Major Histocompatibility Complex class I proteins are critical for maintaining neuronal structural complexity in the...

Area of Science:

• Neuroscience
• Immunology
• Aging Research

Background:

• Major histocompatibility complex class I (MHCI) proteins are known to influence neuronal development, including synapse formation and memory.
• The role of MHCI in the aging brain, particularly concerning non-pathological aging processes, remains largely unexplored.

Purpose of the Study:

• To investigate the impact of MHCI deficiency on neuronal structure and synaptic integrity in the aged hippocampus.
• To determine if MHCI plays a role in maintaining brain health during aging.

Main Methods:

• Utilized aged (12-month-old) MHCI knockout mice and wild-type littermates.
• Performed detailed ultrastructural analyses of hippocampal neurons, focusing on dendritic morphology and spine characteristics.
• Quantified synapse density and analyzed the morphology of individual synapses, including spine head diameter and postsynaptic density (PSD) area.
• Assessed the expression levels of key synaptic proteins, including glutamate receptors (GluN2B, GluA2/3), VGluT1, PSD95, and synaptophysin.

Main Results:

• MHCI deficiency led to significant dendritic atrophy and altered spine populations (increased thin spines, decreased stubby spines) in aged mice.
• Ultrastructural analysis revealed smaller spine head diameters, reduced PSD areas, increased overall synapse density, and a higher proportion of small, non-perforated spines.
• These synaptic changes were observed to emerge relatively late, after 6 months of age.
• Aged MHCI knockout mice showed an age-dependent increase in GluN2B levels, without significant changes in other assessed synaptic proteins.

Conclusions:

• MHCI plays a crucial role in maintaining neuronal and synaptic integrity in the aged brain, beyond its developmental functions.
• MHCI deficiency contributes to age-related changes in dendritic morphology and synaptic structure, potentially impacting cognitive function.
• The observed alterations in synaptic proteins like GluN2B suggest a mechanism through which MHCI influences synaptic function during aging.