Endoplasmic reticulum stress prolongs GH-induced Janus kinase (JAK2)/signal transducer and activator of transcription (STAT5) signaling pathway

ALKBH5 protects against stroke by reducing endoplasmic reticulum stress-dependent inflammation injury via the STAT5/PERK/EIF2α/CHOP signaling pathway in an m6A-YTHDF1-dependent manner

BACKGROUND

Endoplasmic reticulum (ER) stress causes neuroinflammation and neuronal apoptosis during ischemic stroke progression. This study has investigated the role of ALKBH5 in ER stress during ischemic stroke progression.

METHODS

In vivo and in vitro models of ischemic stroke were established by middle cerebral artery occlusion (MCAO) and OGD/R treatment, respectively. Cerebral infarct size was detected using triphenyltetrazolium chloride staining (TTC), and pathological changes were examined using histological staining. The levels of inflammatory factors were analyzed using Enzyme-linked immunosorbent assay. Cell counting kit-8 assay and flow cytometry were used to measure cell viability and apoptosis, respectively. The global m6A level was detected using the commercial kit, and STAT5 mRNA m6A level was determined using methylated RNA binding protein immunoprecipitation (Me-RIP). ALKBH5, YTHDF1, and STAT5 interactions were analyzed using RIP and RNA pull-down assays.

RESULTS

ALKBH5 was upregulated in MCAO animals and OGD/R cell models. ALKBH5 knockdown exacerbated ER stress, neuroinflammation, and neuronal apoptosis in brain tissues and neuronal cells. ALKBH5 inhibited STAT5 mRNA stability and expression in an m6A-YTHDF1-dependent manner. STAT5 promoted ER stress by activating the PERK/eIF2/CHOP signaling pathway. Furthermore, STAT5 knockdown reversed the effects of ALKBH5 knockdown on OGD/R-induced ER stress and neuroinflammation in HT22 cells.

CONCLUSION

ALKBH5 knockdown exacerbated ischemic stroke by increasing ER stress-dependent neuroinflammation and neuronal apoptosis via the STAT5/PERK/EIF2α/CHOP signaling pathway in an m6A-YTHDF1-dependent manner.

Modulating Stress Proteins in Response to Therapeutic Interventions for Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative illness characterized by the degeneration of dopaminergic neurons in the substantia nigra, resulting in motor symptoms and without debilitating motors. A hallmark of this condition is the accumulation of misfolded proteins, a phenomenon that drives disease progression. In this regard, heat shock proteins (HSPs) play a central role in the cellular response to stress, shielding cells from damage induced by protein aggregates and oxidative stress. As a result, researchers have become increasingly interested in modulating these proteins through pharmacological and non-pharmacological therapeutic interventions. This review aims to provide an overview of the preclinical experiments performed over the last decade in this research field. Specifically, it focuses on preclinical studies that center on the modulation of stress proteins for the treatment potential of PD. The findings display promise in targeting HSPs to ameliorate PD outcomes. Despite the complexity of HSPs and their co-chaperones, proteins such as HSP70, HSP27, HSP90, and glucose-regulated protein-78 (GRP78) may be efficacious in slowing or preventing disease progression. Nevertheless, clinical validation is essential to confirm the safety and effectiveness of these preclinical approaches.

Erythropoietin Nanobots: Their Feasibility for the Controlled Release of Erythropoietin and Their Neuroprotective Bioequivalence in Central Nervous System Injury

Background: Erythropoietin (EPO) plays important roles in neuroprotection in central nervous system injury. Due to the limited therapeutic time window and coexistence of hematopoietic/extrahematopoietic receptors displaying heterogenic and phylogenetic differences, fast, targeted delivery agents, such as nanobots, are needed. To confirm the feasibility of EPO-nanobots (ENBs) as therapeutic tools, the authors evaluated controlled EPO release from ENBs and compared the neuroprotective bioequivalence of these substances after preconditioning sonication. Methods: ENBs were manufactured by a nanospray drying technique with preconditioning sonication. SH-SY5Y neuronal cells were cotreated with thapsigargin and either EPO or ENBs before cell viability, EPO receptor activation, and endoplasmic reticulum stress-related pathway deactivation were determined over 24 h. Results: Preconditioning sonication (50–60 kHz) for 1 h increased the cumulative EPO release from the ENBs (84% versus 25% at 24 h). Between EPO and ENBs at 24 h, both neuronal cell viability (both > 65% versus 15% for thapsigargin alone) and the expression of the proapoptotic/apoptotic biomolecular markers JAK2, PDI, PERK, GRP78, ATF6, CHOP, TGF-β, and caspase-3 were nearly the same or similar. Conclusion: ENBs controlled EPO release in vitro after preconditioning sonication, leading to neuroprotection similar to that of EPO at 24 h.

RIG-I promotes IFN/JAK2 expression and the endoplasmic reticulum stress response to inhibit chemoradiation resistance in nasopharyngeal carcinoma

RIG-I is associated with the occurrence and development of many tumors. However, the role of RIG-I in radiotherapy and chemotherapy in NPC has not been reported to date. In our study, RIG-I expression was significantly reduced in chemoradiotherapy-resistant NPC tissues and cells compared with that in therapy-sensitive tissues and cells. RIG-I expression increased in nonresistant NPC cells, including CNE1 and CNE2, in a dose-dependent manner with increasing chemotherapy drug concentration or radiotherapy dose. RIG-I overexpression promoted radiotherapy and chemotherapy sensitivity in NPC cells, leading to cellular apoptosis and increased expression of the proapoptotic factors BAX and caspase-3. Similarly, RIG-I knockdown in NPC cells promoted chemoradiotherapy resistance and reduced apoptosis. Analysis of microarray data indicated that the expression of IFN/JAK2 and endoplasmic reticulum (ER) stress response markers, such as JAK2, STAT1, IRF9, IFNB1, IRF3, p-IRF3, XBP1, ATF6, IFIT2, and ISG15, was inhibited in chemoradiotherapy-resistant cells compared with that in sensitive cells. Conversely, activation of IFN/JAK2 and ER stress response pathways in NPC cells reduced paclitaxel resistance and increased apoptosis. RIG-I promotes IFN/JAK2 and ER stress response-mediated apoptosis to inhibit chemoradiation resistance in nasopharyngeal carcinoma.

Cyadox regulates the transcription of different genes by activation of the PI3K signaling pathway in porcine primary hepatocytes

Cyadox, a new derivative of quinoxalines, has been ascertained as an antibiotic with significant growth promoting, low poison, quick absorption, swift elimination, brief residual period, and noncumulative effect. Seven differential expressed genes, including Insulin-like Growth Factor-1 ( IGF-1), Epidermal Growth Factor ( EGF), Poly ADP-ribose polymerase ( PARP), the Defender Against Apoptotic Death 1 ( DAD1), Complement Component 3 ( C3), Transketolase ( TK) and a New gene, were induced by cyadox in swine liver tissues by messenger RNA differential display reverse transcription polymerase chain reaction (DDRT-PCR) in our laboratory. However, the signal mechanism that cyadox altered these genes expression is not completely elucidated. The signaling pathways involved in the expressions of seven genes induced by cyadox were determined in porcine primary hepatocytes by RT-qPCR and the application of various signal pathway inhibitors. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay revealed that cyadox could stimulate proliferation of porcine primary hepatocytes in a time-dependent manner. In porcine primary cultured hepatocytes, phosphoinositide 3-kinase (PI3K) and transforming growth factor-β (TGF-β) signal pathways were the main signal pathways involved in the expressions of seven genes induced by cyadox. Taken together, these results demonstrate for the first time that seven cyadox-related genes expressions in porcine primary hepatocytes treated with cyadox are mediated mainly through the PI3K signaling pathway, potentially leading to enhanced cell growth and cell immunity. EGF might be the early response gene of cyadox, and a primary regulator of the other gene expressions such as IGF-1 and DAD1, playing an important role in cell proliferation promoted by cyadox.

Endoplasmic reticulum stress and inflammation in the central nervous system

Persistent endoplasmic reticulum (ER) stress is thought to drive the pathology of many chronic disorders due to its potential to elicit aberrant inflammatory signaling and facilitate cell death. In neurodegenerative diseases, the accumulation of misfolded proteins and concomitant induction of ER stress in neurons contributes to neuronal dysfunction. In addition, ER stress responses induced in the surrounding neuroglia may promote disease progression by coordinating damaging inflammatory responses, which help fuel a neurotoxic milieu. Nevertheless, there still remains a gap in knowledge regarding the cell-specific mechanisms by which ER stress mediates neuroinflammation. In this review, we will discuss recently uncovered inflammatory pathways linked to the ER stress response. Moreover, we will summarize the present literature delineating how ER stress is generated in Alzheimer’s disease, Parkinson’s disease, Amyotrophic Lateral Sclerosis, and Multiple Sclerosis, and highlight how ER stress and neuroinflammation intersect mechanistically within the central nervous system. The mechanisms by which stress-induced inflammation contributes to the pathogenesis and progression of neurodegenerative diseases remain poorly understood. Further examination of this interplay could present unappreciated insights into the development of neurodegenerative diseases, and reveal new therapeutic targets.

PERK-dependent activation of JAK1 and STAT3 contributes to endoplasmic reticulum stress-induced inflammation

Neuroinflammation and endoplasmic reticulum (ER) stress are associated with many neurological diseases. Here, we have examined the interaction between ER stress and JAK/STAT-dependent inflammation in glial cells. We show that ER stress is present in the central nervous system (CNS) concomitant with inflammation and astrogliosis in the multiple sclerosis (MS) mouse model of experimental autoimmune encephalomyelitis (EAE). Astrocytes do not easily succumb to ER stress but rather activate an inflammatory program involving activation of STAT3 in a JAK1-dependent fashion. ER stress-induced activation of the JAK1/STAT3 axis leads to expression of interleukin 6 (IL-6) and several chemokines. Moreover, the activation of STAT3 signaling is dependent on PERK, a central component of the ER stress response, which we show is phosphorylated by JAK1. Disruption of PERK abrogates ER stress-induced activation of STAT3 and subsequent gene expression. Additionally, ER-stressed astrocytes, via paracrine signaling, can stimulate activation of microglia, leading to production of IL-6 and oncostatin M (OSM). These IL-6 cytokines can then synergize with ER stress in astrocytes to drive inflammation. Together, this work describes a new PERK/JAK1/STAT3 signaling pathway that elicits a feed-forward inflammatory loop involving astrocytes and microglia to drive neuroinflammation, which may be relevant in diseases such as MS.

Bortezomib inhibits STAT5-dependent degradation of LEF-1, inducing granulocytic differentiation in congenital neutropenia CD34(+) cells

The transcription factor lymphoid enhancer-binding factor 1 (LEF-1), which plays a definitive role in granulocyte colony-stimulating factor (G-CSF) receptor-triggered granulopoiesis, is downregulated in granulocytic progenitors of severe congenital neutropenia (CN) patients. However, the exact mechanism of LEF-1 downregulation is unclear. CN patients are responsive to therapeutically high doses of G-CSF and are at increased risk of developing acute myeloid leukemia. The normal expression of LEF-1 in monocytes and lymphocytes, whose differentiation is unaffected in CN, suggests the presence of a granulopoiesis-specific mechanism downstream of G-CSF receptor signaling that leads to LEF-1 downregulation. Signal transducer and activator of transcription 5 (STAT5) is activated by G-CSF and is hyperactivated in acute myeloid leukemia. Here, we investigated the effects of activated STAT5 on LEF-1 expression and functions in hematopoietic progenitor cells. We demonstrated that constitutively active STAT5a (caSTAT5a) inhibited LEF-1-dependent autoregulation of the LEF-1 gene promoter by binding to the LEF-1 protein, recruiting Nemo-like kinase and the E3 ubiquitin-ligase NARF to LEF-1, leading to LEF-1 ubiquitination and a reduction in LEF-1 protein levels. The proteasome inhibitor bortezomib reversed the defective G-CSF-triggered granulocytic differentiation of CD34(+) cells from CN patients in vitro, an effect that was accompanied by restoration of LEF-1 protein levels and LEF-1 messenger RNA autoregulation. Taken together, our data define a novel mechanism of LEF-1 downregulation in CN patients via enhanced ubiquitination and degradation of LEF-1 protein by hyperactivated STAT5.

Transcriptional regulation of the human growth hormone receptor (hGHR) gene V2 promoter by transcriptional activators and repressor

The V2 transcript is the major ubiquitously expressed human GH receptor (hGHR) mRNA in all tissues examined to date. In a previous investigation, we defined the V2 promoter as TATA-less and exhibiting many characteristics of a housekeeping gene promoter. We also demonstrated that its basal activity is determined by several different cis-regulatory regions within both the promoter and the V2 exon. In the present study, we used luciferase-reporter, site-directed mutagenesis, gel shift, chromatin immunoprecipitation, and quantitative RT-PCR assays to investigate the ability of certain transcription factors to regulate hGHR V2 transcription through these regions in mammalian cells, including human adipocytes. Ets1 was found to transactivate the V2 proximal promoter through specific Ets sites. Two CCAAT/enhancer-binding protein (C/EBP) family members [C/EBP-homologous protein (CHOP) and C/EBPbeta] enhanced V2 transcription via different pathways: indirectly, by association with a V2 exon region (CHOP), and directly, using a V2 proximal promoter noncanonical binding site (C/EBPbeta). The Notch signaling mediator, Hes1, potently suppressed V2 promoter activity through interaction with two Hes sites within the V2 exon. We propose that these transcriptional factors regulate hGHR V2 expression by acting as downstream nuclear effectors, linking specific signaling cascades (e.g. MAPK and Notch) triggered by different growth factor-, development-, and nutrition- as well as stress-related stimuli. Our data also suggest that these factors are likely to be important in the differentiation-induced increase in V2 mRNA expression in adipocytes, with Ets1 and CHOP functioning at the preadipocyte stage to prepare the cells for differentiation and increasing C/EBPs and decreasing Hes1 levels contributing during adipocyte maturation.

In Vivo Transcript Profiling and Phylogenetic Analysis Identifies Suppressor of Cytokine Signaling 2 as a Direct Signal Transducer and Activator of Transcription 5b Target in Liver

The GH-activated signal transducer and activator of transcription 5b (STAT5b) is an essential regulator of somatic growth. The transcriptional response to STAT5b in liver is poorly understood. We have combined microarray-based expression profiling and phylogenetic analysis of gene regulatory regions to study the interplay between STAT5b and GH in the regulation of hepatic gene expression. The acute transcriptional response to GH in vivo after a single pulse of GH was studied in the liver of hypophysectomized rats in the presence of either constitutively active or a dominant-negative STAT5b delivered by adenoviral gene transfer. Genes showing differential expression in these two situations were analyzed for the presence of STAT5b binding sites in promoter and intronic regions that are phylogenetically conserved between rats and humans. Using this approach, we showed that most rapid transcriptional effects of GH in the liver are not results of direct actions of STAT5b. In addition, we identified novel STAT5b cis regulatory elements in genes such as Frizzled-4, epithelial membrane protein-1, and the suppressor of cytokine signaling 2 (SOCS2). Detailed analysis of SOCS2 promoter demonstrated its direct transcriptional regulation by STAT5b upon GH stimulation. A novel response element was identified within the first intron of the human SOCS2 gene composed of an E-box followed by tandem STAT5b binding sites, both of which are required for full GH responsiveness. In summary, we demonstrate the power of combining transcript profiling with phylogenetic sequence analysis to define novel regulatory paradigms.

Negative regulation of growth hormone receptor signaling

GH has been of significant scientific interest for decades because of its capacity to dramatically change physiological growth parameters. Furthermore, GH interacts with a range of other hormonal pathways and is an established pharmacological agent for which novel therapeutical applications can be foreseen. It is easy to see the requirement for a number of postreceptor mechanisms to regulate and control target tissue sensitivity to this versatile hormone. In recent years, some of the components that take part in the down-regulatory mechanism targeting the activated GH receptor (GHR) have been defined, and the physiological significance of some of these key components has begun to be characterized. Down-regulation of the GHR is achieved through a complex mechanism that involves rapid ubiquitin-dependent endocytosis of the receptor, the action of tyrosine phosphatases, and the degradation by the proteasome. The suppressors of cytokine signaling (SOCS) protein family, particularly SOCS2, plays an important role in regulating GH actions. The aim of this review is to summarize collected knowledge, including very recent findings, regarding the intracellular mechanisms responsible for the GHR signaling down-regulation. Insights into these mechanisms can be of relevance to several aspects of GH research. It can help to understand growth-related disease conditions, to explain GH resistance, and may be used to develop pharmaceuticals that enhance some the beneficial actions of endogenously secreted GH in a tissue-specific manner.

SOCS2 negatively regulates growth hormone action in vitro and in vivo

Mice deficient in SOCS2 display an excessive growth phenotype characterized by a 30-50% increase in mature body size. Here we show that the SOCS2-/- phenotype is dependent upon the presence of endogenous growth hormone (GH) and that treatment with exogenous GH induced excessive growth in mice lacking both endogenous GH and SOCS2. This was reflected in terms of overall body weight, body and bone lengths, and the weight of internal organs and tissues. A heightened response to GH was also measured by examining GH-responsive genes expressed in the liver after exogenous GH administration. To further understand the link between SOCS2 and the GH-signaling cascade, we investigated the nature of these interactions using structure/function and biochemical interaction studies. Analysis of the 3 structural motifs of the SOCS2 molecule revealed that each plays a crucial role in SOCS2 function, with the conserved SOCS-box motif being essential for all inhibitory function. SOCS2 was found to bind 2 phosphorylated tyrosines on the GH receptor, and mutational analysis of these amino acids showed that both were essential for SOCS2 function. Together, the data provide clear evidence that SOCS2 is a negative regulator of GH signaling.

Protein tyrosine phosphatase 1B attenuates growth hormone-mediated JAK2-STAT signaling

Protein tyrosine phosphatase-1B (PTP-1B) attenuates insulin, PDGF, EGF, and IGF-I signaling by dephosphorylating tyrosine residues located in the tyrosine kinase domain of the corresponding receptors. More recently, PTP-1B was shown to modulate the action of cytokine signaling via the nonreceptor tyrosine kinase JAK2. Transmission of the growth hormone (GH) signal also depends on JAK2, raising the possibility that PTP-1B modulates GH action. Consistent with this hypothesis, GH increased the abundance of tyrosine-phosphorylated JAK2 associated with a catalytically inactive mutant of PTP-1B. GH-induced JAK2 phosphorylation was greater in knockout (KO) than in wild-type (WT) PTP-1B embryonic fibroblasts and resulted in increased tyrosine phosphorylation of STAT3 and STAT5, while overexpression of PTP-1B reduced the GH-mediated activation of the acid-labile subunit gene. To evaluate the in vivo relevance of these observations, mice were injected with GH under fed and fasted conditions. As expected, tyrosine phosphorylation of JAK2 and STAT5 occurred readily in the livers of fed WT mice and was almost completely abolished during fasting. In contrast, resistance to the action of GH was severely impaired in the livers of fasted KO mice. These results indicate that PTP-1B regulates GH signaling by reducing the extent of JAK2 phosphorylation and suggest that PTP-1B is essential for limiting the action of GH during metabolic stress such as fasting.