Antidepressants and Cdk inhibitors: releasing the brake on neurogenesis?

Pharmacological Enhancement of Adult Hippocampal Neurogenesis Improves Behavioral Pattern Separation in Young and Aged Male Mice

Background

Impairments in behavioral pattern separation (BPS)-the ability to distinguish between similar contexts or experiences-contribute to memory interference and overgeneralization seen in many neuropsychiatric conditions, including depression, anxiety, posttraumatic stress disorder, dementia, and age-related cognitive decline. Although BPS relies on the dentate gyrus and is sensitive to changes in adult hippocampal neurogenesis, its significance as a pharmacological target has not been tested.

Methods

In this study, we applied a human neural stem cell high-throughput screening cascade to identify compounds that increase human neurogenesis. One compound with a favorable profile, RO6871135, was then tested in young and aged mice for effects on BPS and anxiety-related behaviors.

Results

Chronic treatment with RO6871135 (7.5 mg/kg) increased adult hippocampal neurogenesis and improved BPS in a fear discrimination task in both young and aged mice. RO6871135 treatment also lowered innate anxiety-like behavior, which was more apparent in mice exposed to chronic corticosterone. Ablation of adult hippocampal neurogenesis by hippocampal irradiation supported a neurogenesis-dependent mechanism for RO6871135-induced improvements in BPS. To identify possible mechanisms of action, in vitro and in vivo kinase inhibition and chemical proteomics assays were performed. These tests indicated that RO6871135 inhibited CDK8, CDK11, CaMKIIa, CaMKIIb, MAP2K6, and GSK-3β. An analog compound also demonstrated high affinity for CDK8, CaMKIIa, and GSK-3β.

Conclusions

These studies demonstrate a method for empirical identification and preclinical testing of novel neurogenic compounds that can improve BPS and point to possible novel mechanisms that can be interrogated for the development of new therapies to improve specific endophenotypes such as impaired BPS.

Shared genetic architecture and bidirectional clinical risks within the psycho-metabolic nexus

BACKGROUND

Increasing evidence suggests a complex interplay between psychiatric disorders and metabolic dysregulations. However, most research has been limited to specific disorder pairs, leaving a significant gap in our understanding of the broader psycho-metabolic nexus.

METHODS

This study leveraged large-scale cohort data and genome-wide association study (GWAS) summary statistics, covering 8 common psychiatric disorders and 43 metabolic traits. We introduced a comprehensive analytical strategy to identify shared genetic bases sequentially, from key genetic correlation regions to local pleiotropy and pleiotropic genes. Finally, we developed polygenic risk score (PRS) models to translate these findings into clinical applications.

FINDINGS

We identified significant bidirectional clinical risks between psychiatric disorders and metabolic dysregulations among 310,848 participants from the UK Biobank. Genetic correlation analysis confirmed 104 robust trait pairs, revealing 1088 key genomic regions, including critical hotspots such as chr3: 47588462-50387742. Cross-trait meta-analysis uncovered 388 pleiotropic single nucleotide variants (SNVs) and 126 shared causal variants. Among variants, 45 novel SNVs were associated with psychiatric disorders and 75 novel SNVs were associated with metabolic traits, shedding light on new targets to unravel the mechanism of comorbidity. Notably, RBM6, a gene involved in alternative splicing and cellular stress response regulation, emerged as a key pleiotropic gene. When psychiatric and metabolic genetic information were integrated, PRS models demonstrated enhanced predictive power.

INTERPRETATION

The study highlights the intertwined genetic and clinical relationships between psychiatric disorders and metabolic dysregulations, emphasising the need for integrated approaches in diagnosis and treatment.

FUNDING

The National Key Research and Development Program of China (2023YFC2506200, SHH). The National Natural Science Foundation of China (82273741, SY).

Pharmacological Enhancement of Adult Hippocampal Neurogenesis Improves Behavioral Pattern Separation in Young and Aged Mice

BACKGROUND

Impairments in behavioral pattern separation (BPS)-the ability to distinguish between similar contexts or experiences-contribute to memory interference and overgeneralization seen in many neuropsychiatric conditions, including depression, anxiety, PTSD, dementia, and age-related cognitive decline. While BPS relies on the dentate gyrus and is sensitive to changes in adult hippocampal neurogenesis (AHN), its significance as a pharmacological target has not been tested.

METHODS

In this study, we applied a human neural stem cell high-throughput screening cascade to identify compounds that increase human neurogenesis. One compound with a favorable profile, RO6871135, was then tested in BPS in mice.

RESULTS

Chronic treatment with RO6871135, 7.5 mg/kg increased AHN and improved BPS in a fear discrimination task in both young and aged mice. RO6871135 treatment also lowered innate anxiety-like behavior, which was more apparent in mice exposed to chronic corticosterone. Ablation of AHN by hippocampal irradiation supported a neurogenesis-dependent mechanism for RO6871135-induced improvements in BPS. To identify possible mechanisms of action, in vitro and in vivo kinase inhibition and chemical proteomics assays were performed. These tests indicated that RO6871135 inhibited CDK8, CDK11, CaMK2a, CaMK2b, MAP2K6, and GSK3b. An analog compound also demonstrated high affinity for CDK8, CaMK2a, and GSK3b.

CONCLUSIONS

These studies demonstrate a method for empirical identification and preclinical testing of novel neurogenic compounds that can improve BPS, and points to possible novel mechanisms that can be interrogated for the development of new therapies to improve specific endophenotypes such as impaired BPS.

Shared peripheral blood biomarkers for Alzheimer’s disease, major depressive disorder, and type 2 diabetes and cognitive risk factor analysis

Background

Alzheimer's disease (AD), type 2 diabetes mellitus (T2DM), and Major Depressive Disorder (MDD) have a higher incidence rate in modern society. Although increasing evidence supports close associations between the three, the mechanisms underlying their interrelationships remain elucidated.

Objective

The primary purpose is to explore the shared pathogenesis and the potential peripheral blood biomarkers for AD, MDD, and T2DM.

Methods

We downloaded the microarray data of AD, MDD, and T2DM from the Gene Expression Omnibus database and constructed co-expression networks by Weighted Gene Co-Expression Network Analysis to identify differentially expressed genes. We took the intersection of differentially expressed genes to obtain co-DEGs. Then, we performed GO and KEGG enrichment analysis on the common genes in the AD, MDD, and T2DM-related modules. Next, we utilized the STRING database to find the hub genes in the protein-protein interaction network. ROC curves were constructed for co-DEGs to obtain the most diagnostic valuable genes and to make drug predictions against the target genes. Finally, we conducted a present condition survey to verify the correlation between T2DM, MDD and AD.

Results

Our findings indicated 127 diff co-DEGs, 19 upregulated co-DEGs, and 25 down-regulated co-DEGs. Functional enrichment analysis showed co-DEGs were mainly enriched in signaling pathways such as metabolic diseases and some neurodegeneration. Protein-protein interaction network construction identified hub genes in AD, MDD and T2DM shared genes. We identified seven hub genes of co-DEGs, namely, SMC4, CDC27, HNF1A, RHOD, CUX1, PDLIM5, and TTR. The current survey results suggest a correlation between T2DM, MDD and dementia. Moreover, logistic regression analysis showed that T2DM and depression increased the risk of dementia.

Conclusion

Our work identified common pathogenesis of AD, T2DM, and MDD. These shared pathways might provide novel ideas for further mechanistic studies and hub genes that may serve as novel therapeutic targets for diagnosing and treating.

Cell Cycle Regulation of Hippocampal Progenitor Cells in Experimental Models of Depression and after Treatment with Fluoxetine

Changes in adult hippocampal cell proliferation and genesis have been largely implicated in depression and antidepressant action, though surprisingly, the underlying cell cycle mechanisms are largely undisclosed. Using both an in vivo unpredictable chronic mild stress (uCMS) rat model of depression and in vitro rat hippocampal-derived neurosphere culture approaches, we aimed to unravel the cell cycle mechanisms regulating hippocampal cell proliferation and genesis in depression and after antidepressant treatment. We show that the hippocampal dentate gyrus (hDG) of uCMS animals have less proliferating cells and a decreased proportion of cells in the G2/M phase, suggesting a G1 phase arrest; this is accompanied by decreased levels of cyclin D1, E, and A expression. Chronic fluoxetine treatment reversed the G1 phase arrest and promoted an up-regulation of cyclin E. In vitro, dexamethasone (DEX) decreased cell proliferation, whereas the administration of serotonin (5-HT) reversed it. DEX also induced a G1-phase arrest and decreased cyclin D1 and D2 expression levels while increasing p27. Additionally, 5-HT treatment could partly reverse the G1-phase arrest and restored cyclin D1 expression. We suggest that the anti-proliferative actions of chronic stress in the hDG result from a glucocorticoid-mediated G1-phase arrest in the progenitor cells that is partly mediated by decreased cyclin D1 expression which may be overcome by antidepressant treatment.

The protective effects of Ghrelin/GHSR on hippocampal neurogenesis in CUMS mice

Ghrelin is an orexigenic hormone that also plays an important role in mood disorders. Our previous studies demonstrated that ghrelin administration could protect against depression-like behaviors of chronic unpredictable mild stress (CUMS) in rodents. However, the mechanism related to the effect of ghrelin on CUMS mice has yet to be revealed. This article shows that ghrelin (5 nmol/kg/day for 2 weeks, i.p.) decreased depression-like behaviors induced by CUMS and increased hippocampal integrity (neurogenesis and spine density) measured via Ki67, 5-bromo-2-deoxyuridine (BrdU), doublecortin (DCX) labeling and Golgi-cox staining, which were decreased under CUMS. The behavioral phenotypes of Growth hormone secretagogue receptor (Ghsr)-null and wild type (WT) mice were evaluated under no stress condition and after CUMS exposure to determine the effect of Ghsr knockout on the behavioral phenotypes and stress susceptibility of mice. Ghsr-null mice exhibited depression-like behaviors under no stress condition. CUMS induced similar depression- and anxiety-like behavioral manifestations in both Ghsr-null and WT mice. A similar pattern of behavioral changes was observed after hippocampal GHSR knockdown. Additionally, both Ghsr knockout as well as CUMS exhibited deleterious effects on neurogenesis and spine density in the dentate gyrus (DG). Besides, CCK8 assay and 5-Ethynyl-2'-deoxyuridine (EdU) incorporation assay showed that ghrelin has a proliferative effect on primary cultured hippocampal neural stem cells (NSCs) and this proliferation was blocked by D-Lys3-GHRP-6 (DLS, the antagonist of GHSR, 100 μM) pretreatment. Ghrelin-induced proliferation is associated with the inhibition of G1 arrest, and this inhibition was blocked by LY294002 (specific inhibitor of PI3K, 20 μM). Furthermore, the in vivo data displayed that LY294002 (50 nmol, i.c.v.) can significantly block the antidepressant-like action of exogenous ghrelin treatment. All these results suggest that ghrelin/GHSR signaling maintains the integrity of hippocampus and has an inherent neuroprotective effect whether facing stress or not.

Developmental pathway genes and neural plasticity underlying emotional learning and stress-related disorders

The manipulation of neural plasticity as a means of intervening in the onset and progression of stress-related disorders retains its appeal for many researchers, despite our limited success in translating such interventions from the laboratory to the clinic. Given the challenges of identifying individual genetic variants that confer increased risk for illnesses like depression and post-traumatic stress disorder, some have turned their attention instead to focusing on so-called "master regulators" of plasticity that may provide a means of controlling these potentially impaired processes in psychiatric illnesses. The mammalian homolog of Tailless (TLX), Wnt, and the homeoprotein Otx2 have all been proposed to constitute master regulators of different forms of plasticity which have, in turn, each been implicated in learning and stress-related disorders. In the present review, we provide an overview of the changing distribution of these genes and their roles both during development and in the adult brain. We further discuss how their distinct expression profiles provide clues as to their function, and may inform their suitability as candidate drug targets in the treatment of psychiatric disorders.

Effects of Antidepressants on DSP4/CPT-Induced DNA Damage Response in Neuroblastoma SH-SY5Y Cells

DNA damage is a form of cell stress and injury. Increased systemic DNA damage is related to the pathogenic development of neurodegenerative diseases. Depression occurs in a relatively high percentage of patients suffering from degenerative diseases, for whom antidepressants are often used to relieve depressive symptoms. However, few studies have attempted to elucidate why different groups of antidepressants have similar effects on relieving symptoms of depression. Previously, we demonstrated that neurotoxins N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4)- and camptothecin (CPT) induced the DNA damage response in SH-SY5Y cells, and DSP4 caused cell cycle arrest which was predominately in the S-phase. The present study shows that CPT treatment also resulted in similar cell cycle arrest. Some classic antidepressants could reduce the DNA damage response induced by DSP4 or CPT in SH-SY5Y cells. Cell viability examination demonstrated that both DSP4 and CPT caused cell death, which was prevented by spontaneous administration of some tested antidepressants. Flow cytometric analysis demonstrated that a majority of the tested antidepressants protect cells from being arrested in S-phase. These results suggest that blocking the DNA damage response may be an important pharmacologic characteristic of antidepressants. Exploring the underlying mechanisms may allow for advances in the effort to improve therapeutic strategies for depression appearing in degenerative and psychiatric diseases.

Re-cycling paradigms: cell cycle regulation in adult hippocampal neurogenesis and implications for depression

Since adult neurogenesis became a widely accepted phenomenon, much effort has been put in trying to understand the mechanisms involved in its regulation. In addition, the pathophysiology of several neuropsychiatric disorders, such as depression, has been associated with imbalances in adult hippocampal neurogenesis. These imbalances may ultimately reflect alterations at the cell cycle level, as a common mechanism through which intrinsic and extrinsic stimuli interact with the neurogenic niche properties. Thus, the comprehension of these regulatory mechanisms has become of major importance to disclose novel therapeutic targets. In this review, we first present a comprehensive view on the cell cycle components and mechanisms that were identified in the context of the homeostatic adult hippocampal neurogenic niche. Then, we focus on recent work regarding the cell cycle changes and signaling pathways that are responsible for the neurogenesis imbalances observed in neuropathological conditions, with a particular emphasis on depression.

Cyclin-dependent kinase 4 signaling acts as a molecular switch between syngenic differentiation and neural transdifferentiation in human mesenchymal stem cells

Multipotent mesenchymal stem/stromal cells (MSCs) are capable of differentiating into a variety of cell types from different germ layers. However, the molecular and biochemical mechanisms underlying the transdifferentiation of MSCs into specific cell types still need to be elucidated. In this study, we unexpectedly found that treatment of human adipose- and bone marrow-derived MSCs with cyclin-dependent kinase (CDK) inhibitor, in particular CDK4 inhibitor, selectively led to transdifferentiation into neural cells with a high frequency. Specifically, targeted inhibition of CDK4 expression using recombinant adenovial shRNA induced the neural transdifferentiation of human MSCs. However, the inhibition of CDK4 activity attenuated the syngenic differentiation of human adipose-derived MSCs. Importantly, the forced regulation of CDK4 activity showed reciprocal reversibility between neural differentiation and dedifferentiation of human MSCs. Together, these results provide novel molecular evidence underlying the neural transdifferentiation of human MSCs; in addition, CDK4 signaling appears to act as a molecular switch from syngenic differentiation to neural transdifferentiation of human MSCs.

Cell cycle inhibition without disruption of neurogenesis is a strategy for treatment of aberrant cell cycle diseases: an update

Since publishing our earlier report describing a strategy for the treatment of central nervous system (CNS) diseases by inhibiting the cell cycle and without disrupting neurogenesis (Liu et al. 2010), we now update and extend this strategy to applications in the treatment of cancers as well. Here, we put forth the concept of "aberrant cell cycle diseases" to include both cancer and CNS diseases, the two unrelated disease types on the surface, by focusing on a common mechanism in each aberrant cell cycle reentry. In this paper, we also summarize the pharmacological approaches that interfere with classical cell cycle molecules and mitogenic pathways to block the cell cycle of tumor cells (in treatment of cancer) as well as to block the cell cycle of neurons (in treatment of CNS diseases). Since cell cycle inhibition can also block proliferation of neural progenitor cells (NPCs) and thus impair brain neurogenesis leading to cognitive deficits, we propose that future strategies aimed at cell cycle inhibition in treatment of aberrant cell cycle diseases (i.e., cancers or CNS diseases) should be designed with consideration of the important side effects on normal neurogenesis and cognition.

nNOS deficiency-induced cell proliferation depletes the neurogenic reserve

The consequences of nitric oxide synthase (NOS) gene knockout on proliferation, survival and differentiation of neuronal precursors in the subgranular (SGZ) and subventricular (SVZ) zones were analyzed. Comparative studies were performed in neonatal, adult and old (18-month) wild-type (WT), nNOS, eNOS, and iNOS knockout (KO) mice. Effects on brain cell proliferation were studied by sacrificing animals at 24h after injecting BrdU, while effects on survival and differentiation of dividing brain cells were studied by sacrificing other animals at three weeks after injections and double immunostaining with cell phenotype-specific antibodies. In the neonatal SGZ, cell proliferation was higher than at any other age, with a significantly decreased level in eNOS-KO mice. In the neonatal SVZ, cell proliferation in each of the three NOS-KO strains was significantly lower than in WT. In the adult, in both the SGZ and SVZ, all strains showed lower levels of cell proliferation than in neonates. Thereby, the significant highest cell proliferation was found in the SGZ and SVZ of nNOS-KO mice. In the SGZ and SVZ of old mice, in each strain, BrdU-positive cell counts were further reduced from adult levels, whereby cell proliferation of nNOS-KO mice attained the most massive reduction (in the SGZ almost to zero). In adult animals sacrificed 21 days after BrdU injections, values of BrdU-/NeuN-positive cells in all knockout animals were the same as WT, indicating that the initial cell proliferation changes were not sustained or translated into neuronal differentiation. The effect of nNOS-KO, inducing cell proliferation only temporarily, consists with the concept that neuronal stem cells have a finite proliferation capacity.

Antidepressants increase human hippocampal neurogenesis by activating the glucocorticoid receptor

Antidepressants increase adult hippocampal neurogenesis in animal models, but the underlying molecular mechanisms are unknown. In this study, we used human hippocampal progenitor cells to investigate the molecular pathways involved in the antidepressant-induced modulation of neurogenesis. Because our previous studies have shown that antidepressants regulate glucocorticoid receptor (GR) function, we specifically tested whether the GR may be involved in the effects of these drugs on neurogenesis. We found that treatment (for 3-10 days) with the antidepressant, sertraline, increased neuronal differentiation via a GR-dependent mechanism. Specifically, sertraline increased both immature, doublecortin (Dcx)-positive neuroblasts (+16%) and mature, microtubulin-associated protein-2 (MAP2)-positive neurons (+26%). This effect was abolished by the GR-antagonist, RU486. Interestingly, progenitor cell proliferation, as investigated by 5'-bromodeoxyuridine (BrdU) incorporation, was only increased when cells were co-treated with sertraline and the GR-agonist, dexamethasone, (+14%) an effect which was also abolished by RU486. Furthermore, the phosphodiesterase type 4 (PDE4)-inhibitor, rolipram, enhanced the effects of sertraline, whereas the protein kinase A (PKA)-inhibitor, H89, suppressed the effects of sertraline. Indeed, sertraline increased GR transactivation, modified GR phosphorylation and increased expression of the GR-regulated cyclin-dependent kinase-2 (CDK2) inhibitors, p27(Kip1) and p57(Kip2). In conclusion, our data suggest that the antidepressant, sertraline, increases human hippocampal neurogenesis via a GR-dependent mechanism that requires PKA signaling, GR phosphorylation and activation of a specific set of genes. Our data point toward an important role for the GR in the antidepressant-induced modulation of neurogenesis in humans.

Cell cycle inhibition without disruption of neurogenesis is a strategy for treatment of central nervous system diseases

Classically, the cell cycle is regarded as the process leading to cellular proliferation. However, increasing evidence over the last decade supports the notion that neuronal cell cycle re-entry results in post-mitotic death. A mature neuron that re-enters the cell cycle can neither advance to a new G0 quiescent state nor revert to its earlier G0 state. This presents a critical dilemma to the neuron from which death may be an unavoidable but necessary outcome for adult neurons attempting to complete the cell cycle. In contrast, tumor cells that undergo aberrant cell cycle re-entry divide and can survive. Thus, cell cycle inhibition strategies are of interest in cancer treatment but may also represent an important means of protecting neurons. In this review, we put forth the concept of the "expanded cell cycle" and summarize the cell cycle proteins, signal transduction events and mitogenic molecules that can drive a neuron into the cell cycle in various CNS diseases. We also discuss the pharmacological approaches that interfere with the mitogenic pathways and prevent mature neurons from attempting cell cycle re-entry, protecting them from cell death. Lastly, future attempts at blocking the cell cycle to rescue mature neurons from injury should be designed so as to not block normal neurogenesis.