Extracellular matrix-glial abnormalities in the amygdala and entorhinal cortex of subjects diagnosed with schizophrenia

Abstract

Context: Chondroitin sulfate proteoglycans (CSPGs), a main component of the brain extracellular matrix, regulate developmental and adult neural functions that are highly relevant to the pathogenesis of schizophrenia. Such functions, together with marked expression of CSPGs in astrocytes within the normal human amygdala and evidence of a disruption of astrocytic functions in this disease, point to involvement of CSPG-glial interactions in schizophrenia.

Hypothesis: Chondroitin sulfate proteoglycan-related abnormalities involve glial cells and extracellular matrix pericellular aggregates (perineuronal nets) in the amygdala and entorhinal cortex of subjects with schizophrenia.

Design: Postmortem case-control study.

Setting: The Translational Neuroscience Laboratory at McLean Hospital, Harvard Medical School. Specimens were obtained from the Harvard Brain Tissue Resource Center at McLean Hospital.

Participants: Two separate cohorts of healthy control (n = 15; n = 10) and schizophrenic (n = 11; n = 10) subjects and a cohort of subjects with bipolar disorder (n = 11).

Interventions: Quantitative, immunocytological, and histological postmortem investigations.

Main outcome measures: Numerical densities of CSPG-positive glial cells and perineuronal nets, glial fibrillary acidic protein-positive astrocytes, and total numbers of parvalbumin-positive neurons in the deep amygdala nuclei and entorhinal cortex.

Results: In schizophrenia, massive increases in CSPG-positive glial cells were detected in the deep amygdala nuclei (419%-1162%) and entorhinal cortex (layer II; 480%-1560%). Perineuronal nets were reduced in the lateral nucleus of the amygdala and lateral entorhinal cortex (layer II). Numerical densities of glial fibrillary acidic protein-positive glial cells and total numbers of parvalbumin-positive neurons were unaltered. Changes in CSPG-positive elements were negligible in subjects with bipolar disorder.

Conclusions: Marked changes in functionally relevant molecules in schizophrenia point to a pivotal role for extracellular matrix-glial interactions in the pathogenesis of this disease. Disruption of these interactions, unsuspected thus far, may represent a unifying factor contributing to disturbances of neuronal migration, synaptic connectivity, and GABAergic, glutamatergic, and dopaminergic neurotransmission in schizophrenia. The lack of CSPG abnormalities in bipolar disorder points to a distinctive aspect of the pathophysiology of schizophrenia in key medial temporal lobe regions.

Figure 1

Marked increase in Wisteria floribunda agglutinin (WFA)–labeled elements in subjects with schizophrenia. Photographic composites show sample coronal sections, labeled histochemically with WFA (black reaction product), containing the amygdala nuclei and entorhinal cortex (ECx) from a healthy control subject (A) and a subject with schizophrenia (B). Note the markedly increased WFA labeling in the subject with schizophrenia. Dashed lines (A) indicate the borders of each region. C, A detailed image of the regions is shown. E and D, Photomicrographs show a portion of the superficial layers of the ECx (segment shown in E corresponds to that marked by arrows in B). F, G, H, and I, Portions of the superficial layers of lateral ECx are shown for matched pairs of healthy controls and subjects with schizophrenia. Note the distribution of perineuronal nets in the control subjects, which is typically more dorsal with respect to WFA-labeled glial cells. AA indicates anterior nucleus of the amygdala; ABN, accessory basal nucleus of the amygdala; BN, basal nucleus of the amygdala; CE, central nucleus of the amygdala; CO, cortical nucleus of the amygdala; HP, hippocampus; LN, lateral nucleus of the amygdala; LV, lateral ventrical; PRCx, perirhinal cortex.

Figure 2

Wisteria floribunda agglutinin (WFA)–labeled glial cells are increased in deep amygdala nuclei and entorhinal cortex (ECx) (layer II) in subjects with schizophrenia. Numerical densities (Nd) (cells/mm³; logarithmic transformation) of WFA-labeled glial cells (A and B) and glial fibrillary acidic protein (GFAP)–positive cells (C and D) in deep amygdala nuclei (A and C) and ECx (layer II; B and D) of control subjects and subjects with schizophrenia and bipolar disorder. Significance values are derived from a stepwise linear regression process. Scatterplots show the mean (bar) and 95% confidence intervals of the mean (error bars); dashed lines represent the total response sample mean. IR indicates immunoreactive.

Figure 3

Enzymatic treatment with chondroitinase ABC eliminates Wisteria floribunda agglutinin (WFA) labeling in perineuronal nets (PNNs) and glial cells. Photomicrographs show neuronal clusters in layer II of the entorhinal cortex in sections processed for WFA (black reaction product) and counterstained in a control subject (A and B) and a subject with schizophrenia (C and D). B and D, Sections were treated with chondroitinase ABC prior to WFA histochemistry. This treatment ablated WFA labeling of PNNs and glial cells. Note that in the untreated control (A), WFA mainly labeled PNNs (arrow) while WFA-positive glial cells are less frequent. In the untreated sections from a subject with schizophrenia (C), PNNs are reduced, while WFA-labeled glial cells (arrow) are increased.

Figure 4

Wisteria floribunda agglutinin (WFA)–labeled perineuronal nets (PNNs) are decreased in the lateral nucleus and layer II of the lateral entorhinal cortex (ECx-L) in subjects with schizophrenia. Numerical densities (Nd) (cells/mm³) of WFA-labeled PNNs (A and B) and numerical densities and total numbers of parvalbumin-positive neurons in the amygdala (C and D). Logarithmic transformation was applied to all values. Significance values are derived using stepwise linear regression process. Scatter plots show the mean (bar) and 95% confidence intervals of the mean (error bars); dashed lines represent the total response sample mean. IR indicates immunoreactive.