Antipsychotic pathway genes with expression altered in opposite direction by antipsychotics and amphetamine

Cathepsin K: The Action in and Beyond Bone

Cathepsin K (CatK) is one of the most potent proteases in lysosomal cysteine proteases family, of which main function is to mediate bone resorption. Currently, CatK is among the most attractive targets for anti-osteoporosis drug development. Although many pharmaceutical companies are working on the development of selective inhibitors for CatK, there is no FDA approved drug till now. Odanacatib (ODN) developed by Merck & Co. is the only CatK inhibitor candidate which demonstrated high therapeutic efficacy in patients with postmenopausal osteoporosis in Phase III clinical trials. Unfortunately, the development of ODN was finally terminated due to the cardio-cerebrovascular adverse effects. Therefore, it arouses concerns on the undesirable CatK inhibition in non-bone sites. It is known that CatK has far-reaching actions throughout various organs besides bone. Many studies have also demonstrated the involvement of CatK in various diseases beyond the musculoskeletal system. This review not only summarized the functional roles of CatK in bone and beyond bone, but also discussed the potential relevance of the CatK action beyond bone to the adverse effects of inhibiting CatK in non-bone sites.

The Role of Cathepsins in Memory Functions and the Pathophysiology of Psychiatric Disorders

Cathepsins are proteases with functions in cellular homeostasis, lysosomal degradation and autophagy. Their role in the development of neurodegenerative diseases has been extensively studied. It is well established that impairment of proper cathepsin function plays a crucial role in the pathophysiology of neurodegenerative diseases, and in recent years a role for cathepsins in mental disorders has emerged given the involvement of cathepsins in memory function, hyperactivity, and in depression- and anxiety-like behavior. Here we review putative cathepsin functions with a special focus on their role in the pathophysiology of psychiatric diseases. Specifically, cathepsins are crucial for maintaining cellular homeostasis, particularly as part of the autophagy machinery of neural strategies underlying acute stress response. Disruption of cathepsin functions can lead to psychiatric diseases such as major depressive disease (MDD), bipolar disorder, and schizophrenia. Specifically, cathepsins can be excreted via a process called secretory autophagy. Thereby, they are able to regulate extracellular factors such as brain-derived neurotrophic factor and perlecan c-terminal fragment LG3 providing maintenance of neuronal homeostasis and mediating neuronal plasticity in response to acute stress or trauma. In addition, impairment of proper cathepsin function can result in impaired synaptic transmission by compromised recycling and biogenesis of synaptic vesicles. Taken together, further investigations on cathepsin functions and stress response, neuroplasticity, and synaptic transmission will be of great interest in understanding the pathophysiology of psychiatric disorders.

Function of Cathepsin K in the Central Nervous System of Male Mice is Independent of Its Role in the Thyroid Gland

Cathepsin K deficiency in male mice (Ctsk^-/-) results in decreased numbers of hippocampal astrocytes and altered neuronal patterning as well as learning and memory deficits. Additionally, cathepsin K carries essential roles in the thyroid gland where it contributes to the liberation of thyroid hormones (TH). Because TH are essential for brain development, in particular for the cerebellum, we investigated whether cathepsin K's function in the thyroid is directly linked to the brain phenotype of Ctsk^-/- mice. Serum levels of thyroid stimulating hormone, brain concentrations of free TH, and deiodinase 2 (Dio2) activity in brain parenchyma as well as cerebellar development were comparable in Ctsk^-/- and WT animals, suggesting regular thyroid states and TH metabolism. Despite unaltered transcript levels, protein expression of two TH transporters was enhanced in specific brain regions in Ctsk^-/- mice, suggesting altered TH supply to these regions. Thyrotropin releasing hormone (Trh) mRNA levels were enhanced threefold in the hippocampus of Ctsk^-/- mice. In the striatum of Ctsk^-/- mice the mRNA for Dio2 and hairless were approximately 1.3-fold enhanced, while mRNA levels for monocarboxylate transporter 8 and Trh were reduced to 60% and 40%, respectively, pointing to altered striatal physiology. We conclude that the role of cathepsin K in the thyroid gland is not directly associated with its function in the central nervous system (CNS) of mice. Future studies will show whether the brain region-specific alterations in Trh mRNA may eventually result in altered neuroprotection that could explain the neurobehavioral defects of Ctsk^-/- mice.

G protein-coupled receptor kinase 6/β-arrestin 2 system in a rat model of dopamine supersensitivity psychosis

In humans, long-term antipsychotic treatment is known to induce movement disorders and a psychosis, called dopamine supersensitivity psychosis (DSP). The mechanism by which chronic administration of antipsychotic(s) causes DSP may be the treatment-induced up-regulation of dopamine D2 receptors (DRD2). G protein-coupled receptor kinase 6 (GRK6) and beta-arrestin 2 (ARRB2) play important roles in the trafficking of DRD2 by phosphorylation and internalization. We investigated the effects of chronic continuous treatment with mini-pump-administered haloperidol (HAL) on the sensitivity of Wistar rats to dopamine, as measured by the locomotor response to methamphetamine (MAP) and the density of striatal DRD2. Chronic continuous treatment with HAL resulted in significantly higher locomotor response to MAP and significantly higher striatal DRD2 density compared with those in rats administered vehicle (VEH). Enzyme-linked immunosorbent assays revealed that striatal ARRB2 in DSP model rats tended to decrease in comparison with that in the VEH group. In addition, the ratio of GRK6/ARRB2 in DSP model rats was significantly higher than that in controls. Our results suggest that alterations of the GRK6 and ARRB2 system could induce both DRD2 up-regulation and impairment of the dopamine signaling pathway, resulting potentially in the development of DSP.

Cathepsin K: a unique collagenolytic cysteine peptidase

Cathepsin K has emerged as a promising target for the treatment of osteoporosis in recent years. Initially identified as a papain-like cysteine peptidase expressed in high levels in osteoclasts, the important role of this enzyme in bone metabolism was highlighted by the finding that mutations in the CTSK gene cause the rare recessive disorder pycnodysostosis, which is characterized by severe bone anomalies. At the molecular level, the physiological role of cathepsin K is reflected by its unique cleavage pattern of type I collagen molecules, which is fundamentally different from that of other endogenous collagenases. Several cathepsin K inhibitors have been developed to reduce the excessive bone matrix degradation associated with osteoporosis, with the frontrunner odanacatib about to successfully conclude Phase 3 clinical trials. Apart from osteoclasts, cathepsin K is expressed in different cell types throughout the body and is involved in processes of adipogenesis, thyroxine liberation and peptide hormone regulation. Elevated activity of cathepsin K has been associated with arthritis, atherosclerosis, obesity, schizophrenia, and tumor metastasis. Accordingly, its activity is tightly regulated via multiple mechanisms, including competitive inhibition by endogenous macromolecular inhibitors and allosteric regulation by glycosaminoglycans. This review provides a state-of-the-art description of the activity of cathepsin K at the molecular level, its biological functions and the mechanisms involved in its regulation.

Association study of common variants within the G protein-coupled receptor kinase 6 gene and schizophrenia susceptibility in Han Chinese

In this study, we examined whether common variants in the G protein-coupled receptor kinase 6 gene (GRK6) confers susceptibility to schizophrenia in Chinese. We genotyped two common variants in 697 schizophrenia patients and 563 healthy control subjects. No significant difference in either allele or genotype comparisons between the case and control groups was found. Our results imply that GRK6 may not play a role in the pathophysiology of schizophrenia among Han Chinese.

A gene expression and systems pathway analysis of the effects of clozapine compared to haloperidol in the mouse brain implicates susceptibility genes for schizophrenia

Clozapine has markedly superior clinical properties compared to other antipsychotic drugs but the side effects of agranulocytosis, weight gain and diabetes limit its use. The reason why clozapine is more effective is not well understood. We studied messenger RNA (mRNA) gene expression in the mouse brain to identify pathways changed by clozapine compared to those changed by haloperidol so that we could identify which changes were specific to clozapine. Data interpretation was performed using an over-representation analysis (ORA) of gene ontology (GO), pathways and gene-by-gene differences. Clozapine significantly changed gene expression in pathways related to neuronal growth and differentiation to a greater extent than haloperidol; including the microtubule-associated protein kinase (MAPK) signalling and GO terms related to axonogenesis and neuroblast proliferation. Several genes implicated genetically or functionally in schizophrenia such as frizzled homolog 3 (FZD3), U2AF homology motif kinase 1 (UHMK1), pericentriolar material 1 (PCM1) and brain-derived neurotrophic factor (BDNF) were changed by clozapine but not by haloperidol. Furthermore, when compared to untreated controls clozapine specifically regulated transcripts related to the glutamate system, microtubule function, presynaptic proteins and pathways associated with synaptic transmission such as clathrin cage assembly. Compared to untreated controls haloperidol modulated expression of neurotoxic and apoptotic responses such as NF-kappa B and caspase pathways, whilst clozapine did not. Pathways involving lipid and carbohydrate metabolism and appetite regulation were also more affected by clozapine than by haloperidol.

Cathepsin K deficiency in mice induces structural and metabolic changes in the central nervous system that are associated with learning and memory deficits

Background

Cathepsin K is a cysteine peptidase known for its importance in osteoclast-mediated bone resorption. Inhibitors of cathepsin K are in clinical trials for treatment of osteoporosis. However, side effects of first generation inhibitors included altered levels of related cathepsins in peripheral organs and in the central nervous system (CNS). Cathepsin K has been recently detected in brain parenchyma and it has been linked to neurobehavioral disorders such as schizophrenia. Thus, the study of the functions that cathepsin K fulfils in the brain becomes highly relevant.

Results

Cathepsin K messenger RNA was detectable in all brain regions of wild type (WT) mice. At the protein level, cathepsin K was detected by immunofluorescence microscopy in vesicles of neuronal and non-neuronal cells throughout the mouse brain. The hippocampus of WT mice exhibited the highest levels of cathepsin K activity in fluorogenic assays, while the cortex, striatum, and cerebellum revealed significantly lower enzymatic activities. At the molecular level, the proteolytic network of cysteine cathepsins was disrupted in the brain of cathepsin K-deficient (Ctsk^-/-) animals. Specifically, cathepsin B and L protein and activity levels were altered, whereas cathepsin D remained largely unaffected. Cystatin C, an endogenous inhibitor of cysteine cathepsins, was elevated in the striatum and hippocampus, pointing to regional differences in the tissue response to Ctsk ablation. Decreased levels of astrocytic glial fibrillary acidic protein, fewer and less ramified profiles of astrocyte processes, differentially altered levels of oligodendrocytic cyclic nucleotide phosphodiesterase, as well as alterations in the patterning of neuronal cell layers were observed in the hippocampus of Ctsk^-/- mice. A number of molecular and cellular changes were detected in other brain regions, including the cortex, striatum/mesencephalon, and cerebellum. Moreover, an overall induction of the dopaminergic system was found in Ctsk^-/- animals which exhibited reduced anxiety levels as well as short- and long-term memory impairments in behavioral assessments.

Conclusion

We conclude that deletion of the Ctsk gene can lead to deregulation of related proteases, resulting in a wide range of molecular and cellular changes in the CNS with severe consequences for tissue homeostasis. We propose that cathepsin K activity has an important impact on the development and maintenance of the CNS in mice.

Dopaminergic activity in depressed smokers: a positron emission tomography study

Tobacco dependence is highly prevalent in depressed patients. We assessed changes in [(11)C]-raclopride binding potential (BP) using positron emission tomography (PET) before and after the oral administration of d-amphetamine in healthy controls and unmedicated patients with current depression with and without current tobacco dependence. Over a single study day 2 [(11)C]-raclopride positron emission tomography scans were taken in 38 subjects: at baseline and 2 h following oral d-amphetamine 30 mg. Twenty controls (9 smokers, 11 nonsmokers) and 18 subjects with current major depressive episode (8 smokers, 10 non-smokers). Striatal [(11)C]-raclopride binding potential was measured before and after d-amphetamine administration. Depressed smokers had a lower baseline [(11)C]-raclopride binding potential compared with both control non-smokers (P < 0.007) and depressed non-smokers (P < 0.001). There was a main effect of smoking status on amphetamine-induced change in [(11)C]-raclopride binding potential (P < 0.02), but no main effect of depression. This may be due to a floor effect because of the low BP at baseline. Depressed subjects reported significant increase of positive mood after d-amphetamine administration compared with controls (depressed smokers vs. control smokers: P < 0.05; depressed non-smokers vs. controls: P < 0.055). Tobacco dependence appears to decrease d-amphetamine-induced changes in [(11)C]-raclopride binding potential as measured by positron emission tomography. Comorbid major depression and tobacco dependence exacerbates this effect, suggesting an altered dopamine system in comorbid patients.

The amphetamine-induced sensitized state as a model of schizophrenia

Schizophrenia is a serious psychiatric disorder which impacts a broad range of cognitive, behavioural and emotional domains. In animals, exposure to an intermittent, escalating dose regimen of amphetamine induces a sensitized state that appears to share a number of behavioural and neurochemical similarities with schizophrenia. In humans repeated exposure to amphetamine, or other psychomotor stimulants, can induce sensitization as well as psychosis. The following paper evaluates the evidence for the amphetamine-induced sensitized state as an animal model of schizophrenia, focussing separately on the positive, cognitive and negative symptoms associated with this disease. Current evidence supports the use of amphetamine sensitization as a model of the positive symptoms observed in schizophrenia. Additionally, there is increasing evidence for long-lasting cognitive deficits in sensitized animals, especially in the area of attention and/or cognitive flexibility. Other areas of cognition, such as long-term memory, appear to be unaltered in sensitized animals. Finally, little evidence currently exists to either support or refute the use of amphetamine sensitization as a model of negative symptoms. It is concluded that amphetamine sensitization likely impacts behaviour by altering the functioning of mesolimbic dopamine systems and prefrontal cortical function and can serve as a model of certain domains of schizophrenia.

Olanzapine increases RGS7 protein expression via stimulation of the Janus tyrosine kinase-signal transducer and activator of transcription signaling cascade

Atypical antipsychotics such as olanzapine have high affinity for multiple monoamine neurotransmitter receptors and are the mainstay of pharmacological therapy for treatment of schizophrenia. In addition to blocking monoamine receptors, these drugs also affect intracellular signaling cascades. We now report that 24-h treatment with 300 nM olanzapine causes desensitization of serotonin (5-HT)(2A) receptors in A1A1v cells, a rat cortical cell line, as indicated by a reduction in inositol phosphate accumulation following stimulation with a 5-HT(2A/2C) receptor agonist (-)-1-(2,5-dimethoxy-4-lodophenyl)-2-aminopropane HCl. Olanzapine treatment for 24 h increased the levels of 5-HT(2A) receptors in both cytosol (234 +/- 34% of control level) and membrane fractions (206 +/- 14% of control levels) and RGS7 proteins in both cytosol (193 +/- 32% of control levels) and membrane fractions (160 +/- 18% of control levels) as measured on Western blots. Increased phosphorylation of Janus tyrosine kinase (JAK) 2 and increased phosphorylation and nuclear translocation of signal transducer and activator of transcription (STAT) 3 with 24-h olanzapine treatment demonstrate activation of the JAK-STAT signaling cascade. Pretreatment with a JAK inhibitor, AG490 [alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide], prevented the olanzapine-induced increase in membrane RGS7 protein levels; AG490 alone had no effect on RGS7 protein levels. We verified that treatment with AG490 reduced phosphorylation of JAK2 and inhibited the nuclear localization of phospho-STAT3. Interestingly, treatment with the JAK inhibitor had no effect on 5-HT(2A) receptor protein levels. These data suggest that olanzapine-induced activation of the JAK-STAT signaling cascade causes increased expression of RGS7 protein, which in turn could mediate desensitization of 5-HT(2A) receptor signaling caused by olanzapine because RGS7 binds to Galpha(q) protein and accelerates GTP hydrolysis.

Amphetamine sensitization elevates CaMKIIß mRNA

Recent studies have shown that the elevation in calcium/calmodulin-dependent protein kinase II (CaMKII) may play an important role in amphetamine-induced dopamine release, as well as in the increase of dopamine D2 receptor high-affinitystates in psychosis. Because amphetamine sensitization is a widely used animal model of psychosis or schizophrenia, we investigated whether amphetamine sensitization results in an overall increase in the alpha and beta subunits of CaMKII. To answer this question, we measured CaMKII alpha and beta subunit mRNA expression using Real-Time Quantitative PCR in amphetamine-sensitized rat striata, compared to saline-treated controls. The results were then standardized to beta-glucuronidase, a housekeeping gene. Our results showed a statistically significant increase in the CaMKII beta subunit, and an increase in the alpha subunit which did not reach statistical significance. Because the levels of both CaMKIIbeta and CaMKIIalpha play a role in neuronal function and synapse formation, the present finding of an elevated level of CaMKII beta and alpha subunit mRNA in the amphetamine-sensitized model of psychosis points to the possibility of dysregulated levels of CaMKII subunits in human psychosis.