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Published on: March 25, 2016
Pial Vessel-Associated Microglia/Macrophages Increase in Female Dahl-SS/Jr Rats Independent of Pregnancy History
Junie P Warrington1,2, Qingmei Shao1, Ahsia M Clayton1
1Department of Neurology, University of Mississippi Medical Center, Jackson, MS 39216, USA.
Abstract:
As the resident immune cells of the central nervous system, microglia have a wide range of functions such as surveillance, phagocytosis, and signaling through production of chemokines and cytokines. Recent studies have identified and characterized macrophages residing at the meninges, a series of layers surrounding the brain and spinal cord. While perivascular microglia within the brain parenchyma increase following chronic hypertension, there are no reports of changes at the meninges, and specifically, associated with the pial vasculature. Thus, we used female Sprague Dawley and Dahl salt-sensitive (SS/Jr) rat brains, stained for ionized calcium-binding adapter molecule (Iba1), and characterized microglia/macrophages associated with pial vessels in the posterior brain. Results indicate that Iba1+ pial vessel-associated microglia (PVAM) completely surrounded the vessels in brains from the Dahl-SS/Jr rats. PVAM density was significantly higher and distance between PVAMs lower in Dahl-SS/Jr compared to the Sprague Dawley rat brains. Pregnancy history did not affect these findings. While the functional role of these cells are not known, we contextualize our novel findings with that of other studies assessing or characterizing myeloid cells at the borders of the CNS (meninges and choroid plexus) and perivascular macrophages and propose their possible origin in the Dahl-SS/Jr model of chronic hypertension.
Insights
Chronic hypertension alters brain immune cells. In Dahl-SS/Jr rats, pial vessel-associated microglia (PVAM) significantly increased around cerebral blood vessels, suggesting a role in hypertension-related brain changes.
Area of Science:
- Neuroimmunology
- Central Nervous System (CNS) Immunity
- Vascular Biology
Background:
- Microglia are key immune cells within the CNS, performing surveillance and signaling functions.
- Macrophages have been identified in the meninges, the protective layers surrounding the brain and spinal cord.
- While perivascular microglia increase in the brain parenchyma during chronic hypertension, changes in meningeal immune cells, particularly near pial vessels, remain uncharacterized.
Purpose of the Study:
- To investigate changes in microglia/macrophages associated with pial vasculature in the context of chronic hypertension.
- To compare these immune cells in a hypertensive rat model (Dahl salt-sensitive, SS/Jr) versus a normotensive control (Sprague Dawley).
Main Methods:
- Utilized female Sprague Dawley and Dahl-SS/Jr rat brains.
- Performed immunohistochemical staining for ionized calcium-binding adapter molecule 1 (Iba1) to identify microglia/macrophages.
- Characterized and quantified Iba1-positive pial vessel-associated microglia (PVAM) in the posterior brain region.
Main Results:
- Iba1-positive PVAM were observed to completely surround pial vessels in Dahl-SS/Jr rat brains.
- Dahl-SS/Jr rats exhibited significantly higher PVAM density and lower inter-PVAM distance compared to Sprague Dawley rats.
- Pregnancy history did not influence the observed PVAM findings.
Conclusions:
- Chronic hypertension is associated with a significant increase in PVAM density around cerebral blood vessels in the Dahl-SS/Jr rat model.
- These findings highlight a novel alteration of myeloid cell populations at the brain's meningeal border in hypertension.
- The study contextualizes these results with existing literature on CNS border myeloid cells and proposes potential origins for PVAM in this hypertensive model.
