Comparative Analysis of Protein Tyrosine Phosphatases Regulating Microglial Activation

A novel rhein-huprine hybrid ameliorates disease-modifying properties in preclinical mice model of Alzheimer's disease exacerbated with high fat diet

BACKGROUND

Alzheimer's disease (AD) is characterized by a polyetiological origin. Despite the global burden of AD and the advances made in AD drug research and development, the cure of the disease remains elusive, since any developed drug has demonstrated effectiveness to cure AD. Strikingly, an increasing number of studies indicate a linkage between AD and type 2 diabetes mellitus (T2DM), as both diseases share some common pathophysiological features. In fact, β-secretase (BACE1) and acetylcholinesterase (AChE), two enzymes involved in both conditions, have been considered promising targets for both pathologies. In this regard, due to the multifactorial origin of these diseases, current research efforts are focusing on the development of multi-target drugs as a very promising option to derive effective treatments for both conditions. In the present study, we evaluated the effect of rhein-huprine hybrid (RHE-HUP), a synthesized BACE1 and AChE inhibitor, both considered key factors not only in AD but also in metabolic pathologies. Thus, the aim of this study is to evaluate the effects of this compound in APP/PS1 female mice, a well-established familial AD mouse model, challenged by high-fat diet (HFD) consumption to concomitantly simulate a T2DM-like condition.

RESULTS

Intraperitoneal treatment with RHE-HUP in APP/PS1 mice for 4 weeks reduced the main hallmarks of AD, including Tau hyperphosphorylation, Aβ₄₂ peptide levels and plaque formation. Moreover, we found a decreased inflammatory response together with an increase in different synaptic proteins, such as drebrin 1 (DBN1) or synaptophysin, and in neurotrophic factors, especially in BDNF levels, correlated with a recovery in the number of dendritic spines, which resulted in memory improvement. Notably, the improvement observed in this model can be attributed directly to a protein regulation at central level, since no peripheral modification of those alterations induced by HFD consumption was observed.

CONCLUSIONS

Our results suggest that RHE-HUP could be a new candidate for the treatment of AD, even for individuals with high risk due to peripheral metabolic disturbances, given its multi-target profile which allows for the improvement of some of the most important hallmarks of the disease.

Protein tyrosine phosphatase 1B (PTP1B) as a potential therapeutic target for neurological disorders

Protein tyrosine phosphatase 1B (PTP1B) is a typical member of the PTP family, considered a direct negative regulator of several receptor and receptor-associated tyrosine kinases. This widely localized enzyme has been involved in the pathophysiology of several diseases. More recently, PTP1B has attracted attention in the field of neuroscience, since its activation in brain cells can lead to schizophrenia-like behaviour deficits, anxiety-like effects, neurodegeneration, neuroinflammation and depression. Conversely, PTP1B inhibition has been shown to prevent microglial activation, thus exerting a potent anti-inflammatory effect and has also shown potential to increase the cognitive process through the stimulation of hippocampal insulin, leptin and BDNF/TrkB receptors. Notwithstanding, most research on the clinical efficacy of targeting PTP1B has been developed in the field of obesity and type 2 diabetes mellitus (TD2M). However, despite the link existing between these metabolic alterations and neurodegeneration, no clinical trials assessing the neurological advantages of PTP1B inhibition have been performed yet. Preclinical studies, though, have provided strong evidence that targeting PTP1B could allow to reach different pathophysiological mechanisms at once. herefore, specific interventions or trials should be designed to modulate PTP1B activity in brain, since it is a promising strategy to decelerate or prevent neurodegeneration in aged individuals, among other neurological diseases. The present paper fails to include all neurological conditions in which PTP1B could have a role; instead, it focuses on those which have been related to metabolic alterations and neurodegenerative processes. Moreover, only preclinical data is discussed, since clinical studies on the potential of PTP1B inhibition for treating neurological diseases are still required.

Acutissimalignan B from traditional herbal medicine Daphne kiusiana var. atrocaulis (Rehd.) F. Maekawa inhibits neuroinflammation via NF-κB Signaling pathway

BACKGROUND

Emerging evidence indicates the important role of herbal medicine for neuroinflammation, which is closely associated with neurodegenerative diseases.

OBJECTIVE

To clarify the characteristics and primary mechanisms of action of the traditional herbal medicine Daphne kiusiana var. atrocaulis (Rehd.) F. Maekawa in neuroinflammation by phytochemistry and bioassays using both in vitro and in vivo assays.

METHODS

The chemical composition of D. kiusiana var. atrocaulis was clarified using multiple chromatography technologies and spectroscopic analysis. The anti-neuroinflammatory effects of the identified components were evaluated in LPS-induced BV-2 cells by monitoring the production of nitric oxide. C57BL/6 mice were used to construct a neuroinflammatory model by injecting LPS into the lateral ventricle of the brain. The most promising component was evaluated in vivo by measuring the number of Iba-1 cells and expression of inflammatory factors. Furthermore, the anti-neuroinflammatory mechanism involved in the activation of the NF-κB pathway was investigated using western blot and immunofluorescence.

RESULTS

Thirty-two constituents (1-32), including five new compounds, were successfully identified from D. kiusiana var. atrocaulis. Compounds 3, 5, 12-15, and 20 (IC50 values from 5.41 to 57.27 μM) could considerably inhibit the LPS-induced production of NO in BV-2 cells, displaying stronger anti-neuroinflammatory activities than that of minocycline (IC50 = 67.08 μM). The concentration of the most potential compound 13 (IC50 5.41 μM) was 5.4% of the ethyl acetate fraction. Acutissimalignan B (13) could reduce the mRNA expression of iNOs, TNF-α, IL-1β, and IL-6, inhibit the phosphorylation of IκBα, and inhibit the nuclear translocation of NK-κB p65 in BV-2 cells induced by LPS. Moreover, in the LPS-induced mouse model, compound 13 was found to exert anti-neuroinflammatory activity by attenuating the activation of microglia in the cortex and hippocampus, repressing the phosphorylation of IκBα, inhibiting the nuclear translocation of NK-κB p65, and decreasing the mRNA expression of iNOs, TNF-α, IL-1β, and IL-6 in the cortex.

CONCLUSION

We found that D. kiusiana var. atrocaulis had an inhibitory activity on neuroinflammation. In addition, the main active component (-)-acutissimalignan B (13) showed anti-neuroinflammatory effects in both in vivo and in vitro assays. Its mechanism of action may be associated with the inhibition of the NF-κB signaling pathway. Our current findings provide new information on D. kiusiana var. atrocaulis in the treatment of neuroinflammation.

PTP1B inhibitor alleviates deleterious microglial activation and neuronal injury after ischemic stroke by modulating the ER stress-autophagy axis via PERK signaling in microglia

Cerebral ischemia/reperfusion (IR) after ischemic stroke causes deleterious microglial activation. Protein tyrosine phosphatase 1B (PTP1B) exacerbates neuroinflammation, yet the effect of the inhibition on microglial activation and cerebral IR injury is unknown. A cerebral IR rat model was induced by middle cerebral artery occlusion (MCAO) and reperfusion. The PTP1B inhibitor, sc-222227, was administered intracerebroventricularly. Neurologic deficits, infarct volume, and brain water content were examined. An in vitro oxygen glucose deprivation/reoxygenation (OGD/R) model was established in primary microglia and BV-2 cells. Microglial activation/polarization, endoplasmic reticulum (ER) stress, autophagy, and apoptosis were detected using western blot, immunohistology, ELISA, and real-time PCR. Protein interaction was assessed by a proximity ligation assay. The results showed a significant increase in microglial PTP1B expression after IR injury. Sc-222227 attenuated IR-induced microglial activation, ER stress, and autophagy and promoted M2 polarization. Upon OGD/R, sc-222227 mitigated microglial activation by inhibiting ER stress-dependent autophagy, the effect of which was abolished by PERK activation, and PERK inhibition attenuated microglial activation. The PTP1B-phosphorylated PERK protein interaction was significantly increased after OGD/R, but decreased upon sc-222227 treatment. Finally, sc-222227 mitigated neuronal damage and neurologic deficits after IR injury. Treatment targeting microglial PTP1B might be a potential therapeutic strategy for ischemic stroke treatment.

The overexpression of TDP-43 in astrocytes causes neurodegeneration via a PTP1B-mediated inflammatory response

Background

Cytoplasmic inclusions of transactive response DNA binding protein of 43 kDa (TDP-43) in neurons and astrocytes are a feature of some neurodegenerative diseases, such as frontotemporal lobar degeneration with TDP-43 (FTLD-TDP) and amyotrophic lateral sclerosis (ALS). However, the role of TDP-43 in astrocyte pathology remains largely unknown.

Methods

To investigate whether TDP-43 overexpression in primary astrocytes could induce inflammation, we transfected primary astrocytes with plasmids encoding Gfp or TDP-43-Gfp. The inflammatory response and upregulation of PTP1B in transfected cells were examined using quantitative RT-PCR and immunoblot analysis. Neurotoxicity was analysed in a transwell coculture system of primary cortical neurons with astrocytes and cultured neurons treated with astrocyte-conditioned medium (ACM). We also examined the lifespan, performed climbing assays and analysed immunohistochemical data in pan-glial TDP-43-expressing flies in the presence or absence of a Ptp61f RNAi transgene.

Results

PTP1B inhibition suppressed TDP-43-induced secretion of inflammatory cytokines (interleukin 1 beta (IL-1β), interleukin 6 (IL-6) and tumour necrosis factor alpha (TNF-α)) in primary astrocytes. Using a neuron-astrocyte coculture system and astrocyte-conditioned media treatment, we demonstrated that PTP1B inhibition attenuated neuronal death and mitochondrial dysfunction caused by overexpression of TDP-43 in astrocytes. In addition, neuromuscular junction (NMJ) defects, a shortened lifespan, inflammation and climbing defects caused by pan-glial overexpression of TDP-43 were significantly rescued by downregulation of ptp61f (the Drosophila homologue of PTP1B) in flies.

Conclusions

These results indicate that PTP1B inhibition mitigates the neuronal toxicity caused by TDP-43-induced inflammation in mammalian astrocytes and Drosophila glial cells.

Regulation of peripheral and central immunity: Understanding the role of Src homology 2 domain-containing tyrosine phosphatases, SHP-1 & SHP-2

Protein tyrosine phosphorylation is a potent post-translational regulatory mechanism necessary for maintaining normal physiological functioning of immune cells and it is under the stringent control of antagonizing actions of Protein tyrosine phosphatases and kinases. Two such important Non-Receptor protein tyrosine phosphatases, SHP-1 and SHP-2, have been found to be expressed in immune cells and reported to be key regulators of immune cell development, functions, and differentiation by modulating the duration and amplitude of the downstream cascade transduced via receptors. They also have been conceded as the immune checkpoints & therapeutic targets and hence, it is important to understand their significance intricately. This review compares the roles of these two important cytoplasmic PTPs, SHP1 & SHP-2 in the regulation of peripheral as well as central immunity.

Natural Inhibitors on Over-Activation of Microglia from Herbals

Neuroinflammation manifested by over-activation of microglial cells plays an essential role in neurodegenerative diseases. Short-term activation of microglia can be beneficial, but chronically activated microglia can aggravate neuronal dysfunction possibly by secreting potentially cytotoxic substances such as tumor necrosis factor-alpha (TNF-α) and nitric oxide (NO), which can result in dysfunction and death of neurons. Therefore inhibiting over-activation of microglia and the production of cytotoxic intermediates may become an effective therapeutic approach for neuroinflammation. In this paper, we review our continuous research on natural inhibitors of over-activated microglia from traditional herbals, including flavonoids, lignans, sesquiterpene coumarins, and stilbenes.

Chandipura virus changes cellular miRNome in human microglial cells

Chandipura virus (CHPV) is a neurotropic virus, known to cause encephalitis in humans. The microRNAs (miRNA/miR) play an important role in the pathogenesis of viral infection. The present study is focused on the role of miRNAs during CHPV (strain 1653514) infection in human microglial cells. The deep sequencing of CHPV-infected human microglial cells identified a total of 12 differentially expressed miRNA (DEMs). To elucidate the role of DEMs, the target gene prediction, Gene Ontology term (GO Term), pathway enrichment analysis, and miRNA-messenger RNA (mRNA) interaction network analysis was performed. The GO terms and pathway enrichment analysis provided 146 enriched genes; which were involved in interferon response, cytokine and chemokine signaling. Further, the WGCNA (weighted gene coexpression network analysis) of the enriched genes were discretely categorized into three modules (blue, brown, and turquoise). The hub genes in the blue module may correlate to CHPV induced neuroinflammation. Altogether, the miRNA-mRNA interaction network and WGCNA study revealed the following pairs, hsa-miR-542-3p and FAF1, hsa-miR-92a-1-5p and MYD88, and hsa-miR-3187-3p and TNFRSF21, which may contribute to neuroinflammation during CHPV infection in human microglial cells.

The role of TCPTP on leptin effects on astrocyte morphology

Leptin and LPS has been implicated in the development of hypothalamic astrogliosis in rodents. Astrocytes, which are interconnected by gap junction proteins, have emerged as important players in the control of energy homeostasis exerted by the hypothalamus. To investigate the hypothesis of action of T-cell protein tyrosine phosphatase (TCPTP) on the astrocyte morphology, astrocytes from the hypothalamus of one-day-old rats were stimulated with leptin and LPS (used as a positive control). Leptin and LPS induced a marked increase in astrocyte size, an increase in Ptpn2 (TCPTP gene) and gap junction alpha-1 protein, - Gja1 (connexin 43 - CX43 gene) mRNA expression and a decrease in gap junction protein, alpha 6 - Gja6 (CX30 gene) mRNA expression. Remarkably, these effects on astrocytes morphology and connexins were prevented by Ptpn2 siRNA. Astrocytes are known to produce cytokines; here we show that TCPTP acts as an important regulator of the cytokines and it possesses a reciprocal interplay with protein tyrosine phosphatase 1B (PTP1B). Our findings demonstrate that leptin and LPS alter astrocyte morphology by increasing TCPTP, which in turn modulates connexin 30 (CX30) and connexin 43 (CX43) expression. TCPTP and PTP1B seem to act in the regulation of cytokine production in astrocytes.

Connecting Alzheimer's disease to diabetes: Underlying mechanisms and potential therapeutic targets

Alzheimer's disease (AD) is a risk factor for type 2 diabetes and vice versa, and a growing body of evidence indicates that these diseases are connected both at epidemiological, clinical and molecular levels. Recent studies have begun to reveal common pathogenic mechanisms shared by AD and type 2 diabetes. Impaired neuronal insulin signaling and endoplasmic reticulum (ER) stress are present in animal models of AD, similar to observations in peripheral tissue in T2D. These findings shed light into novel diabetes-related mechanisms leading to brain dysfunction in AD. Here, we review the literature on selected mechanisms shared between these diseases and discuss how the identification of such mechanisms may lead to novel therapeutic targets in AD. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'