Proliferation of hippocampal progenitors relies on p27-dependent regulation of Cdk6 kinase activity

Cyclin-dependent kinase inhibitor p18 regulates lineage transitions of excitatory neurons, astrocytes, and interneurons in the mouse cortex

Neural stem cells (NSCs) can give rise to both neurons and glia, but the regulatory mechanisms governing their differentiation transitions remain incompletely understood. Here, we address the role of cyclin-dependent kinase inhibitors (CDKIs) in the later stages of dorsal cortical development. We find that the CDKIs p18 and p27 are upregulated at the onset of astrocyte generation. Acute manipulation of p18 and p27 levels shows that CDKIs modulate lineage switching between upper-layer neurons and astrocytes at the transitional stage. We generate a conditional knock-in mouse model to induce p18 in NSCs. The transcriptomic deconvolution of microdissected tissue reveals that increased levels of p18 promote glial cell development and activate Delta-Notch signaling. Furthermore, we show that p18 upregulates the homeobox transcription factor Dlx2 to subsequently induce the differentiation of olfactory bulb interneurons while reducing the numbers of upper-layer neurons and astrocytes at the perinatal stage. Clonal analysis using transposon-based reporters reveals that the transition from the astrocyte to the interneuron lineage is potentiated by p18 at the single-cell level. In sum, our study reports a function of p18 in determining the developmental boundaries among different cellular lineages arising sequentially from NSCs in the dorsal cortex.

N-Myc transcriptionally activates Skp2 to suppress p27 expression in small cell lung cancer

BACKGROUND

Small cell lung cancer (SCLC) is characterized by a high proliferative rate, a strong predilection for early metastasis and poor prognosis. Novel SCLC biomarkers are urgently required to improve current diagnostic and treatment modalities. MYCN encodes the proto-oncogene N-Myc that is overexpressed in SCLC, but its downstream effectors are poorly characterized. Here, we investigated the role of the N-Myc/Skp2/p27 axis during SCLC progression.

METHODS

Immunohistochemistry (IHC) and western blotting were performed to evaluate N-Myc/Skp2/p27 expression. SCLC cell apoptosis was investigated through TUNEL staining. Wound healing and transwell assays were performed to detect the migratory and invasive potential of SCLC cells. N-Myc and Skp2 binding was confirmed through luciferase reporter and ChIP assays. Xenograft models were developed to investigate the function of Skp2 during SCLC tumor growth in vivo.

RESULTS

N-Myc and Skp2 were overexpressed in SCLC, whilst p27 expression was suppressed. Skp2 facilitated SCLC progression by protecting cells from apoptosis and facilitating cell migration and invasion. N-Myc was found to bind to the promoter region of Skp2 to enhance its expression. Skp2 enhanced tumor growth in vivo through the suppression of p27. Skp2 silencing reversed the pro-oncogenic effects of N-myc in SCLC tumors.

CONCLUSION

We show that N-Myc enhances Skp2 to regulate p27 expression during SCLC progression. We therefore highlight the N-Myc/Skp2/p27 axis as a novel diagnostic and much-needed therapeutic target in SCLC.

MiRNA-494-3p Regulates Bupivacaine-Induced Neurotoxicity by the CDK6-PI3K/AKT Signaling

Bupivacaine (BUP) is a long-acting amide local anesthetic that may induce strong neurotoxicity and neurological complications. In this study, we elucidate the influence of microRNA-494-3p (miR-494-3p) in BUP-induced neurotoxicity in primary mouse hippocampal neuronal cells. In this study, primary hippocampal neurons were isolated from neonatal C57BL/6 mice. The isolated neurons were treated with various doses of BUP. MTT assay was conducted to analyze neuronal viability. Gene expression measurement was done by RT-qPCR. The impact of miR-494-3p in BUP-mediated neural injury was examined using TUNEL, flow cytometry, western blotting, and ROS activity detection. The regulatory relationship between miR-494-3p and cyclin-dependent kinases 4 and 6 (CDK6) was identified using a luciferase reporter assay. BUP treatment led to neurotoxicity and miR-494-3p upregulation in primary cultured hippocampal neurons. Functionally, miR-494-3p depletion alleviated neuronal apoptosis and oxidative damage induced by BUP. We verified that miR-494-3p targeted and negatively modulated CDK6. MiR-494-3p depletion also activated PI3K/AKT signaling by elevating CDK6 expression in BUP-treated neurons. Furthermore, CDK6 knockdown or PI3K/AKT inactivation attenuated the neuroprotective role of miR-494-3p depletion. Silencing miR-494-3p exerts neuroprotective function in hippocampal neuronal cells against BUP-induced injury by the CDK6-PI3K/AKT pathway.

Function of Oncogene Mycn in Adult Neurogenesis and Oligodendrogenesis

Human MYCN is an oncogene amplified in neuroblastoma and many other tumors. Both human MYCN and mouse Mycn genes are important in embryonic brain development, but their functions in adult healthy nerve system are completely unknown. Here, with Mycn-eGFP mice and quantitative RT-PCR, we found that Mycn was expressed in specific brain regions of young adult mice, including subventricular zone (SVZ), subgranular zone (SGZ), olfactory bulb (OB), subcallosal zone (SCZ), and corpus callosum (CC). With immunohistochemistry (IHC), we found that many Mycn-expressing cells expressed neuroblast marker doublecortin (DCX) and proliferation marker Ki67. With Dcx-creER and Mki67-creER mouse lines, we fate mapped Dcx-expressing neuroblasts and Mki67-expressing proliferation cells, along with deleting Mycn from these cells in adult mice. We found that knocking out Mycn from adult neuroblasts or proliferating cells significantly reduced cells in proliferation in SVZ, SGZ, OB, SCZ, and CC. We also demonstrated that the Mycn-deficient neuroblasts in SGZ matured quicker than wild-type neuroblasts, and that Mycn-deficient proliferating cells were more likely to survive in SVZ, SGZ, OB, SCZ, and CC compared to wild type. Thus, our results demonstrate that, in addition to causing tumors in the nervous system, oncogene Mycn has a crucial function in neurogenesis and oligodendrogenesis in adult healthy brain.

The Yin and Yang of Autosomal Recessive Primary Microcephaly Genes: Insights from Neurogenesis and Carcinogenesis

The stem cells of neurogenesis and carcinogenesis share many properties, including proliferative rate, an extensive replicative potential, the potential to generate different cell types of a given tissue, and an ability to independently migrate to a damaged area. This is also evidenced by the common molecular principles regulating key processes associated with cell division and apoptosis. Autosomal recessive primary microcephaly (MCPH) is a neurogenic mitotic disorder that is characterized by decreased brain size and mental retardation. Until now, a total of 25 genes have been identified that are known to be associated with MCPH. The inactivation (yin) of most MCPH genes leads to neurogenesis defects, while the upregulation (yang) of some MCPH genes is associated with different kinds of carcinogenesis. Here, we try to summarize the roles of MCPH genes in these two diseases and explore the underlying mechanisms, which will help us to explore new, attractive approaches to targeting tumor cells that are resistant to the current therapies.

iTRAQ-based quantitative proteomic analysis provides insight for molecular mechanism of neuroticism

Background

Neuroticism is a core personality trait and a major risk factor for several mental and physical diseases, particularly in females, who score higher on neuroticism than men, on average. However, a better understanding of the expression profiles of proteins in the circulating blood of different neurotic female populations may help elucidate the intrinsic mechanism of neurotic personality and aid prevention strategies on mental and physical diseases associated with neuroticism.

Methods

In our study, female subjects were screened for inclusion by the Eysenck Personality Questionnaire (EPQ), Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI) scales and routine physical examination. Subjects who passed the examination and volunteered to participate were grouped by neuroticism using EPQ scores (0 and 1 = low neuroticism group; > 5 = high neuroticism group). Proteins in serum samples of the two neuroticism groups were identified using isobaric tags for relative and absolute quantification (iTRAQ) technology.

Results

A total of 410 proteins exhibited significant differences between high and low neuroticism, 236 proteins were significantly upregulated and 174 proteins were significantly downregulated. Combine the results of GO and KEGG enrichment analysis of differences proteins between high and low neuroticism with the PPI network, it could be observed that the Alpha-synuclein (SNCA), ATP7A protein (ATP7A), Guanine nucleotide-binding protein G(I)/G(S)/G(O) subunit gamma-2 (GNG2), cyclin-dependent kinase 6 (CDK6), myeloperoxidase (MPO), azurocidin (AZU1), Histone H2B type 1-H (HIST1H2BH), Integrin alpha-M (ITGAM) and Matrix metalloproteinase-9 (MMP9) might participate in the intrinsic mechanism of neuroticism by regulating response to catecholamine stimulus, catecholamine metabolic process, limbic system development and transcriptional misregulation in cancer pathway.

Conclusions

Our study revealed the characteristics of the neurotic personality proteome, which might be intrinsic mechanism of the neurotic population.

Growth Arrest Triggers Extra-Cell Cycle Regulatory Function in Neurons: Possible Involvement of p27kip1 in Membrane Trafficking as Well as Cytoskeletal Regulation

Cell cycle regulation is essential for the development of multicellular organisms, but many cells in adulthood, including neurons, exit from cell cycle. Although cell cycle-related proteins are suppressed after cell cycle exit in general, recent studies have revealed that growth arrest triggers extra-cell cycle regulatory function (EXCERF) in some cell cycle proteins, such as p27(kip1), p57(kip2), anaphase-promoting complex/cyclosome (APC/C), and cyclin E. While p27 is known to control G1 length and cell cycle exit via inhibition of cyclin-dependent kinase (CDK) activities, p27 acquires additional cytoplasmic functions in growth-arrested neurons. Here, we introduce the EXCERFs of p27 in post-mitotic neurons, mainly focusing on its actin and microtubule regulatory functions. We also show that a small amount of p27 is associated with the Golgi apparatus positive for Rab6, p115, and GM130, but not endosomes positive for Rab5, Rab7, Rab8, Rab11, SNX6, or LAMTOR1. p27 is also colocalized with Dcx, a microtubule-associated protein. Based on these results, we discuss here the possible role of p27 in membrane trafficking and microtubule-dependent transport in post-mitotic cortical neurons. Collectively, we propose that growth arrest leads to two different fates in cell cycle proteins; either suppressing their expression or activating their EXCERFs. The latter group of proteins, including p27, play various roles in neuronal migration, morphological changes and axonal transport, whereas the re-activation of the former group of proteins in post-mitotic neurons primes for cell death.

Divide or Commit - Revisiting the Role of Cell Cycle Regulators in Adult Hippocampal Neurogenesis

The adult dentate gyrus continuously generates new neurons that endow the brain with increased plasticity, helping to cope with changing environmental and cognitive demands. The process leading to the birth of new neurons spans several precursor stages and is the result of a coordinated series of fate decisions, which are tightly controlled by extrinsic signals. Many of these signals act through modulation of cell cycle (CC) components, not only to drive proliferation, but also for linage commitment and differentiation. In this review, we provide a comprehensive overview on key CC components and regulators, with emphasis on G₁ phase, and analyze their specific functions in precursor cells of the adult hippocampus. We explore their role for balancing quiescence versus self-renewal, which is essential to maintain a lifelong pool of neural stem cells while producing new neurons “on demand.” Finally, we discuss available evidence and controversies on the impact of CC/G₁ length on proliferation versus differentiation decisions.

Silencing of lncRNA PKIA-AS1 Attenuates Spinal Nerve Ligation-Induced Neuropathic Pain Through Epigenetic Downregulation of CDK6 Expression

Neuropathic pain (NP) is among the most intractable comorbidities of spinal cord injury. Dysregulation of non-coding RNAs has also been implicated in the development of neuropathic pain. Here, we identified a novel lncRNA, PKIA-AS1, by using lncRNA array analysis in spinal cord tissue of spinal nerve ligation (SNL) model rats, and investigated the role of PKIA-AS1 in SNL-mediated neuropathic pain. We observed that PKIA-AS1 was significantly upregulated in SNL model rats and that PKIA-AS1 knockdown attenuated neuropathic pain progression. Alternatively, overexpression of PKIA-AS1 was sufficient to induce neuropathic pain-like symptoms in uninjured rats. We also found that PKIA-AS1 mediated SNL-induced neuropathic pain by directly regulating the expression and function of CDK6, which is essential for the initiation and maintenance of neuroinflammation and neuropathic pain. Therefore, our study identifies PKIA-AS1 as a novel therapeutic target for neuroinflammation related neuropathic pain.