The regulatory effect of glucocorticoids on perineuronal nets occurs through different mechanisms: potential relationship to schizophrenia

Yue, Liang (2025) The regulatory effect of glucocorticoids on perineuronal nets occurs through different mechanisms: potential relationship to schizophrenia. PhD thesis, University of Glasgow.

Abstract

Perineuronal nets (PNNs) are extracellular matrix structures surrounding mainly parvalbumin (Pv)-expressing γ-aminobutyric acid (GABAergic) interneurons, providing several cellular or neural functions during the brain developmental period, such as maintaining cellular or synaptic connections, regulating neural plasticity, controlling the closure of critical period and protecting neurons from being damaged by external substrates. Disrupted expression of PNNs and PNN components could result in brain dysfunction, and could be observed in various brain disorders, including schizophrenia. Schizophrenia is a psychiatric disorder, affecting approximately 1% of the population worldwide. Patients diagnosed with schizophrenia exhibit positive, negative and cognitive symptoms. With regard to the aetiology of schizophrenia, genetic and environmental risk factors are associated with schizophrenia, and prenatal maternal stress is robustly detected as an environmental risk factor, roughly doubling the likelihood of the condition in offspring. How risk factors, particularly environmental stress, are associated with schizophrenia is still unclarified.

PNN and Pv-expressing neurons are one of the neuronal systems involved in the pathology of schizophrenia, with several lines of evidence that abnormalities of PNN structure and Pv expression are observed in schizophrenia. Hence a potential pathway through which stress could increase the risk of schizophrenia is by altering PNN and Pv formation or expression. There is some evidence that stress could alter the general expression and formation of PNNs and PNN components, including chondroitin sulfate proteoglycans (CSPGs) (aggrecan, brevican, neurocan, versican and phosphacan), hyaluronan synthase (Has) and link proteins (Haplns), and tenascin R (TnR). Apart from PNNs, evidence demonstrated disrupted Pv expression after stress exposure, and abnormal PNN and Pv expression, with disturbed density and intensity of staining, is observed in schizophrenia patients. Additionally, glutamate decarboxylase (Gad), a critical factor contributing to GABA synthesis, is consistently demonstrated to be disturbed in schizophrenia subjects in previous studies, supporting disrupted GABA neurotransmission in schizophrenia.

In this case, disrupted Pv, Gad and PNN components influenced by external stress might be associated with the increased risk of schizophrenia, which could be a potential pathway underlying the aetiology of schizophrenia. However, the alterations of Pv and Gad expression by stress remained controversial, and whether the expression of PNN components is affected by stress is not fully investigated. Thus, the current study aimed to investigate the effect of glucocorticoids (GCs) – likely mediators of the effects of prenatal maternal stress on the foetus -on PNN component genes, Pv and Gad expression, and further to investigate whether the altered expression was associated with schizophrenia-like changes.

In primary cultured mouse cortical neurons, the data from the current study reported that GCs could alter the gene expression of specific PNN components, including, versican (Vcan), hyaluronan synthase 1 and hyaluronan synthase 3 (Has1, Has3), Hapln4 and TnR and Pv. Altered gene expression was detected primarily at the mRNA level, with corresponding protein changes proving harder to detect. However, altered structural properties of PNNs in the cultures were detected following GC exposure, using Wisteria floribunda agglutinin (WFA) staining. Reduced length of PNNs covering neuronal dendrites was observed, indicating that expression and formation of PNNs were affected by GCs. These results confirmed the hypothesis that over-exposure to stress could disrupt the expression of some of PNN components and suppress the PNN structure.

GCs proved to be able to modify the expression of a number of different PNN component genes, but this was evident primarily at 7 days in vitro (DIV), and also at 14 DIV, but not at 21 DIV, suggesting a major modulatory effect early in development as PNNs are forming. Interestingly, the effects on PNN structure were detected at 21 DIV as well as 14 DIV, a time when no effects on PNN gene expression were observed, suggesting a distinct mechanisms of action.

The precise mechanisms involved in these GC actions appeared diverse, but difficult to identify. The suppressive effects of GCs on Vcan, Hapln4 and TnR mRNA expression appeared to occur through a non-genomic pathway, as they were rapid (detectable within 4h) and not reproduced by the mineralocorticoid agonist aldosterone, or blocked by the GR antagonist mifepristone. The possibility of a post-transcriptional action to accelerate mRNA decay was tested, but no evidence was obtained in support of this idea. The suppressive effects on Has1, Has3 and Pv were also rapid, but were sensitive to mifepristone, suggesting mediation through GRs. Mifepristone alone affected the expression of some PNN component mRNAs, including aggrecan (Acan), brevican (Bcan), neurocan (Ncan), and Has1, implying that basal (non-stressed level) GCs in the culture medium were exerting effects on these genes.

The changes in protein expression that were detected, including GC-induced deceases in the levels of Has2 and Gad65, and increased levels of Has3, TnR and Gad1 induced by mifepristone alone, appeared to occur within 4h, and in the absence of any corresponding changes in mRNA levels. The possibility that GCs might be modulating the activity of the proteasome was considered. Decreased activity was observed after GC exposure that was rapid and specific for the chymotrypsin-like activity. While this novel action cannot explain the GC-induced reduction in Has2 protein, it could contribute to the ability of mifepristone to increase PNN component protein levels in the absence of any mRNA changes. Further work should assess the ability of mifepristone alone to affect proteasome activity in these cultures.

To examine the expression of PNNs and Pv in the brain from mouse models of aspects of schizophrenia, an overview of the distributions of PNNs and Pv in various brain regions is needed. In brain sections from mice expressing Td-tomato from the GABAergic interneuron specific Nkx2.1 promoter, PNNs and Pv-expressing interneurons were largely distributed in cortical layers2/3 and layers 4/5, in prefrontal cortex (PFC) and retrosplenial granular cortex. No sex differences in PNN expression were detected. PFC is an important cortical region regulating executive functions and associated with various abnormal behaviours in schizophrenia. Since duplications of chr.16p11.2 are one of the strongest genetic variants associated with schizophrenia, Pv, PNN component and Gad expression gene expression was assessed in wild-type mice and 16p11.2 duplication mice, both without and with an environmental risk factor manipulation, specifically, maternal immune activation (MIA). Similar changes in Pv and CSPG component expression were observed in MIA-exposed adult offspring in both conditions with dams or littermates as experimental units. The expression of CSPG genes was elevated by MIA, as opposed to the decreases observed with GC exposure in vitro. No overt effects of the genetic manipulation were observed, nor interactions with the MIA.

Taken together, the data presented in the current study suggested that GCs could suppress expression of Pv, several PNN component genes, and PNN morphology, and the altered Pv and CSPG expression were also caused by MIA. A remarkable diversity of GC effects on PNN component gene expression were observed, acting on multiple targets, utilizing a number of different mechanisms, and with clear developmental regulation. The results indicated that external and prenatal stressors might be associated with the increased risk of schizophrenia by disrupting PNN and Pv expression. However, to fully investigate the underlying mechanisms and their relationship to the pathology of schizophrenia, these alterations in the function of PNNs and Pv need to be further investigated.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: R Medicine > RC Internal medicine > RC0321 Neuroscience. Biological psychiatry. Neuropsychiatry
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Psychology & Neuroscience
• Supervisor's Name: Morris, Professor Brian
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85260
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 26 Jun 2025 13:42
• Last Modified: 26 Jun 2025 13:45
• Thesis DOI: 10.5525/gla.thesis.85260
• URI: https://theses.gla.ac.uk/id/eprint/85260