Downstream Signaling Research Articles

A mechanistic PK/PD model of AZD0171 (anti-LIF) to support Phase II dose selection.

AZD0171 (INN: Falbikitug) is being developed as a humanized monoclonal antibody (mAb), immunoglobulin G subclass 1 (IgG1), which binds specifically to the immunosuppressive human cytokine leukemia inhibitory factor (LIF) and inhibits downstream signaling by blocking recruitment of glycoprotein 130 (gp130) to the LIF receptor (LIFR) subunit (gp190) and the phosphorylation of signal transducer and activator of transcription 3 (STAT3) and is intended to treat adult participants with advanced solid tumors. LIF is a pleiotropic cytokine (and a member of the IL-6 family of cytokines) involved in many physiological and pathological processes and is highly expressed in a subset of solid tumors, including non-small cell lung cancer (NSCLC), colon, ovarian, prostate, and pancreatic cancer. The aim of this work was to develop a mechanistic PK/PD model to investigate the effect of AZD0171 on tumor LIF levels, predict the level of downstream signaling complex (LIF:LIFR:gp130) inhibition, and examine the dose-response relationship to support dose selection for a Phase II clinical study. Modeling results show that tumor LIF is inhibited in a dose-dependent manner with >90% inhibition for 95% of patients at the Phase II clinical dose of 1500 mg Q2W.

Synaptic Plasticity in the Injured Brain Depends on the Temporal Pattern of Stimulation.

Neurostimulation protocols are increasingly used as therapeutic interventions, including for brain injury. In addition to the direct activation of neurons, these stimulation protocols are also likely to have downstream effects on those neurons' synaptic outputs. It is well known that alterations in the strength of synaptic connections (long-term potentiation, LTP; long-term depression, LTD) are sensitive to the frequency of stimulation used for induction; however, little is known about the contribution of the temporal pattern of stimulation to the downstream synaptic plasticity that may be induced by neurostimulation in the injured brain. We explored interactions of the temporal pattern and frequency of neurostimulation in the normal cerebral cortex and after mild traumatic brain injury (mTBI), to inform therapies to strengthen or weaken neural circuits in injured brains, as well as to better understand the role of these factors in normal brain plasticity. Whole-cell (WC) patch-clamp recordings of evoked postsynaptic potentials in individual neurons, as well as field potential (FP) recordings, were made from layer 2/3 of visual cortex in response to stimulation of layer 4, in acute slices from control (naive), sham operated, and mTBI rats. We compared synaptic plasticity induced by different stimulation protocols, each consisting of a specific frequency (1 Hz, 10 Hz, or 100 Hz), continuity (continuous or discontinuous), and temporal pattern (perfectly regular, slightly irregular, or highly irregular). At the individual neuron level, dramatic differences in plasticity outcome occurred when the highly irregular stimulation protocol was used at 1 Hz or 10 Hz, producing an overall LTD in controls and shams, but a robust overall LTP after mTBI. Consistent with the individual neuron results, the plasticity outcomes for simultaneous FP recordings were similar, indicative of our results generalizing to a larger scale synaptic network than can be sampled by individual WC recordings alone. In addition to the differences in plasticity outcome between control (naive or sham) and injured brains, the dynamics of the changes in synaptic responses that developed during stimulation were predictive of the final plasticity outcome. Our results demonstrate that the temporal pattern of stimulation plays a role in the polarity and magnitude of synaptic plasticity induced in the cerebral cortex while highlighting differences between normal and injured brain responses. Moreover, these results may be useful for optimization of neurostimulation therapies to treat mTBI and other brain disorders, in addition to providing new insights into downstream plasticity signaling mechanisms in the normal brain.

Cell autonomous functions of CD47 in regulating cellular plasticity and metabolic plasticity.

CD47 is a ubiquitously expressed cell surface receptor, which is widely known for preventing macrophage-mediated phagocytosis by interacting with signal regulatory protein α (SIRPα) on the surface of macrophages. In addition to its role in phagocytosis, emerging studies have reported numerous noncanonical functions of CD47 that include regulation of various cellular processes such as proliferation, migration, apoptosis, differentiation, stress responses, and metabolism. Despite lacking an extensive cytoplasmic signaling domain, CD47 binds to several cytoplasmic proteins, particularly upon engaging with its secreted matricellular ligand, thrombospondin 1. Indeed, the regulatory functions of CD47 are greatly influenced by its interacting partners. These interactions are often cell- and context-specific, adding a further level of complexity. This review addresses the downstream cell-intrinsic signaling pathways regulated by CD47 in various cell types and environments. Some of the key pathways modulated by this receptor include the PI3K/AKT, MAPK/ERK, and nitric oxide signaling pathways, as well as those implicated in glucose, lipid, and mitochondrial metabolism. These pathways play vital roles in maintaining tissue homeostasis, highlighting the importance of understanding the phagocytosis-independent functions of CD47. Given that CD47 expression is dysregulated in a variety of cancers, improving our understanding of the cell-intrinsic signals regulated by this molecule will help advance the development of CD47-targeted therapies.

BUB1b impairs chemotherapy sensitivity via resistance to ferroptosis in lung adenocarcinoma

BUB1 mitotic checkpoint serine/threonine kinase B (BUB1b) has been unequivocally identified as an oncogene in various cancers. However, the potential mechanism by which BUB1b orchestrates the progression of lung adenocarcinoma (LUAD) remains unclear. Here we found that both the transcript and protein levels of BUB1b were dramatically upregulated in tumor tissues and contributed to the dismal prognosis of LUAD patients. Moreover, gain- and loss-of-function assays, conducted both in vitro and in vivo, confirmed that BUB1b enhanced the viability of LUAD cells. Mechanistically, BUB1b forms a complex with OTUD3 and NRF2 and stabilizes the downstream NRF2 signaling pathway to facilitate insensitivity to ferroptosis and chemotherapy. In BALB/c nude mice bearing subcutaneous tumors that overexpress BUB1b, a combined strategy of ML385 targeting and chemotherapy achieved synergistic effects, inhibiting tumor growth and obviously improving survival. Taken together our study uncovered the underlying mechanism by which BUB1b promotes the progression of LUAD and proposed a novel strategy to enhance the efficacy of chemotherapy.

Knockdowns of CD3zeta chain in Primary NK Cells Illustrate Modulation of Antibody-Dependent Cellular Cytotoxicity against Human Immunodeficiency Virus-1.

Multifaceted natural killer (NK) cell activities are indispensable for controlling human immunodeficiency virus (HIV)-1 transmission and pathogenesis. Among the diverse functions of NK cells, antibody-dependent cellular cytotoxicity (ADCC) has been shown to predict better HIV-1 protection (1-3). ADCC is initiated by the engagement of an Fcg receptor CD16 with an Fc portion of the antibody, leading to phosphorylation of the CD3z chain (CD3) and Fc receptor g chain (FcRg) as well as downstream signaling activation. Though CD3 and FcR were thought to have overlapping roles in NK cell ADCC, several groups have reported that CD3-mediated signals trigger a more robust ADCC (4-8). However, few studies have illustrated the direct contribution of CD3z in HIV-1-specific ADCC. To further understand the roles played by CD3 in HIV-1-specific ADCC, we developed a CD3z knockdown system in primary human NK cells. We observed that HIV-1-specific ADCC was inhibited by CD3z perturbation. In summary, we demonstrated that CD3 is important for eliciting HIV-1-specific ADCC, and this dynamic can be utilized for NK cell immunotherapeutics against HIV-1 infection and other diseases.

Manuka Honey Inhibits Human Breast Cancer Progression in Preclinical Models

Manuka honey (MH) exhibits potential antitumor activity in preclinical models of a number of human cancers. Treatment in vitro with MH at concentrations ranging from 0.3 to 5.0% (w/v) led to significant dose-dependent inhibition of proliferation of human breast cancer MCF-7 cells, but anti-proliferative effects of MH were less pronounced in MDA-MB-231 breast cancer cells. Effects of MH were also tested on non-malignant human mammary epithelial cells (HMECs) at 2.5% w/v, and it was found that MH reduced the proliferation of MCF-7 cells but not that of HMECs. Notably, the antitumor activity of MH was in the range of that exerted by treatment of MCF-7 cells with the antiestrogen tamoxifen. Further, MH treatment stimulated apoptosis of MCF-7 cells in vitro, with most cells exhibiting acute and significant levels of apoptosis that correlated with PARP activation. Additionally, the effects of MH induced the activation of AMPK and inhibition of AKT/mTOR downstream signaling. Treatment of MCF7 cells with increased concentrations of MH induced AMPK phosphorylation in a dose-dependent manner that was accompanied by inhibition of phosphorylation of AKT and mTOR downstream effector protein S6. In addition, MH reduced phosphorylated STAT3 levels in vitro, which may correlate with MH and AMPK-mediated anti-inflammatory properties. Further, in vivo, MH administered alone significantly inhibited the growth of established MCF-7 tumors in nude mice by 84%, resulting in an observable reduction in tumor volume. Our findings highlight the need for further research into the use of natural compounds, such as MH, for antitumor efficacy and potential chemoprevention and investigation of molecular pathways underlying these actions.

C-JUN overexpressing CAR-T cells in acute myeloid leukemia: preclinical characterization and phase I trial

Chimeric antigen receptor (CAR) T cells show suboptimal efficacy in acute myeloid leukemia (AML). We find that CAR T cells exposed to myeloid leukemia show impaired activation and cytolytic function, accompanied by impaired antigen receptor downstream calcium, ZAP70, ERK, and C-JUN signaling, compared to those exposed to B-cell leukemia. These defects are caused in part by the high expression of CD155 by AML. Overexpressing C-JUN, but not other antigen receptor downstream components, maximally restores anti-tumor function. C-JUN overexpression increases costimulatory molecules and cytokines through reinvigoration of ERK or transcriptional activation, independent of anti-exhaustion. We conduct an open-label, non-randomized, single-arm, phase I trial of C-JUN-overexpressing CAR-T in AML (NCT04835519) with safety and efficacy as primary and secondary endpoints, respectively. Of the four patients treated, one has grade 4 (dose-limiting toxicity) and three have grade 1–2 cytokine release syndrome. Two patients have no detectable bone marrow blasts and one patient has blast reduction after treatment. Thus, overexpressing C-JUN endows CAR-T efficacy in AML.

Unexpected Diagnosis of WHIM syndrome in Refractory Autoimmune Cytopenia

WHIM (Warts, Hypogammaglobulinemia, Infections, Myelokathexis) syndrome is a rare primary immunodeficiency predominantly caused by heterozygous gain-of-function mutations in the c-terminus of the gene CXCR4. These CXCR4 variants display impaired receptor trafficking with persistence of the CXCR4 receptor on the surface resulting in hyperactive downstream signaling following CXCL12 stimulation. In turn, this results in defective lymphoid differentiation, and reduced blood neutrophil and lymphocyte numbers. Here we report a CXCR4 mutation that in two members of a kindred, led to life-long autoimmunity and lymphoid hypertrophy as the primary clinical manifestations of WHIM syndrome. We examine the functional effects of this mutation, and how these have affected phosphorylation, activation, and receptor internalization.

Species-specific IL-1β is an inflammatory sensor of Seneca Valley Virus 3C Protease.

Inflammasomes play pivotal roles in inflammation by processing and promoting the secretion of IL-1β. Caspase-1 is involved in the maturation of IL-1β and IL-18, while human caspase-4 specifically processes IL-18. Recent structural studies of caspase-4 bound to Pro-IL-18 reveal the molecular basis of Pro-IL-18 activation by caspase-4. However, the mechanism of caspase-1 processing of pro-IL-1β and other IL-1β-converting enzymes remains elusive. Here, we observed that swine Pro-IL-1β (sPro-IL-1β) exists as an oligomeric precursor unlike monomeric human Pro-IL-1β (hPro-IL-1β). Interestingly, Seneca Valley Virus (SVV) 3C protease cleaves sPro-IL-1β to produce mature IL-1β, while it cleaves hPro-IL-1β but does not produce mature IL-1β in a specific manner. When the inflammasome is blocked, SVV 3C continues to activate IL-1β through direct cleavage in porcine alveolar macrophages (PAMs). Through molecular modeling and mutagenesis studies, we discovered that the pro-domain of sPro-IL-1β serves as an 'exosite' with its hydrophobic residues docking into a positively charged 3C protease pocket, thereby directing the substrate to the active site. The cleavage of swine IL-1β (sIL-1β) generates a monomeric and active form of sIL-1β, initiating the downstream signaling. Thus, these studies provide IL-1β is an inflammatory sensor that directly detects viral protease through an independent pathway operating in parallel with host inflammasomes.

Norepinephrine Neurons in the Nucleus of the Solitary Tract Suppress Luteinizing Hormone Secretion in Female Mice.

Stress impairs fertility, at least in part, via inhibition of gonadotropin secretion. Luteinizing hormone (LH) is an important gonadotropin that is released in a pulsatile pattern in males and in females throughout the majority of the ovarian cycle. Several models of stress, including acute metabolic stress, suppress LH pulses via inhibition of neurons in the arcuate nucleus of the hypothalamus that co-express kisspeptin, neurokinin B, and dynorphin (termed KNDy cells) which form the pulse generator. The mechanism for inhibition of KNDy neurons during stress, however, remains a significant outstanding question. Here, we investigated a population of catecholamine neurons in the nucleus of the solitary tract (NTS), marked by expression of the enzyme dopamine beta-hydroxylase (DBH), in female mice. First, we found that a subpopulation of DBH neurons in the NTS are activated (express c-Fos) during metabolic stress. Then, using chemogenetics we determined that activation of these cells is sufficient to suppress LH pulses, augment corticosterone secretion, and induce sickness-like behavior. In subsequent studies, we identified evidence for suppression of KNDy cells (rather than downstream signaling pathways) and determined that the suppression of LH pulses was not dependent on the acute rise in glucocorticoids. Together these data support the hypothesis that DBH cells in the NTS are important for regulation of neuroendocrine and behavioral responses to stress.Significance Statement Stress impairs fertility, at least in part, via inhibition of gonadotropin secretion. The gonadotropin luteinizing hormone (LH) is secreted in a pulsatile pattern in males and females throughout most of the ovarian cycle to support gamete development and sex steroid production in both sexes. Here, we investigated a population of catecholamine neurons in the nucleus of the solitary tract (NTS) for their role in regulation of pulsatile LH secretion. We demonstrate that these neurons are sufficient to suppress pulsatile LH secretion via inhibition of kisspeptin neurons in ovariectomized mice. Moreover, these NTS neurons are also sufficient to augment corticosterone concentrations and induce sickness-like behavior, which raises the possibility that these neurons are important for neuroendocrine and behavioral responses during stress.

Hepatocyte-specific EGFR deletion promotes fibrosis but has no effect on steatosis in fast food diet model of MASLD

MASLD has become the most prevalent chronic liver disorder, with no approved treatment. Our previous work demonstrated the efficacy of a pan-ErbB inhibitor, Canertinib, in reducing steatosis and fibrosis in a murine fast-food diet (FFD) model of MASLD. The current study explores the effects of hepatocyte-specific ErbB1 (i.e. EGFR) deletion in the FFD model. EGFRflox/flox mice, treated with AAV8-TBG-CRE to delete EGFR specifically in hepatocytes (EGFR-KO), were fed either a chow-diet or FFD for 2 or 5-months. Hepatocyte-specific EGFR deletion reduced serum triglyceride levels but did not prevent steatosis. Surprisingly, hepatic fibrosis was increased in EGFR-KO mice in the long-term study, which correlated with activation of TGFβ1/fibrosis signaling pathways. Further, nuclear levels of some of the major MASLD regulating transcription factors (SREBP1, PPARγ, PPARα, and HNF4α) were altered in FFD-fed EGFR-KO mice. Transcriptomic analysis revealed significant alteration of lipid metabolism pathways in EGFR-KO mice with changes in several relevant genes, including downregulation of fatty-acid synthase and induction of lipolysis gene, Pnpla2, without impacting overall steatosis. Interestingly, EGFR downstream signaling mediators, including AKT, remain activated in EGFR-KO mice, which correlated with increased activity pattern of other receptor tyrosine kinases, including ErbB3/MET, in transcriptomic analysis. Lastly, Canertinib treatment in EGFR-KO mice, which inhibits all ErbB receptors, successfully reduced steatosis, suggesting the compensatory roles of other ErbB receptors in supporting MASLD without EGFR. Hepatocyte-specific EGFR-KO did not impact steatosis, but enhanced fibrosis in the FFD model of MASLD. Gene-networks associated with lipid metabolism were greatly altered in EGFR-KO, but phenotypic effects might be compensated by alternate signaling-pathways.

Alzheimer's disease linked Aβ42 exerts product feedback inhibition on γ-secretase impairing downstream cell signaling.

Amyloid β (Aβ) peptides accumulating in the brain are proposed to trigger Alzheimer's disease (AD). However, molecular cascades underlying their toxicity are poorly defined. Here, we explored a novel hypothesis for Aβ42 toxicity that arises from its proven affinity for γ-secretases. We hypothesized that the reported increases in Aβ42, particularly in the endolysosomal compartment, promote the establishment of a product feedback inhibitory mechanism on γ-secretases, and thereby impair downstream signaling events. We conducted kinetic analyses of γ-secretase activity in cell-free systems in the presence of Aβ, as well as cell-based and ex vivo assays in neuronal cell lines, neurons, and brain synaptosomes to assess the impact of Aβ on γ-secretases. We show that human Aβ42 peptides, but neither murine Aβ42 nor human Aβ17-42 (p3), inhibit γ-secretases and trigger accumulation of unprocessed substrates in neurons, including C-terminal fragments (CTFs) of APP, p75, and pan-cadherin. Moreover, Aβ42 treatment dysregulated cellular homeostasis, as shown by the induction of p75-dependent neuronal death in two distinct cellular systems. Our findings raise the possibility that pathological elevations in Aβ42 contribute to cellular toxicity via the γ-secretase inhibition, and provide a novel conceptual framework to address Aβ toxicity in the context of γ-secretase-dependent homeostatic signaling.

Astragalus mongholicus bunge and panax notoginseng formula (A&P) improves renal fibrosis in UUO mice via inhibiting the long non-coding RNA A330074K22Rik and downregulating ferroptosis signaling

BackgroundChronic kidney disease (CKD) and its associated end-stage renal disease (ESRD) are significant health problems that pose a threat to human well-being. Renal fibrosis is a common feature and ultimate pathological outcome of various CKD leading to ESRD. The Astragalus mongholicus Bunge and Panax notoginseng formula (A&P) is a refined compound formulated by our research group, which has been clinically administered for over a decade and has demonstrated the ability to improve the inflammatory state of various acute or chronic kidney diseases. However, the underlying mechanism by which A&P ameliorates renal fibrosis remains unclear.MethodsWe established a mouse model by surgically ligating the unilateral ureter to induce renal injury in vivo. And we utilized renal in situ electroporation of a plasmid with low LncRNA A33 expression to establish the unilateral ureteral obstruction(UUO)mouse model. In vitro, we stimulated primary tubular epithelial cells(pTEC) injury using TGF-β1, siRNA-A33, and pcDNA3.1-A33 plasmids were transfected into pTECs to respectively knockdown and overexpress LncRNA A33, and both in vitro and in vivo models were intervened with A&P.ResultsThe results demonstrated that A&P effectively alleviated renal fibrosis in mice. Subsequent findings indicated high expression of LncRNA A33 in the kidneys of UUO mice and TGF-β1-induced renal tubular cells. In situ, renal electroporation of a plasmid with reduced LncRNA A33 expression revealed that inhibiting LncRNA A33 significantly improved renal fibrosis in UUO mice. Moreover, A&P effectively suppressed LncRNA A33 expression both in vitro and in vivo. Subsequent downregulation of LncRNA A33 in renal tubular epithelial cells resulted in the downregulation of numerous fibrotic markers, a significant inhibition of LncRNA A33, and a notable reduction in downstream ferroptosis signaling. Cell experiments demonstrated that A&P improved renal fibrosis in UUO mice by inhibiting LncRNA A33 and downregulating ferroptosis signaling.ConclusionThrough the inhibition of LncRNA A33 and subsequent downregulation of ferroptosis signaling, A&P showed potential as a therapeutic approach for improving renal fibrosis in UUO mice, providing a potential treatment avenue for CKD.

Alzheimer’s disease linked Aβ42 exerts product feedback inhibition on γ-secretase impairing downstream cell signaling

Alzheimer’s disease linked Aβ42 exerts product feedback inhibition on γ-secretase impairing downstream cell signaling

GPR34 senses demyelination to promote neuroinflammation and pathologies.

Sterile neuroinflammation is a major driver of multiple neurological diseases. Myelin debris can act as an inflammatory stimulus to promote inflammation and pathologies, but the mechanism is poorly understood. Here, we showed that lysophosphatidylserine (LysoPS)-GPR34 axis played a critical role in microglia-mediated myelin debris sensing and the subsequent neuroinflammation. Myelin debris-induced microglia activation and proinflammatory cytokine expression relied on its lipid component LysoPS. Both myelin debris and LysoPS promoted microglia activation and the production of proinflammatory cytokines via GPR34 and its downstream PI3K-AKT and ERK signaling. In vivo, reducing the content of LysoPS in myelin or inhibition of GPR34 with genetic or pharmacological approaches reduced neuroinflammation and pathologies in the mouse models of multiple sclerosis and stroke. Thus, our results identify GPR34 as a key receptor to sense demyelination and CNS damage and promote neuroinflammation, and suggest it as a potential therapeutic target for demyelination-associated diseases.

Phosphorylation of CAX transporters controls Ca2+ homeostasis

Plants rely on a sophisticated innate immune system to recognize and defend against invading pathogens. The first line of plant innate immunity called pattern-triggered immunity (PTI) is initiated upon detection of pathogen-associated molecular patterns (PAMPs) by plasma membrane-localized pattern recognition receptors (PRRs) (Jones and Dangl, 2006). A well-characterized PRR is the Arabidopsis receptor-like kinase (RLK) FLS2, which complexes with the co-receptor BAK1 to detect the bacterial PAMP flagellin (or its major epitope flg22) (Zipfel, 2014). Downstream of PAMP-triggered PRR activation, the receptor-like cytoplasmic kinases (RLCKs), such as BIK1 and RIPK, associate with and are activated by PRRs to trigger diverse downstream immune signaling events, including reactive oxygen species (ROS) burst, phosphatidic acid (PA) production, increase of cytoplasmic calcium ([Ca2+]cyt) concentration, and activation of mitogen-activated protein kinase (MAPK) cascades, which collectively lead to the establishment of plant PTI (Bigeard et al., 2015).

The LCLAT1/LYCAT acyltransferase is required for EGF-mediated phosphatidylinositol-3,4,5-trisphosphate generation and Akt signalling.

Receptor tyrosine kinases such as epidermal growth factor receptor (EGFR) stimulate phosphoinositide 3-kinases (PI3Ks) to convert phosphatidylinositol-4,5-bisphosophate [PtdIns(4,5)P2] into phosphatidylinositol-3,4,5-trisphosphate [PtdIns(3,4,5)P3]. PtdIns(3,4,5)P3 then remodels actin and gene expression, and boosts cell survival and proliferation. PtdIns(3,4,5)P3 partly achieves these functions by triggering activation of the kinase Akt, which phosphorylates targets like Tsc2 and GSK3β. Consequently, unchecked upregulation of PtdIns(3,4,5)P3-Akt signalling promotes tumour progression. Interestingly, 50-70% of PtdIns and PtdInsPs have stearate and arachidonate at sn-1 and sn-2 positions of glycerol, respectively, forming a species known as 38:4-PtdIns/PtdInsPs. LCLAT1 and MBOAT7 acyltransferases partly enrich PtdIns in this acyl format. We previously showed that disruption of LCLAT1 lowered PtdIns(4,5)P2 levels and perturbed endocytosis and endocytic trafficking. However, the role of LCLAT1 in receptor tyrosine kinase and PtdIns(3,4,5)P3 signaling was not explored. Here, we show that LCLAT1 silencing in MDA-MB-231 and ARPE-19 cells abated the levels of PtdIns(3,4,5)P3 in response to EGF signalling. Importantly, LCLAT1-silenced cells were also impaired for EGF-driven and insulin-driven Akt activation and downstream signalling. Thus, our work provides first evidence that the LCLAT1 acyltransferase is required for receptor tyrosine kinase signalling.

A new light on PLCβ!

In this issue of Cell Chemical Biology, Kim etal.1 present a novel optogenetic tool, opto-PLCβ, to control PLCβ signaling optically. In addition to eliciting PIP2 hydrolysis and downstream signaling in cells, opto-PLCβ also enabled probing the impact of PLCβ signaling on amygdala synaptic plasticity and fear learning in mice.

Sphinganine recruits TLR4 adaptors in macrophages and promotes inflammation in murine models of sepsis and melanoma

After recognizing its ligand lipopolysaccharide, Toll-like receptor 4 (TLR4) recruits adaptor proteins to the cell membrane, thereby initiating downstream signaling and triggering inflammation. Whether this recruitment of adaptor proteins is dependent solely on protein-protein interactions is unknown. Here, we report that the sphingolipid sphinganine physically interacts with the adaptor proteins MyD88 and TIRAP and promotes MyD88 recruitment in macrophages. Myeloid cell-specific deficiency in serine palmitoyltransferase long chain base subunit 2, which encodes the key enzyme catalyzing sphingolipid biosynthesis, decreases the membrane recruitment of MyD88 and inhibits inflammatory responses in in vitro bone marrow-derived macrophage and in vivo sepsis models. In a melanoma mouse model, serine palmitoyltransferase long chain base subunit 2 deficiency decreases anti-tumor myeloid cell responses and increases tumor growth. Therefore, sphinganine biosynthesis is required for the initiation of TLR4 signal transduction and serves as a checkpoint for macrophage pattern recognition in sepsis and melanoma mouse models.

Potential Exacerbation of Polycystic Ovary Syndrome by Saccharin Sodium Using a Letrozole Rat Model

The most common cause of anovulatory infertility is polycystic ovarian syndrome (PCOS), which is closely associated with obesity metabolic and syndrome. Artificial sweetener, notably saccharin sodium (SS), has been utilized in management of obesity in PCOS. However, accumulating evidence points towards SS deleterious effects on ovarian physiology, potentially through activation of ovarian sweet and bitter taste receptors, culminating in a phenotype reminiscent of PCOS. This research embarked on exploration of SS influence on ovarian functions within a PCOS paradigm. Rats were categorized into six groups: Control, Letrozole-model, two SS groups at 2 dose levels, and two groups receiving 2 doses of SS with letrozole. The study underscored SS capability to potentiate PCOS-related anomalies. Elevated cystic profile with outer thin granulosa cells, were discernible. This owed to increased apoptotic markers cleaved CASP-3, mirrored by high BAX and low BCL-2, with p38-MAPK/ERK1/2 pathway. This manifestation was accompanied by activation of taste receptors and disruption of steroidogenic factors; StAR, CYP11A1, and 17β-HSD. Thus, SS showed an escalation in testosterone, progesterone, estrogen, and LH/FSH ratio, insinuating a perturbation in endocrine regulation. It is found that there is an impact of taste receptor downstream signaling on ovarian steroidogenesis and apoptosis instigating pathophysiological milieu of PCOS.