Rose, J. J. | Search bioRxiv

bioRxiv2024

Distinct functional classes of CA1 hippocampal interneurons are modulated by cerebellar stimulation in a coordinated manner

There is mounting evidence that the cerebellum impacts hippocampal functioning, but the impact of the cerebellum on hippocampal interneurons remains obscure. Using miniscopes in freely behaving animals, we find optogenetic stimulation of Purkinje cells alters the calcium activity of a large percentage of CA1 interneurons. This includes both increases and decreases in activity. Remarkably, this bidirectional impact occurs in a coordinated fashion, in line with interneurons functional properties. Specifically, CA1 interneurons activated by cerebellar stimulation are commonly locomotion-active, while those inhibited by cerebellar stimulation are commonly rest-active interneurons. We additionally find that subsets of CA1 interneurons show altered activity during object investigations, suggesting a role in the processing of objects in space. Importantly, these neurons also show coordinated modulation by cerebellar stimulation: CA1 interneurons that are activated by cerebellar stimulation are more likely to be activated, rather than inhibited, during object investigations, while interneurons that show decreased activity during cerebellar stimulation show the opposite profile. Therefore, CA1 interneurons play a role in object processing and in cerebellar impacts on the hippocampus, providing insight into previously noted altered CA1 processing of objects in space with cerebellar stimulation. We examined two different stimulation locations (IV/V Vermis; Simplex) and two different stimulation approaches (7Hz or a single 1s light pulse) - in all cases, the cerebellum induces similar coordinated CA1 interneuron changes congruent with an explorative state. Overall, our data show that the cerebellum impacts CA1 interneurons in a bidirectional and coordinated fashion, positioning them to play an important role in cerebello-hippocampal communication. Significance StatementAcute manipulation of the cerebellum can affect the activity of cells in CA1, and perturbing normal cerebellar functioning can affect hippocampal-dependent spatial processing, including the processing of objects in space. Despite the importance of interneurons on the local hippocampal circuit, it was unknown how cerebellar activation impacts CA1 inhibitory neurons. We find that stimulating the cerebellum robustly affects multiple populations of CA1 interneurons in a bidirectional, coordinated manner, according to their functional profiles during behavior, including locomotion and object investigations. Our work also provides support for a role of CA1 interneurons in spatial processing of objects, with populations of interneurons showing altered activity during object investigations.

neuroscience↗

bioRxiv2022

Single-cell Landscape Analysis of the Circulating Human B Cell Pool under Selective Pressure of Allogeneic Stem Cell Transplantation

Alloreactivity can drive autoimmune syndromes. After allogeneic hematopoietic stem cell transplantation (allo-HCT) chronic graft-versus-host disease (cGVHD), a B cell-mediated autoimmune-like syndrome, commonly occurs. Because donor-derived B cells continually develop under selective pressure from host alloantigens, aberrant B Cell Receptor (BCR)-activation and IgG production can emerge and contribute to cGVHD pathobiology. To better understand molecular programing of B cells under selective pressure of alloantigens, we performed scRNA-Seq analysis on high numbers of purified B cells from allo-HCT patients. An unsupervised analysis revealed 10 clusters, distinguishable by signature genes for maturation, activation and memory. We found striking transcriptional differences in the memory B cell compartment after allo-HCT compared to healthy or infected individuals. To identify intrinsic properties when B-cell tolerance is lost after allo-HCT, we then assessed clusters for differentially expressed genes (DEGs) between patients with vs. without autoimmune-like manifestations (Active cGVHD vs. No cGVHD, respectively). DEGs were found in Active cGVHD in both naive and BCR-activated clusters, suggesting functional diversity. Some DEGs were also differentially expressed across most clusters, suggesting common molecular programs that may promote B cell plasticity. Our study of human allo-HCT and cGVHD provides new understanding of B-cell memory in the face of chronic alloantigen stimulation. One Sentence SummaryOur scRNA-Seq study of purified B cells after allo-HCT clarifies molecular differences in human B cell subsets when immune tolerance is lost or maintained. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=80 SRC="FIGDIR/small/512162v4_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@5c452eorg.highwire.dtl.DTLVardef@1c1d34borg.highwire.dtl.DTLVardef@171310org.highwire.dtl.DTLVardef@e4bf15_HPS_FORMAT_FIGEXP M_FIG C_FIG The circulating human B cell compartment under the selective pressure of allogeneic hematopoietic stem cell transplantation (Allo-HCT) has an intrinsically altered memory B cell pool. In allo-HCT, genetically disparate donor stem and progenitor cells engraft, regenerating a new peripheral B cell compartment in the host. During ongoing B lymphopoiesis and diversification, selective pressure from alloantigens and other extrinsic factors, including B Cell Activating Factor (BAFF), result in either B cell maturation and immune tolerance (No Chronic GVHD) or altered B cell homeostasis and autoimmune manifestations (Active Chronic GVHD). B cells within defined subsets in patients with Active GVHD have distinct intrinsic programs delineated by differentially expressed genes (DEGs). Some DEGs occur across nearly all B cell subsets ( Differentially Expressed Broadly), while other DEGs are more restricted within only one or a few B cell subsets ( Naive, BCR-activated, or Memory). We affirm altered trajectories for diversification (blue arrow) and enrichment of an atypical memory B cell (ABC) pool, with intrinsic differences when chronic GVHD occurs.

immunology↗