Inducible Lentivirus-Mediated siRNA against TLR4 Reduces Nociception in a Rat Model of Bone Cancer Pain

Emergence of Small Interfering RNA-Based Gene Drugs for Various Diseases

Small molecule, peptide, and protein-based drugs have been developed over decades to treat various diseases. The importance of gene therapy as an alternative to traditional drugs has increased after the discovery of gene-based drugs such as Gendicine for cancer and Neovasculgen for peripheral artery disease. Since then, the pharma sector is focusing on developing gene-based drugs for various diseases. After the discovery of the RNA interference (RNAi) mechanism, the development of siRNA-based gene therapy has been accelerated immensely. siRNA-based treatment for hereditary transthyretin-mediated amyloidosis (hATTR) using Onpattro and acute hepatic porphyria (AHP) by Givlaari and three more FDA-approved siRNA drugs has set up a milestone and further improved the confidence for the development of gene therapeutics for a spectrum of diseases. siRNA-based gene drugs have more advantages over other gene therapies and are under study to treat different types of diseases such as viral infections, cardiovascular diseases, cancer, and many more. However, there are a few bottlenecks to realizing the full potential of siRNA-based gene therapy. They include chemical instability, nontargeted biodistribution, undesirable innate immune responses, and off-target effects. This review provides a comprehensive view of siRNA-based gene drugs: challenges associated with siRNA delivery, their potential, and future prospects.

Disentangling the enigmatic role of ephrin signaling in chronic pain: Moving towards future anti-pain therapeutics

Chronic pain is a common and debilitating condition with a huge social and economic burden worldwide. Currently, available drugs in clinics are not adequately effective and possess a variety of severe side effects leading to treatment withdrawal and poor quality of life. The ongoing search for new therapeutics with minimal side effects for chronic pain management remains a high research priority. Erythropoietin-producing human hepatocellular carcinoma cell receptor (Eph) is a tyrosine kinase receptor that is involved in neurodegenerative disorders, including pain. The Eph receptor interacts with several molecular switches, such as N methyl d-aspartate receptor (NMDAR), mitogen-activated protein kinase (MAPK), calpain 1, caspase 3, protein kinase a (PKA), and protein kinase Cy (PKCy), which in turn regulates pathophysiology of chronic pain. Here we highlight the emerging evidence of the Ephs/ephrin system as a possible near-future therapeutic target for the treatment of chronic pain and discuss the various mechanism of its involvement. We critically analyse the present status of Eph receptor system and conclude that extrapolating the pharmacological and genetic approaches using a strong therapeutic development framework could serve as next-generation analgesics for the management of chronic pain.

Multifarious Targets and Recent Developments in the Therapeutics for the Management of Bone Cancer Pain

Bone cancer pain (BCP) is a distinct pain state showing characteristics of both neuropathic and inflammatory pain. On average, almost 46% of cancer patients exhibit BCP with numbers flaring up to as high as 76% for terminally ill patients. Patients suffering from BCP experience a compromised quality of life, and the unavailability of effective therapeutics makes this a more devastating condition. In every individual cancer patient, the pain is driven by different mechanisms at different sites. The mechanisms behind the manifestation of BCP are very complex and poorly understood, which creates a substantial barrier to drug development. Nevertheless, some of the key mechanisms involved have been identified and are being explored further to develop targeted molecules. Developing a multitarget approach might be beneficial in this case as the underlying mechanism is not fixed and usually a number of these pathways are simultaneously dysregulated. In this review, we have discussed the role of recently identified novel modulators and mechanisms involved in the development of BCP. They include ion channels and receptors involved in sensing alteration of temperature and acidic microenvironment, immune system activation, sodium channels, endothelins, protease-activated receptors, neurotrophins, motor proteins mediated trafficking of glutamate receptor, and some bone-specific mechanisms. Apart from this, we have also discussed some of the novel approaches under preclinical and clinical development for the treatment of bone cancer pain.

Heme Causes Pain in Sickle Mice via Toll-Like Receptor 4-Mediated Reactive Oxygen Species- and Endoplasmic Reticulum Stress-Induced Glial Activation

Aims: Lifelong pain is a hallmark feature of sickle cell disease (SCD). How sickle pathobiology evokes pain remains unknown. We hypothesize that increased cell-free heme due to ongoing hemolysis activates toll-like receptor 4 (TLR4), leading to the formation of reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress. Together, these processes lead to spinal microglial activation and neuroinflammation, culminating in acute and chronic pain. Results: Spinal heme levels, TLR4 transcripts, oxidative stress, and ER stress were significantly higher in sickle mice than controls. In vitro, TLR4 inhibition in spinal cord microglial cells attenuated heme-induced ROS and ER stress. Heme treatment led to a time-dependent increase in the characteristic features of sickle pain (mechanical and thermal hyperalgesia) in both sickle and control mice; this effect was absent in TLR4-knockout sickle and control mice. TLR4 deletion in sickle mice attenuated chronic and hypoxia/reoxygenation (H/R)-evoked acute hyperalgesia. Sickle mice treated with the TLR4 inhibitor resatorvid; selective small-molecule inhibitor of TLR4 (TAK242) had significantly reduced chronic hyperalgesia and had less severe H/R-evoked acute pain with quicker recovery. Notably, reducing ER stress with salubrinal ameliorated chronic hyperalgesia in sickle mice. Innovation: Our findings demonstrate the causal role of free heme in the genesis of acute and chronic sickle pain and suggest that TLR4 and/or ER stress are novel therapeutic targets for treating pain in SCD. Conclusion: Heme-induced microglial activation via TLR4 in the central nervous system contributes to the initiation and maintenance of sickle pain via ER stress in SCD. Antioxid. Redox Signal. 34, 279-293.

Toll-like receptor 4 plays a key role in advanced glycation end products-induced M1 macrophage polarization

OBJECTIVE

This study was aimed to investigate the role of Toll-like receptor 4 (TLR4) in advanced glycation end products (AGEs)- induced macrophage polarization toward M1.

METHODS

Isolated primary macrophages were exposed to prepared AGEs at concentrations of 0, 2.5, 5 and 10 μmol/L. Macrophages were also exposed to hydrogen peroxide (H₂O₂) which provided exogenous reactive oxygen species (ROS). Receptor for AGEs (RAGE) was over-expressed by a vector. Specific siRNA silencing TLR4 and inhibitor TAK-242 were used to pre-treat the macrophages. Intracellular ROS was determined by DCFH-DA. Immunofluorescence staining was used to evaluate the expression of inducible nitric oxide synthase (iNOS) which is the marker of M1 macrophage phenotype. Real-time PCR was used to assess the mRNA expression level of TLR4 and RAGE. Protein expression levels of cytoplasmic RAGE, TLR4, nuclear signal transducers and activators of transcription 1 (STAT1) and phosphorylation levels of cytoplasmic STAT1 were evaluated by Western blotting. ELISA was used to measure concentrations of interleukin 6 (IL6), IL12 and tumor necrosis factor (TNF)α in supernatant of cell culture medium of macrophages.

RESULTS

AGEs significantly elevated intracellular ROS generation, expression levels of iNOS, cytoplasmic RAGE, TLR4, nuclear STAT1, phosphorylation levels of cytoplasmic STAT1, as well as IL6, IL12 and TNFα contents in a concentration-dependent manner. TLR4 silencing and inhibitor pre-treatment reduced expression levels of cytoplasmic RAGE, TLR4, phosphorylation of STAT1 and nuclear STAT1 in AGEs-exposed macrophages without affecting RAGE expression and intracellular ROS production levels. RAGE over-expression elevated both ROS and TLR4 expression levels in macrophages. TLR4 expression elevation was also found in H₂O₂-treat macrophages.

CONCLUSION

AGEs induced macrophage polarization toward M1 via activating RAGE/ROS/TLR4/STAT1 signaling pathway.

Pellino1 regulates neuropathic pain as well as microglial activation through the regulation of MAPK/NF-κB signaling in the spinal cord

Background

Spinal cord microglia plays a crucial role in the pathogenesis of neuropathic pain. However, the mechanisms underlying spinal microglial activation during neuropathic pain remain incompletely determined. Here, we investigated the role of Pellino1 (Peli1) and its interplay with spinal microglial activation in neuropathic pain.

Methods

In this study, we examined the effects of Peli1 on pain hypersensitivity and spinal microglial activation after chronic constriction injury (CCI) of the sciatic nerve in mice. The molecular mechanisms involved in Peli1-mediated hyperalgesia were determined by western blot, immunofluorescence, quantitative polymerase chain reaction (qPCR), and enzyme-linked immunosorbent assay (ELISA). We utilized immunoprecipitation to examine the ubiquitination of tumor necrosis factor receptor-associated factor 6 (TRAF6) following CCI. In addition, we explored the effect of Peli1 on BV2 microglial cells in response to lipopolysaccharide (LPS) challenge.

Results

We found that CCI induced a significant increase in the levels of Peli1, which was present in the great majority of microglia in the spinal dorsal horn. Our results showed that spinal Peli1 contributed to the induction and maintenance of CCI-induced neuropathic pain. The biochemical data revealed that CCI-induced Peli1 in the spinal cord significantly increased mitogen-activated protein kinase (MAPK) phosphorylation, activated nuclear factor kappa B (NF-κB), and enhanced the production of proinflammatory cytokines, accompanied by spinal microglial activation. Peli1 additionally was able to promote K63-linked ubiquitination of TRAF6 in the ipsilateral spinal cord following CCI. Furthermore, we demonstrated that Peli1 in microglial cells significantly enhanced inflammatory reactions after LPS treatment.

Conclusion

These results suggest that the upregulation of spinal Peli1 is essential for the pathogenesis of neuropathic pain via Peli1-dependent mobilization of spinal cord microglia, activation of MAPK/NF-κB signaling, and production of proinflammatory cytokines. Modulation of Peli1 may serve as a potential approach for the treatment of neuropathic pain.

PD-L1 is overexpressed on breast cancer stem cells through notch3/mTOR axis

The T-cell inhibitory molecule PD-L1 is expressed on a fraction of breast cancer cells. The distribution of PD-L1 on the different subpopulations of breast cancer cells is not well-defined. Our aim was to study the expression level of PD-L1 on breast cancer stem-like (CSC-like) cells and their differentiated-like counterparts. We used multi-parametric flow cytometry to measure PD-L1 expression in different subpopulations of breast cancer cells. Pathway inhibitors, quantitative immunofluorescence, cell sorting, and western blot were used to investigate the underlying mechanism of PD-L1 upregulation in CSC-like cells. Specifically, PD-L1 was overexpressed up to three folds on breast CSC-like cells compared with more differentiated-like cancer cells. Functional in vitro and in vivo assays show higher stemness of PD-L1^hi as compared with PD-L1^lo cells. Among different pathways examined, PD-L1 expression on CSCs was partly dependant on Notch, and/or PI3K/AKT pathway activation. The effect of Notch inhibitors on PD-L1 overexpression in CSCs was completely abrogated upon mTOR knockdown. Specific knockdown of different Notch receptors shows Notch3 as a mediator for PD-L1 overexpression on CSCs and important for maintaining their stemness. Indeed, Notch3 was found to be overexpressed on PD-L1^hi cells and specific knockdown of Notch3 abolished the effect of notch inhibitors and ligands on PD-L1 expression as well as mTOR activation. Our data demonstrated that overexpression of PD-L1 on CSCs is partly mediated by the notch pathway through Notch3/mTOR axis. We propose that these findings will help in a better design of anti-PD-L1 combination therapies to treat breast cancer effectively.

RNA control in pain: Blame it on the messenger

mRNA function is meticulously controlled. We provide an overview of the integral role that posttranscriptional controls play in the perception of painful stimuli by sensory neurons. These specialized cells, termed nociceptors, precisely regulate mRNA polarity, translation, and stability. A growing body of evidence has revealed that targeted disruption of mRNAs and RNA-binding proteins robustly diminishes pain-associated behaviors. We propose that the use of multiple independent regulatory paradigms facilitates robust temporal and spatial precision of protein expression in response to a range of pain-promoting stimuli. This article is categorized under: RNA in Disease and Development > RNA in Disease Translation > Translation Regulation RNA Turnover and Surveillance > Regulation of RNA Stability.

Interleukin-1 Receptor Associated Kinase 1 Mediates the Maintenance of Neuropathic Pain after Chronic Constriction Injury in Rats

Neuropathic pain (NP) has complicated pathogenesis as it mainly involves a lesion or dysfunction of the somatosensory nervous system and its clinical treatment remains challenging. Chronic constriction injury (CCI) model is a widely used neuropathic pain model and involved in mechanisms including both nerve inflammatory and injury. Cytokines and their receptors play essential roles in the occurrence and persistence of neuropathic pain, but the underlying mechanisms have not well been understood. Therefore, Interleukin-1 receptor-associated kinase 1 (IRAK1) is chosen to explore the possible mechanisms of NP. In the present study, IRAK1 was found to persistently increase in the dorsal root ganglion (DRG) and spinal cord (SC) during CCI detected by western blot. The staining further confirmed that IRAK1 was mainly co-located in the DRG astrocytes or SC neurons, but less in the DRG microglia or SC astrocytes. Moreover, the region of increased IRAK1 expression was observed in superficial laminae of the spinal dorsal horn, which was the nociceptive neuronal expression domain, suggesting that IRAK1 may mediated CCI-induced pain by nociceptive primary afferent. In addition, intrathecal injection of Toll-like receptor 4 (TLR4) inhibitor or IRAK1 siRNA decreased the expression of IRAK1 accompanied with the alleviation of CCI-induced neuropathic pain. The upregulation of p-NF-κB expression was reversed by IRAK1 siRNA in SC, and intrathecal injection of p-NF-κB inhibitor relieved neuropathic pain. Taking together, targeting IRAK1 may be a potential treatment for chronic neuropathic pain.

Lentiviral‑mediated inducible silencing of TLR4 attenuates neuropathic pain in a rat model of chronic constriction injury

An increasing body of evidence has indicated that spinal microglial Toll-like receptor 4 (TLR4) may serve a significant role in the development and maintenance of neuropathic pain (NP). In the present study, experiments were conducted to evaluate the contribution of a tetracycline inducible lentiviral-mediated delivery system for the expression of TLR4 small interfering (si)RNA to NP in rats with chronic constriction injury (CCI). Behavioral tests, including paw withdrawal latency and paw withdrawal threshold, and biochemical analysis of the spinal cord, including western blotting, reverse transcription-quantitative polymerase chain reaction and ELISA, were conducted following CCI to the sciatic nerve. Intrathecal administration of LvOn-si-TLR4 with doxycycline (Dox) attenuated allodynia and hyperalgesia. Biochemical analysis revealed that the mRNA and proteins levels of TLR4 were unregulated following CCI to the sciatic nerve, which was then blocked by intrathecal administration of LvOn-siTLR4 with Dox. The LvOn-siTLR4 was also demonstrated to have no effect on TLR4 or the pain response without Dox, which indicated that the expression of siRNA was Dox-inducible in the lentivirus delivery system. In conclusion, TLR4 may serve a significant role in neuropathy and the results of the present study provide an inducible lentivirus-mediated siRNA against TLR4 that may serve as a potential novel strategy to be applied in gene therapy for NP in the future.

Translocation Associated Membrane Protein 1 Contributes to Chronic Constriction Injury-Induced Neuropathic Pain in the Dorsal Root Ganglion and Spinal Cord in Rats

Neuropathic pain is a severe debilitating state caused by injury or dysfunction of somatosensory nervous system, and the clinical treatment is still challenging. Translocation associated membrane protein 1 (TRAM1), an adapter protein, participates in a variety of transduction pathways and mediates the biological functions such as cell proliferation, activation, and differentiation. However, whether TRAM1 is involved in the pathogenesis of neuropathic pain is still unclear. In our study, we reported the role of TRAM1 in the maintenance of neuropathic pain induced by chronic constriction injury (CCI) on rats. By western blot and staining, we found that TRAM1 increased in the dorsal root ganglion (DRG) neurons and spinal cord (SC) neurons after CCI. Being similar to IB4-, CGRP-positive expressed area, TRAM1 also expressed in the superficial laminae of the spinal cord dorsal horn (SCDH), suggesting it was related to the innervations of the primary afferents. Moreover, intrathecal injection of TRAM1 siRNA or Toll-like receptor 4 (TLR4) inhibitor induced low expression of TRAM1 in SC, which alleviated the pain response induced by CCI. The upregulation of p-NF-κB expression was reversed by TRAM1 siRNA in SC and DRG, and intrathecal injection of p-NF-κB inhibitor relieved neuropathic pain. All the data indicated that TRAM1 could take part in CCI-induced pain and might be a potential treatment for chronic neuropathic pain.

Effects of small interfering RNA targeting TLR4 on expressions of adipocytokines in obstructive sleep apnea hyponea syndrome with hypertension in a rat model

We explored the effects of RNA interference-mediated silencing of TLR4 gene on expressions of adipocytokines in obstructive sleep apnea hyponea syndrome (OSAS) with hypertension in a rat model. Systolic blood pressure of caudal artery and physiological changes were observed when establishing rat models of OSAS with hypertension. Mature rat adipocytes were induced from separated and cultured primary rat adipocytes. To transfect rat mature adipocytes, TLR4 siRNA group and negative control (NC) siRNA group were established. Expressions of TLR4 mRNA of adipocytes were examined after silenced by siRNA by quantitative real-time polymerase chain reaction (qRT-PCR). By enzyme-linked immunosorbent assay (ELISA), expressions of inflammatory cytokines, and adipocytokines of adipocytes were detected. Blood pressure in rat caudal artery was higher in the intermittent hypoxia group than that of the blank control group by 29.87 mmHg, and cardiocytes in the former group showed physiological changes, which indicated successful establishment of rat models of OSAS with hypertension. Red particles could be seen in mature rat adipocytes when stained with Oil Red O. Transfection of TLR4 mRNA was significantly suppressed in the TLR4 siRNA group, which didn't happen in the untransfected control group. Rats in the TLR4 siRNA group had significantly reduced expressions of such inflammatory cytokines as interleukin-6 (IL-6), interleukin-8 (IL-8), and tumor necrosis factor-α (TNF-α) and such adipocytokines as visfatin, adiponectin (ADN), and leptin than those in the untransfected control group. RNA interference-mediated silencing of TLR4 gene could regulate occurrence and development of OSAS with hypertension in rats by downregulating expressions of adipocytokines.

Upregulation of Spinal Voltage-Dependent Anion Channel 1 Contributes to Bone Cancer Pain Hypersensitivity in Rats

Voltage-dependent anion channel 1 (VDAC1) is thought to contribute to the progression of tumor development. However, whether VDAC1 contributes to bone cancer pain remains unknown. In this study, we found that the expression of VDAC1 was upregulated in the L2-5 segments of the spinal dorsal horn at 2 and 3 weeks after injection of tumor cells into the tibial cavity. Intrathecal injection of a VDAC1 inhibitor significantly reversed the pain hypersensitivity and reduced the over-expression of Toll-like receptor 4 (TLR4). Intrathecal injection of minocycline, an inhibitor of microglia, also attenuated the pain hypersensitivity of rat models of bone cancer pain. These results suggest that VDAC1 plays a significant role in the development of complicated cancer pain, possibly by regulating the expression of TLR4.

Small non-coding RNAs-based bone regulation and targeting therapeutic strategies

Small non-coding RNAs, which are 20-25 nucleotide ribonucleic acids, have emerged as an important transformation in the biological evolution over almost three decades. microRNAs (miRNAs) and short interfering RNAs (siRNAs) are two significant categories of the small RNAs that exert important effects on bone endocrinology and skeletology. Therefore, clarifying the expression and function of these important molecules in bone endocrine physiology and pathology is of great significance for improving their potential therapeutic value for metabolism-associated bone diseases. In the present review, we highlight the recent advances made in understanding the function and molecular mechanism of these small non-coding RNAs in bone metabolism, especially their potentially therapeutic values in bone-related diseases.

The Walker 256 Breast Cancer Cell- Induced Bone Pain Model in Rats

The majority of patients with terminal breast cancer show signs of bone metastasis, the most common cause of pain in cancer. Clinically available drug treatment options for the relief of cancer-associated bone pain are limited due to either inadequate pain relief and/or dose-limiting side-effects. One of the major hurdles in understanding the mechanism by which breast cancer causes pain after metastasis to the bones is the lack of suitable preclinical models. Until the late twentieth century, all animal models of cancer induced bone pain involved systemic injection of cancer cells into animals, which caused severe deterioration of animal health due to widespread metastasis. In this mini-review we have discussed details of a recently developed and highly efficient preclinical model of breast cancer induced bone pain: Walker 256 cancer cell- induced bone pain in rats. The model involves direct localized injection of cancer cells into a single tibia in rats, which avoids widespread metastasis of cancer cells and hence animals maintain good health throughout the experimental period. This model closely mimics the human pathophysiology of breast cancer induced bone pain and has great potential to aid in the process of drug discovery for treating this intractable pain condition.

Obesity Takes Its Toll on Visceral Pain: High-Fat Diet Induces Toll-Like Receptor 4-Dependent Visceral Hypersensitivity

Exposure to high-fat diet induces both, peripheral and central alterations in TLR4 expression. Moreover, functional TLR4 is required for the development of high-fat diet-induced obesity. Recently, central alterations in TLR4 expression have been associated with the modulation of visceral pain. However, it remains unknown whether there is a functional interaction between the role of TLR4 in diet-induced obesity and in visceral pain. In the present study we investigated the impact of long-term exposure to high-fat diet on visceral pain perception and on the levels of TLR4 and Cd11b (a microglial cell marker) protein expression in the prefrontal cortex (PFC) and hippocampus. Peripheral alterations in TLR4 were assessed following the stimulation of spleenocytes with the TLR4-agonist LPS. Finally, we evaluated the effect of blocking TLR4 on visceral nociception, by administering TAK-242, a selective TLR4-antagonist. Our results demonstrated that exposure to high-fat diet induced visceral hypersensitivity. In parallel, enhanced TLR4 expression and microglia activation were found in brain areas related to visceral pain, the PFC and the hippocampus. Likewise, peripheral TLR4 activity was increased following long-term exposure to high-fat diet, resulting in an increased level of pro-inflammatory cytokines. Finally, TLR4 blockage counteracted the hyperalgesic phenotype present in mice fed on high-fat diet. Our data reveal a role for TLR4 in visceral pain modulation in a model of diet-induced obesity, and point to TLR4 as a potential therapeutic target for the development of drugs to treat visceral hypersensitivity present in pathologies associated to fat diet consumption.