Diverse Subtypes of Olfactory Ensheathing Cells Exhibit Distinct Gene Expression Profiles and Regenerative Functions

Core Concepts

Olfactory ensheathing cells (OECs) are a unique hybrid glial cell type that exhibit diverse subtypes with distinct gene expression patterns and functions related to neural repair and regeneration.

Abstract

This study used single-cell RNA sequencing (scRNA-seq) to characterize the gene expression profiles of immunopurified olfactory ensheathing cells (OECs) derived from the adult rat olfactory bulb. The analysis revealed five distinct OEC subtypes, each expressing unique marker genes and pathways indicative of progenitor, axonal regeneration, secreted molecule, and microglia-like functions. The key findings are: Purified OECs express higher levels of stress response and proliferation genes compared to unpurified OEC cultures containing fibroblasts and microglia. The five OEC subtypes identified include: Cluster 0: Enriched in genes related to extracellular matrix organization and myelination Cluster 1: Expresses classic OEC markers and genes involved in nervous system development and axon regeneration Cluster 2: Characterized by cell cycle and proliferation genes, representing a progenitor-like OEC subtype Cluster 3: Expresses both OEC and microglia/macrophage markers, suggesting an immune-modulatory function Cluster 4: Shows characteristics of astrocytes and oligodendrocytes Trajectory and ligand-receptor network analyses indicate potential plasticity and communication between the OEC subtypes. Spatial validation in the olfactory bulb confirmed the presence and distribution of the defined OEC subtypes. OECs were found to synthesize and secrete the extracellular matrix proteins Reelin and Connective Tissue Growth Factor (CTGF), which are important for neural repair and axon outgrowth. These findings provide a comprehensive understanding of the heterogeneity and regenerative properties of OECs, which have significant implications for their use in neural repair strategies.

Stats

Olfactory ensheathing cells (OECs) express higher levels of stress response genes (Cryab, Nqo1, Postn) compared to OECs in leftover cultures. OECs in cluster 2 express high levels of cell cycle and proliferation genes (Mki67, Stmn1, Cdk1). OECs in cluster 3 express genes involved in lysosome function (Cst3, Ctsz, Laptm5) and the complement system (C1qa, C1qb, C1qc). OECs synthesize and secrete the extracellular matrix proteins Reelin and Connective Tissue Growth Factor (CTGF).

Quotes

"OECs represent a hybrid glial cell that promote neural repair." "Our results further support the activities of OECs in modulating immune responses, based on the expression of genes involved in the endocytosis of bacteria, the regulation of microglia activation, and the expression of numerous lysosomal pathways." "OECs secrete both Reelin and Connective tissue growth factor, extracellular matrix molecules which are important for neural repair and axonal outgrowth."

Key Insights Distilled From

Olfactory ensheathing cells are hybrid glial cells that promote neural repair

by Phelps,P. E.... at www.biorxiv.org 12-21-2023

https://www.biorxiv.org/content/10.1101/2023.12.20.572462v1

Deeper Inquiries

What are the functional differences between the five OEC subtypes identified in this study, and how might they contribute to neural repair in different ways

The five subtypes of OECs identified in this study exhibit distinct functional differences that could contribute to neural repair in various ways. Cluster 0 - Matricellular Proteins: This subtype is rich in genes related to extracellular matrix organization and collagen biosynthesis. The expression of matricellular proteins like Ccn2/Ctgf and Ccn3/NOV suggests a role in wound healing and injury repair. These OECs may facilitate axon regeneration by modulating the extracellular environment to support growth. Cluster 1 - Classic OEC Markers: This subtype expresses classic OEC markers and genes associated with nervous system development and axon regeneration. The presence of growth factors like Bdnf and Btc indicates a potential role in promoting neuronal survival and neurite outgrowth. Cluster 2 - Proliferative OECs: These OECs are characterized by cell cycle and proliferative markers. They may contribute to neural repair by actively proliferating and generating new cells to support regeneration and repair processes. Cluster 3 - Microglia-like OECs: This subtype shows expression of microglia markers and genes involved in immune responses. These OECs may play a role in modulating the immune environment at the injury site and clearing debris to create a conducive environment for repair. Cluster 4 - Astrocyte and Oligodendrocyte Characteristics: OECs in this subtype express genes associated with astrocytes and oligodendrocytes. They may contribute to neural repair by regulating synaptic connectivity and ECM organization, potentially influencing axon growth and repair. The functional diversity of these OEC subtypes suggests that they may work synergistically to promote neural repair through a combination of extracellular matrix modulation, growth factor secretion, immune response modulation, and cell proliferation.

How do the gene expression profiles and secreted factors of OECs compare to other glial cell types, and what insights does this provide into the unique regenerative properties of OECs

The gene expression profiles and secreted factors of OECs compared to other glial cell types provide insights into the unique regenerative properties of OECs. Overlap with Schwann Cells: OECs share substantial gene expression similarities with Schwann cells, including markers for myelination and growth factor production. This overlap suggests that OECs may possess similar regenerative capabilities to Schwann cells, supporting axon growth and repair. Similarities with Astrocytes and Oligodendrocytes: OECs also express genes associated with astrocytes and oligodendrocytes, indicating potential roles in synaptic connectivity, ECM organization, and myelination. These similarities suggest that OECs may have multifaceted functions related to neural repair beyond axon regeneration. Microglia-like Functions: The expression of microglia markers and genes involved in immune responses in OECs highlights their role in modulating the immune environment at injury sites. This immune modulation may contribute to creating a favorable environment for neural repair and regeneration. Unique Secreted Factors: OECs secrete molecules like Reelin and Ctgf, which are important for neural repair and axonal outgrowth. These factors may play a crucial role in promoting axon regeneration and creating a supportive environment for neural repair processes. The diverse gene expression profiles and secreted factors of OECs suggest that they possess a unique combination of regenerative properties that set them apart from other glial cell types, making them valuable candidates for neural repair therapies.

Given the heterogeneity of OECs, how might future therapeutic strategies utilizing OECs for neural repair need to be tailored to target specific OEC subtypes or combinations of subtypes

Given the heterogeneity of OECs, future therapeutic strategies utilizing OECs for neural repair may need to be tailored to target specific OEC subtypes or combinations of subtypes to maximize their regenerative potential. Targeted Subtype Therapies: Understanding the distinct functions of each OEC subtype can help in developing targeted therapies. For example, therapies focusing on promoting axon regeneration may benefit from utilizing OECs from Cluster 0, rich in matricellular proteins. Combination Approaches: Combining different OEC subtypes with complementary functions could enhance the overall regenerative capacity. For instance, a combination of proliferative OECs from Cluster 2 and immune-modulating OECs from Cluster 3 may provide a comprehensive approach to neural repair. Personalized Treatment: Tailoring OEC therapies based on the specific needs of individual patients and the nature of their neural injuries could optimize treatment outcomes. By selecting the most appropriate OEC subtypes for each case, personalized regenerative strategies can be developed. Overall, leveraging the heterogeneity of OEC subtypes and understanding their unique contributions to neural repair can lead to more effective and targeted therapeutic interventions for various neurological conditions.