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Updated: Jun 2, 2026
Assessing the Expression of Major Histocompatibility Complex Class I on Primary Murine Hippocampal Neurons by Flow Cytometry
Published on: May 19, 2020
A potential role for shed soluble major histocompatibility class I molecules as modulators of neurite outgrowth
Lorraine R Washburn1, Dan Zekzer, Shoshana Eitan
1Department of Molecular and Medical Pharmacology, University of California Los Angeles, Los Angeles, California, United States of America.
Insights
Major histocompatibility class I (MHCI) molecules, when soluble, inhibit neuronal connection formation. This soluble MHCI
Area of Science:
- Neurobiology
- Immunology
- Molecular Biology
Background:
- The neurobiological functions of major histocompatibility class I (MHCI) molecules are not well understood.
- MHCI molecules are known to be involved in immune responses and can be released in soluble forms (sMHCI).
Purpose of the Study:
- To investigate the role of MHCI in the formation of neuronal connections.
- To determine if soluble MHCI (sMHCI) affects neurite outgrowth.
Main Methods:
- Cultured embryonic mouse retina and thalamic explants.
- Utilized wildtype and transgenic mice (NSE-Db) with altered MHCI expression.
- Analyzed neurite outgrowth in proximity to explants.
- Investigated the effect of sMHCI from engineered cells on neuronal cultures.
- Tested the impact of cAMP levels on sMHCI's neuroinhibitory effect.
Main Results:
- Retina neurite outgrowth was significantly inhibited near thalami overexpressing MHCI.
- The inhibitory factor released from these thalami was identified as sMHCI.
- Engineered cells expressing MHCI released sMHCI that inhibited neurite outgrowth in vitro.
- The neuroinhibitory effect of sMHCI was blocked by reducing cAMP levels.
Conclusions:
- Soluble MHCI (sMHCI) acts as a neuroinhibitor, affecting neurite outgrowth.
- Neuronal signaling pathways involving cyclic nucleotides may mediate MHCI's effects.
- MHCI influences neural development not only in its membrane-bound form but also as a soluble molecule.
Abstract:
The neurobiological activities of classical major histocompatibility class I (MHCI) molecules are just beginning to be explored. To further examine MHCI's actions during the formation of neuronal connections, we cultured embryonic mouse retina explants a short distance from wildtype thalamic explants, or thalami from transgenic mice (termed "NSE-Db") whose neurons express higher levels of MHCI. While retina neurites extended to form connections with wildtype thalami, we were surprised to find that retina neurite outgrowth was very stunted in regions proximal to NSE-Db thalamic explants, suggesting that a diffusible factor from these thalami inhibited retina neurite outgrowth. It has been long known that MHCI-expressing cells release soluble forms of MHCI (sMHCI) due to the shedding of intact MHCI molecules, as well as the alternative exon splicing of its heavy chain or the action proteases which cleave off it's transmembrane anchor. We show that the diffusible inhibitory factor from the NSE-Db thalami is sMHCI. We also show that COS cells programmed to express murine MHCI release sMHCI that inhibits neurite outgrowth from nearby neurons in vitro. The neuroinhibitory effect of sMHCI could be blocked by lowering cAMP levels, suggesting that the neuronal MHCI receptor's signaling mechanism involves a cyclic nucleotide-dependent pathway. Our results suggest that MHCI may not only have neurobiological activity in its membrane-bound form, it may also influence local neurons as a soluble molecule. We discuss the involvement of complement proteins in generating sMHCI and new theoretical models of MHCI's biological activities in the nervous system.
