Suwarna Chakraborty

Dysregulated dopamine (DA) signaling and redox homeostasis contributes to multiple neuropsychiatric and neurodegenerative disorders. Polymorphisms that influence the activity of catechol-O-methyltransferase (COMT), an enzyme critical for degrading DA in the dorsolateral prefrontal cortex, have been implicated in behavioral and neuropsychiatric alterations associated with schizophrenia (SCZ). Adverse neuropsychiatric effects have also been reported in Parkinson’s disease (PD) patients administered COMT inhibitors in combination with other DA-enhancing therapies. COMT exists as two isoforms: a soluble short isoform (S-COMT) and a membrane-bound long isoform (MB-COMT). These variants differ in their N-terminal domains, with MB-COMT being the predominant brain isoform. Here, unbiased proteomic and biochemical analyses show that genetic loss of MB-COMT disrupts DA signaling and perturbs pathways governing synaptic and mitochondrial function, iron and copper homeostasis, and redox balance. Limited proteolysis mass spectrometry (LiP-MS) further revealed that MB-COMT deficiency triggers widespread protein structural alterations, a molecular event commonly occurring in neurodegenerative conditions but not as well studied in neuropsychiatric diseases. Our results show that MB-COMT is a molecular hub that connects multiple cellular pathways whose differential dysregulation underlies the pathophysiology of complex neuropsychiatric diseases such as SCZ. Thus, MB-COMT is identified as a key regulator of brain DA biology, loss of which activates cellular stress response pathways, revealing potential targets for therapeutic intervention.

Deterioration of the blood–brain barrier (BBB), including impaired neurovascular uncoupling, contributes to cognitive decline in aging. The BBB is formed principally by brain microvascular endothelial cells (ECs), and ECs throughout the body are enriched for the transcription factor Krüppel-like factor 4 (KLF4). Because KLF4 levels in ECs decrease with age, we tested whether that decline contributes to aging-related BBB deterioration, neurovascular dysfunction, and cognitive impairment. Using EC-specific Klf4 knockout mice (EC-K4KO), we show that loss of EC KLF4 accelerates multiple age-related brain pathologies. Indeed, middle-aged EC-K4KO mice display pathological features that are not normally observed until advanced age, including marked BBB leakage, impaired neurovascular coupling, loss of microvessels, increased oxidative damage, neuroinflammation, neurodegeneration, anxiety-like behavior, and cognitive deficits. Single-cell RNA sequencing of brain vasculature reveals dysregulation of immune response and barrier-related genes in ECs lacking KLF4, indicating that KLF4 maintains brain endothelial homeostasis by constraining proinflammatory and senescence programs at the chromatin level. Together, these results identify loss of EC KLF4 as a key driver of neurovascular decline and age-associated cognitive dysfunction.

Rationale Anxiety is one of the most comorbid conditions with major depressive disorder (MDD). Depression-associated anxiety often stems from the dysfunctional hypothalamic-pituitary-adrenal (HPA) axis and its altered regulation by the amygdala. Furthermore, MDD is associated with altered glutamatergic processing leading to anxiety and impaired regulation of the HPA axis. Recent studies have demonstrated that N-acetyl cysteine (NAC), a pleiotropic drug, exerts antidepressant-like effect by modulation of hippocampal functions, periterminal release of glutamate, and/or redox systems. However, the effects of NAC on depression-associated anxiety, HPA axis hyperactivity, and amygdalar dysfunctions are relatively unknown. Objectives Accordingly, we evaluated the effect of NAC on neonatal clomipramine (CLI)-induced adulthood anxiety and accompanying changes in plasma corticosterone levels, amygdalar volumes, neuronal/glial densities, levels of monoamines, and their metabolites in the amygdalar complex. Results We found that chronic treatment with NAC reverses CLI-induced anhedonia and enhanced anxiety. Interestingly, attenuation of CLI-associated anxiety in NAC-treated rats were accompanied by a reversal of adrenal and spleen hypertrophy, and normalization of enhanced plasma corticosterone levels, indicating improved HPA axis functioning. Furthermore, NAC treatment was sufficient to reverse volumetric hypertrophy of basolateral amygdala (BLA), and altered noradrenaline (NA) metabolism in the amygdalar complex. The effects of NAC in the reversal of CLI-induced impairments were similar to that of fluoxetine (FLX). Conclusions We suggest that beneficial effects of NAC on antidepressive- and antianxiety-like behaviors are at least in part mediated via restoration of amygdalar and HPA axis functioning. Our results support the hypothesis that NAC might be evolved as a therapeutic strategy for reversal of amygdalar dysfunction in depression.

Repeated stress causes cognitive decline and decreases the expression of glial fibrillary acidic protein (GFAP)⁺ astroglial cells in the prefrontal cortex (PFC). The stress-induced alterations in astroglial density and morphology might significantly contribute to cognitive impairments. Apart from PFC, a key region involved in modulation of repercussions of stress is basolateral amygdala (BLA), which undergoes hypertrophy following chronic immobilization stress (CIS) and has intense reciprocal connections to the PFC. Interestingly, inactivation of BLA precludes stress-induced learning deficits. However, the modulatory role of BLA on CIS-induced alterations in GFAP⁺ astroglial density and associated learning deficits are presently unknown. Accordingly, we present two sets of experiments evaluating the effects of BLA inactivation either permanently or temporarily on CIS-induced changes in learning and astroglial expression in the PFC. CIS causes impairment in novel object recognition memory and astroglial loss in the PFC. In experiment I, we permanently inactivated the BLA by ibotenate lesion prior to CIS and observed a significant improvement in learning. Surprisingly, BLA lesion also prevented the stress-induced astroglial loss in the PFC. Furthermore, in the experiment II, we analyzed whether the effects of permanent inactivation could be mirrored by the temporary blockage of BLA specifically during stress. Interestingly, temporary inactivation of BLA mimics the effects of lesion. There was a notable prevention of learning impairment and astroglial loss in the PFC following BLA inactivation during stress. The present study emphasizes that stress-induced astroglial loss might contribute to cognitive deficits and modulation of BLA activity might be a viable strategy for management of stress-related PFC dysfunctions.