented occipitocervical spines. SUMMARY OF BACKGROUND DATA: Newer occipitocervical plate/screw systems that attach to longitudinal rods have been developed to improve fixation. These devices place screws in the center of occipital bone or off-midline. Midline plates offer screw purchase in thicker bone. Off-midline systems may increase the effective moment arm for torsional and lateral bending control. Measurement of screw loads within occipital plates is useful for determining optimal plate configuration. METHODS: Ten cadaveric specimens (occiput-C4) were tested in flexion/extension (FE), lateral bending (LAT), and axial rotation (ROT) over +/-3 Nm pure moment. After intact testing, 4 occipitocervical fixation constructs were tested using washer load cells to assess loading across screws used to fix the plates to the occiput. Parasagittal occipital plates were positioned either convex or concave side facing medially. Each plate was first fixed using 3 screws (rostral, middle, caudal), then with the caudal screw eliminated (simulated failure). Range of motion (ROM) and peak screw loads are reported. RESULTS: ROM decreased from intact to any of the 4 fusion plate configurations in FE, LAT, and ROT (P << 0.05), but not between plate configurations. Screw load significantly decreased from medially convex to medially concave configurations in LAT, but no significant changes were observed in FE or ROT. With caudal screws removed, middle screws peak loads significantly increased in FE and LAT (P < 0.05), but not ROT. CONCLUSION: Occipital screw placement off-midline improves screw loads under lateral bending forces on occipitocervical constructs, though loads for FE and ROT are unchanged. As screws pullout, the loads may be redistributed, resulting in increased screw pullout forces above. Despite the improvement in screw loads for laterally based plates during lateral bending, overall ROM across the occipitocervical junction is unchanged.