Hippocampal angiogenesis and progenitor cell proliferation are increased with antidepressant use in major depression

Abstract

Background: Adult neurogenesis is coupled to angiogenesis in neurogenic niches in the dentate gyrus (DG) and increased by antidepressants in rodents. We hypothesized that, in major depressive disorder (MDD), antidepressants increase neural progenitor cells (NPCs) and capillaries in the human DG.

Methods: Neural progenitor cells and capillaries, detected on hippocampal sections by immunohistochemistry for neural stem cell protein, were quantified by stereology in matched MDDs (untreated, n = 12), MDD treated with selective serotonin reuptake inhibitors (MDD*SSRI, n = 6) or tricyclic antidepressants (MDD*TCA, n = 6), and nonpsychiatric control subjects (n = 12), all confirmed by psychological autopsy.

Results: The MDD*SSRI had a larger capillary area and more NPCs versus MDDs (p = .034 and p = .008, respectively) and control subjects (p = .010 and p = .002, respectively) in the whole DG, more NPCs in the anterior (pes, p = .042) and central (midbody, p = .004) DG, and greater capillary area in the pes (p = .002) and midbody (p = .021). The NPC number and capillary area correlated positively in the whole sample (R2 = .454, p < .001) and in treated subjects (R2 = .749, p = .001). We found no NPCs or antidepressant-related angiogenesis in CA1 and parahippocampal gyrus. The DG volume correlated positively with NPC number (p = .004) and capillary area (p < .001) and differed between groups in whole hippocampus (p = .013) and midbody (p = .036). Age negatively correlated with NPC number (p = .042), capillary area (p = .037), and bifurcations (p = .030). No gender effect was detected.

Conclusions: Antidepressants increase human hippocampal NPCs and angiogenesis selectively in the anterior and mid DG. These results raise the possibility of a causal relationship between angiogenesis and neurogenesis, as seen in other proliferating tissues, and support their possible role in the mechanism of action of antidepressants.

Figure 1. Immunohistochemistry for nestin in the human hippocampus

A: Nestin-immunoreactive cells and capillaries (in brown) were found in the subgranular zone (SGZ), usually clustered at the junction of the upper and lower blade of the DG. The dentate gyrus (DG) granule cells are stained for Nissl with Cresyl Violet. Blood vessels (in brown) show their characteristic morphology. B: Nestin-immunoreactive cell next to a capillary. Nestin-immunoreactive cells exhibit their characteristic multipolar appearance. C: Nestin- immunoreactive vessels sectioned perpendicularly to their longitudinal axis. Nestin-immunoreactive cell shows immunostained perikarya and multiple processes, including some touching the blood vessels.

Figure 2. Confocal images of nestin/Ki-67/DAPI immunofluorescence in the human dentate gyrus

A: Nestin-immunoreactive (green) neural progenitor cell (NPC) in the subgranular zone (SGZ), its dendrites are also labeled with nestin. The NPC nucleus labels for Ki-67 and DAPI (purple) showing it is in mitosis (red arrow). Another mitotic nucleus in the SGZ (white arrow) labels for Ki-67 and DAPI (purple) but not nestin, suggesting it is a mitotic cell that is not an amplifying NPC; its phenotype is unknown. Nestin also stains capillaries (green) and one shows a cell nucleus stained with DAPI (blue) inside of it. Ki-67 also labels endothelial cells undergoing regular cell division (yellow arrow). All cell nuclei stain with DAPI (blue), as seen in the granule cell layer (GCL). Co-labeling was confirmed by acquiring z-stacks at 1-μm intervals and creating orthogonal views. Lateral views of the same cell are visible in the inserts demonstrating the co-localization of nestin and Ki-67. B: Two cell nuclei stained for Ki-67 (red). C: Nestin-immunoreactive cell (green), and capillary portions. NPC dendrites are also stained for nestin and touch the capillary. D: Cell nuclei stained with DAPI in the GCL and in a vessel (white arrow)

Figure 3. Nestin/PECAM/DAPI and nestin/collagen-IV/DAPI immunofluorescence triple labeling of the human dentate gyrus

A: Nestin (green) and PECAM (or CD31, red) labeling of capillaries and endothelial cells in the subgranular zone (SGZ). Endothelial cells labeled by PECAM (red) are seen inside a capillary stained with nestin (green). Nuclei stain with DAPI (blue) and are visible in the granule cell layer (GCL) and inside the capillary (possibly the nucleus of an endothelial cell). Co-labeling was confirmed by acquiring z-stacks at 1-μm intervals and creating orthogonal views. B: Endothelial cells labeled by CD31 (red); C: Nestin labels a capillary; D: Nuclei stained with DAPI (blue) in the GCL and capillary (arrow); E: Collagen IV co-localizes in the vasculature with nestin (yellow), further confirming the vascular localization of nestin. Examples of vessels where nestin is expressed on portions of the vessel (red, arrows) that do not express collagen IV (green), confirming that nestin, but not collagen IV is expressed in remodeling capillaries. Nuclei are stained with DAPI (blue). Co-labeling was confirmed by acquiring z-stacks at 1-μm intervals and creating orthogonal views. F: Vessels stained with nestin (red); C: Vessels stained with collagen IV (green); D: Nuclei stained with DAPI (blue); some show an elongated shape, and are probably nuclei of endothelial cells as they are inside a vessel (arrows in H, G, F).

Figure 4. Nestin-immunoreactive cells and vessels in the dentate gyrus from an untreated subject with major depression (MDD) and an MDD treated with antidepressants

The fluoxetine-treated MDD (in A) shows more prominent nestin-immunoreactive cells, processes, and capillaries (in brown) compared with the untreated MDD (in B). Granule cells and glia are stained for Nissl with Cresyl violet. The subgranular zone (SGZ), granule cell layer (GCL) and molecular layer (ML) are indicated. A: 28-year-old female with MDD treated with fluoxetine (positive toxicology and antidepressant prescription in the three months prior to death). Nestin-immunoreactive cells are visible in the SGZ (black arrow) showing a multipolar morphology, and in the GCL (red arrow) showing a bipolar morphology. Nestin-immunoreactive vessels are present in the neurogenic niche. B: 33-year-old female with MDD who was not on medication (clear toxicology and no antidepressant prescription in the three months prior to death). Vessels are much less prominent and nestin-immunoreactive cells are not visible in this part of the DG.