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An update on the rod microglia variant in experimental and clinical brain injury and disease
Katherine R Giordano1,2, Charlotte R Denman2,3, Phoebe S Dubisch4
1BARROW Neurological Institute at Phoenix Children's Hospital, Phoenix, AZ, USA.
Abstract:
Contemporary microglia morphologies include ramified, activated and amoeboid, with the morphology of microglia considered highly coupled to the cellular function. Rod microglia are an additional activated microglia variant observed in the ageing, injured and diseased brain. Rod microglia were reported frequently in the early 1900s by neuropathologists in post-mortem cases of general paresis, Alzheimer's disease and encephalitis, and then remained largely ignored for almost 100 years. Recent reports have renewed interest in rod microglia, most notably after experimental traumatic brain injury. Rod microglia are formed by the narrowing of the soma and retraction of planar processes, which results in the appearance of an elongated, rod-shaped cell. Rod microglia are most commonly observed in the cortex, aligned perpendicular to the dural surface and adjacent to neuronal processes; in the hippocampus, they are aligned perpendicular to hippocampal layers. Furthermore, rod microglia form trains with one another, apical end to basal end. By replicating the process of sketching microscopic observation, rod microglia are re-defined by circumnutation around the long axis. In this update, we summarize the rod microglia variant in clinical and experimental literature and advocate for investigation into mechanisms of rod microglia origin and function.
Insights
Rod microglia, a distinct activated brain immune cell variant, are re-emerging in research after being overlooked for a century. Their unique shape and alignment in aged, injured, or diseased brains warrant further study into their function.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglia, the brain's resident immune cells, exhibit diverse morphologies linked to function.
- Rod microglia, an activated variant, were historically documented but largely ignored for nearly 100 years.
- Recent studies, particularly after traumatic brain injury, have reignited interest in rod microglia.
Purpose of the Study:
- To review the existing literature on rod microglia in clinical and experimental contexts.
- To re-define rod microglia morphology based on historical observations and modern understanding.
- To advocate for research into the mechanisms underlying rod microglia formation and function.
Main Methods:
- Review of historical neuropathology reports and contemporary scientific literature.
- Analysis of morphological characteristics, including soma narrowing and process retraction.
- Observation of cellular alignment and arrangement in brain tissue (cortex and hippocampus).
Main Results:
- Rod microglia are characterized by an elongated, rod-shaped cell body with retracted processes.
- They are typically found aligned perpendicular to brain surfaces or layers in aged, injured, and diseased brains.
- Rod microglia can form linear chains, end-to-end.
Conclusions:
- Rod microglia represent a significant, yet understudied, activated microglial state.
- Understanding their origin and function is crucial for comprehending brain aging, injury, and disease.
- Further investigation is needed to elucidate the specific roles of rod microglia in neuropathology.
