Myeloid differentiation protein 1 protected myocardial function against high-fat stimulation induced pathological remodelling

Overexpression of MD1 ameliorates pathological myocardial remodeling in diabetic cardiomyopathy by TLR4/STAT3 signaling pathway

Diabetic cardiomyopathy (DCM) is characterized by oxidative damage and inflammatory responses. Myeloid differentiation protein 1 (MD1) exhibits antioxidant and anti-inflammatory properties. However, the specific role of MD1 in DCM has yet to be elucidated. This study aims to investigate the role of MD1 in DCM and to elucidate the underlying mechanisms. We utilized a gain-of-function approach to explore the involvement of MD1 in DCM. Diabetes was induced in MD1-transgenic (MD1-TG) mice and their wild-type (WT) counterparts via streptozotocin (STZ) injection. Additionally, a diabetes cell model was established using H9c2 cells exposed to high glucose levels. We conducted comprehensive evaluations, including pathological analyses, echocardiography, electrocardiography, and molecular assessments, to elucidate the underlying mechanisms of MD1 in DCM. Notably, MD1 expression was reduced in the hearts of STZ-induced diabetic mice. Overexpression of MD1 significantly improved cardiac function and markedly inhibited ventricular pathological hypertrophy and fibrosis in these mice. Furthermore, MD1 overexpression resulted in a substantial decrease in myocardial reactive oxygen species (ROS) accumulation, mitigating myocardial oxidative stress and reducing the levels of inflammation-related markers such as IL-1β, IL-6, and TNF-α. Mechanistically, MD1 overexpression inhibited the activation of the TLR4/STAT3 signaling pathway, as demonstrated in both in vivo and in vitro experiments. The overexpression of MD1 significantly impeded pathological cardiac remodeling and improved cardiac function in STZ-induced diabetic mice. This effect was primarily attributed to a reduction in ROS accumulation and mitigation of myocardial oxidative stress and inflammation, facilitated by the inhibition of the TLR4/STAT3 signaling pathway.

Acetate mitigates cardiac mitochondrial dysfunction in experimental model of polycystic ovarian syndrome by modulating GPCR41/43 and PROKR1

The role of short chain fatty acid, acetate in cardiac mitochondrial dysfunction especially in PCOS individuals is unknown. Therefore, the present study investigated the modulatory role of GPCRs (41 and 43) by acetate on cardiac mitochondrial status in PCOS rat model. Eight-week-old female Wistar rats were randomly allotted into four groups (n = 5). Polycystic ovarian syndrome was induced by administering letrozole (1 mg/kg p.o.) once daily for 21 days, thereafter the animals were treated with 200 mg/kg (oral gavage) of acetate for six weeks. Letrozole-induced PCOS rats showed elevated circulating testosterone and anti-mullerian hormone, with multiple ovarian cysts. In addition, these rats also manifested insulin resistance, hyperinsulinemia, and increased plasma triglyceride (TG), TG/HDLc and decreased HDLc, as well as elevated level of cardiac TG, glycogen, glycogen synthase, and plasma/cardiac NF-kB, TNF-α, and SDF-1. Cardiac MDA and caspase-6 increased, while plasma/cardiac NrF2 decreased in PCOS animals. A decrease in mitochondrial ATP synthase, ATP/AMP ratio, CPT2 and SDH, and increased HDAC2 were observed in PCOS rats with decreased level of GPCR 41 and 43 when compared with control. Immunohistochemical evaluation of cardiac tissue also showed decrease expression of PROKR1 in PCOS rats compared with control rats. However, treatment with acetate reversed these systemic, cardiac and mitochondrial anomalies. The present results suggest the therapeutic benefit of acetate, an HDAC2i against cardiac mitochondrial dysfunction in PCOS rat model, by attenuating cardiac inflammation, oxidative stress and apoptosis and these effects are accompanied by modulation of GPCR41 and 43 as well as increased expression of PROKR1.

Palmitate-Induced Cardiac Lipotoxicity Is Relieved by the Redox-Active Motif of SELENOT through Improving Mitochondrial Function and Regulating Metabolic State

Cardiac lipotoxicity is an important contributor to cardiovascular complications during obesity. Given the fundamental role of the endoplasmic reticulum (ER)-resident Selenoprotein T (SELENOT) for cardiomyocyte differentiation and protection and for the regulation of glucose metabolism, we took advantage of a small peptide (PSELT), derived from the SELENOT redox-active motif, to uncover the mechanisms through which PSELT could protect cardiomyocytes against lipotoxicity. To this aim, we modeled cardiac lipotoxicity by exposing H9c2 cardiomyocytes to palmitate (PA). The results showed that PSELT counteracted PA-induced cell death, lactate dehydrogenase release, and the accumulation of intracellular lipid droplets, while an inert form of the peptide (I-PSELT) lacking selenocysteine was not active against PA-induced cardiomyocyte death. Mechanistically, PSELT counteracted PA-induced cytosolic and mitochondrial oxidative stress and rescued SELENOT expression that was downregulated by PA through FAT/CD36 (cluster of differentiation 36/fatty acid translocase), the main transporter of fatty acids in the heart. Immunofluorescence analysis indicated that PSELT also relieved the PA-dependent increase in CD36 expression, while in SELENOT-deficient cardiomyocytes, PA exacerbated cell death, which was not mitigated by exogenous PSELT. On the other hand, PSELT improved mitochondrial respiration during PA treatment and regulated mitochondrial biogenesis and dynamics, preventing the PA-provoked decrease in PGC1-α and increase in DRP-1 and OPA-1. These findings were corroborated by transmission electron microscopy (TEM), revealing that PSELT improved the cardiomyocyte and mitochondrial ultrastructures and restored the ER network. Spectroscopic characterization indicated that PSELT significantly attenuated infrared spectral-related macromolecular changes (i.e., content of lipids, proteins, nucleic acids, and carbohydrates) and also prevented the decrease in membrane fluidity induced by PA. Our findings further delineate the biological significance of SELENOT in cardiomyocytes and indicate the potential of its mimetic PSELT as a protective agent for counteracting cardiac lipotoxicity.

Quercetin and Its Derivative Counteract Palmitate-Dependent Lipotoxicity by Inhibiting Oxidative Stress and Inflammation in Cardiomyocytes

Cardiac lipotoxicity plays an important role in the pathogenesis of obesity-related cardiovascular disease. The flavonoid quercetin (QUE), a nutraceutical compound that is abundant in the "Mediterranean diet", has been shown to be a potential therapeutic agent in cardiac and metabolic diseases. Here, we investigated the beneficial role of QUE and its derivative Q2, which demonstrates improved bioavailability and chemical stability, in cardiac lipotoxicity. To this end, H9c2 cardiomyocytes were pre-treated with QUE or Q2 and then exposed to palmitate (PA) to recapitulate the cardiac lipotoxicity occurring in obesity. Our results showed that both QUE and Q2 significantly attenuated PA-dependent cell death, although QUE was effective at a lower concentration (50 nM) when compared with Q2 (250 nM). QUE decreased the release of lactate dehydrogenase (LDH), an important indicator of cytotoxicity, and the accumulation of intracellular lipid droplets triggered by PA. On the other hand, QUE protected cardiomyocytes from PA-induced oxidative stress by counteracting the formation of malondialdehyde (MDA) and protein carbonyl groups (which are indicators of lipid peroxidation and protein oxidation, respectively) and intracellular ROS generation, and by improving the enzymatic activities of catalase and superoxide dismutase (SOD). Pre-treatment with QUE also significantly attenuated the inflammatory response induced by PA by reducing the release of key proinflammatory cytokines (IL-1β and TNF-α). Similar to QUE, Q2 (250 nM) also significantly counteracted the PA-provoked increase in intracellular lipid droplets, LDH, and MDA, improving SOD activity and decreasing the release of IL-1β and TNF-α. These results suggest that QUE and Q2 could be considered potential therapeutics for the treatment of the cardiac lipotoxicity that occurs in obesity and metabolic diseases.

Deficiency of inhibitory TLR4 homolog RP105 exacerbates fibrosis

Activation of TLR4 by its cognate damage-associated molecular patterns (DAMPs) elicits potent profibrotic effects and myofibroblast activation in systemic sclerosis (SSc), while genetic targeting of TLR4 or its DAMPs in mice accelerates fibrosis resolution. To prevent aberrant DAMP/TLR4 activity, a variety of negative regulators evolved to dampen the magnitude and duration of the signaling. These include radioprotective 105 kDa (RP105), a transmembrane TLR4 homolog that competitively inhibits DAMP recognition of TLR4, blocking TLR4 signaling in immune cells. The role of RP105 in TLR4-dependent fibrotic responses in SSc is unknown. Using unbiased transcriptome analysis of skin biopsies, we found that levels of both TLR4 and its adaptor protein MD2 were elevated in SSc skin and significantly correlated with each other. Expression of RP105 was negatively associated with myofibroblast differentiation in SSc. Importantly, RP105-TLR4 association was reduced, whereas TLR4-TLR4 showed strong association in fibroblasts from patients with SSc, as evidenced by PLA assays. Moreover, RP105 adaptor MD1 expression was significantly reduced in SSc skin biopsies and explanted SSc skin fibroblasts. Exogenous RP105-MD1 abrogated, while loss of RP105 exaggerated, fibrotic cellular responses. Importantly, ablation of RP105 in mice was associated with augmented TLR4 signaling and aggravated skin fibrosis in complementary disease models. Thus, we believe RP105-MD1 to be a novel cell-intrinsic negative regulator of TLR4-MD2-driven sustained fibroblast activation, representing a critical regulatory network governing the fibrotic process. Impaired RP105 function in SSc might contribute to persistence of progression of the disease.

The Intriguing Role of TLR Accessory Molecules in Cardiovascular Health and Disease

Activation of Toll like receptors (TLR) plays an important role in cardiovascular disease development, progression and outcomes. Complex TLR mediated signaling affects vascular and cardiac function including tissue remodeling and repair. Being central components of both innate and adaptive arms of the immune system, TLRs interact as pattern recognition receptors with a series of exogenous ligands and endogenous molecules or so-called danger associated molecular patterns (DAMPs) that are released upon tissue injury and cellular stress. Besides immune cells, a number of structural cells within the cardiovascular system, including endothelial cells, smooth muscle cells, fibroblasts and cardiac myocytes express TLRs and are able to release or sense DAMPs. Local activation of TLR-mediated signaling cascade induces cardiovascular tissue repair but in a presence of constant stimuli can overshoot and cause chronic inflammation and tissue damage. TLR accessory molecules are essential in guiding and dampening these responses toward an adequate reaction. Furthermore, accessory molecules assure specific and exclusive TLR-mediated signal transduction for distinct cells and pathways involved in the pathogenesis of cardiovascular diseases. Although much has been learned about TLRs activation in cardiovascular remodeling, the exact role of TLR accessory molecules is not entirely understood. Deeper understanding of the role of TLR accessory molecules in cardiovascular system may open therapeutic avenues aiming at manipulation of inflammatory response in cardiovascular disease. The present review outlines accessory molecules for membrane TLRs that are involved in cardiovascular disease progression. We first summarize the up-to-date knowledge on TLR signaling focusing on membrane TLRs and their ligands that play a key role in cardiovascular system. We then survey the current evidence of the contribution of TLRs accessory molecules in vascular and cardiac remodeling including myocardial infarction, heart failure, stroke, atherosclerosis, vein graft disease and arterio-venous fistula failure.

The Potential Role of RP105 in Regulation of Inflammation and Osteoclastogenesis During Inflammatory Diseases

Inflammatory diseases have a negative impact on bone homeostasis via exacerbated local and systemic inflammation. Bone resorbing osteoclasts are mainly derived from hematopoietic precursors and bone marrow monocytes. Induced osteoclastogenesis during inflammation, autoimmunity, metabolic diseases, and cancers is associated with bone loss and osteoporosis. Proinflammatory cytokines, pathogen-associated molecular patterns, or endogenous pathogenic factors induce osteoclastogenic differentiation by binding to the Toll-like receptor (TLR) family expressed on surface of osteoclast precursors. As a non-canonical member of the TLRs, radioprotective 105 kDa (RP105 or CD180) and its ligand, myeloid differentiation protein 1 (MD1), are involved in several bone metabolic disorders. Reports from literature had demonstrated RP105 as an important activator of B cells, bone marrow monocytes, and macrophages, which regulates inflammatory cytokines release from immune cells. Reports from literature had shown the association between RP105 and other TLRs, and the downstream signaling mechanisms of RP105 with different “signaling-competent” partners in immune cells during different disease conditions. This review is focused to summarize: (1) the role of RP105 on immune cells’ function and inflammation regulation (2) the potential regulatory roles of RP105 in different disease-mediated osteoclast activation and the underlying mechanisms, and (3) the different “signaling-competent” partners of RP105 that regulates osteoclastogenesis.

Piperine protects against pyroptosis in myocardial ischaemia/reperfusion injury by regulating the miR-383/RP105/AKT signalling pathway

miRNA-mediated pyroptosis play crucial effects in the development of myocardial ischaemia/reperfusion (I/R) injury (MIRI). Piperine (PIP) possesses multiple pharmacological effects especially in I/R condition. This study focuses on whether PIP protects MIRI from pyroptosis via miR-383-dependent pathway. Rat MIRI model was established by 30 minutes of LAD ligation and 4 hours of reperfusion. Myocardial enzymes, histomorphology, structure and function were detected to evaluate MIRI. Recombinant adenoviral vectors for miR-383 overexpression or miR-383 silencing or RP105 knockdown were constructed, respectively. Luciferase reporter analysis was used to confirm RP105 as a target of miR-383. Pyroptosis-related markers were measured by Western blotting assay. The results showed that I/R provoked myocardial injury, as shown by the increases of LDH/CK releases, infarcted areas and apoptosis as well as worsened function and structure. Pyroptosis-related mediators including NLRP3, cleaved caspase-1, cleaved IL-1β and IL-18 were also reinforced after MIRI. However, PIP treatment greatly ameliorated MIRI in parallel with pyroptotic repression. In mechanistic studies, MIRI-caused elevation of miR-383 and decrease of RP105/PI3K/AKT pathway were reverted by PIP treatment. Luciferase reporter assay confirmed RP105 as a miR-383 target. miR-383 knockdown ameliorated but miR-383 overexpression facilitated pyroptosis and MIRI. Moreover, the anti-pyroptotic effect from miR-383 silencing was verified to be relied on the RP105/PI3K/AKT signalling pathway. Additionally, our present study further indicated the miR-383/RP105/AKT-dependent approach resulting from PIP administration against pyroptosis in MIRI. Therefore, PIP treatment attenuates MIRI and pyroptosis by regulating miR-383/RP105/AKT pathway, and it may provide a therapeutic manner for the treatment of MIRI.

MD1 Depletion Predisposes to Ventricular Arrhythmias in the Setting of Myocardial Infarction

BACKGROUND

Myeloid differentiation protein 1 (MD1) is expressed in the human heart and is a negative regulator of Toll-like receptor 4 (TLR4) signalling. MD1 exerts anti-arrhythmic effects.

AIM

The aim of this study was to determine the role of MD1 in myocardial infarction (MI)-related ventricular arrhythmias (VAs).

METHOD

Myocardial infarction was induced by surgical ligation of the left anterior coronary artery in MD1 knockout (KO) mice and their wild-type littermates. Myocardial infarction-induced vulnerability to VAs and its underlying mechanisms were evaluated.

RESULTS

Myeloid differentiation protein 1 was downregulated in the MI mice. Myeloid differentiation protein 1 deficiency decreased post-MI left ventricular (LV) function and increased the infarct size. The MI mice exhibited prolonged action potential duration (APD), enhanced APD alternans thresholds, and a higher incidence of VAs. Myocardial infarction-induced LV fibrosis and inflammation decreased the expression levels of Kv4.2, Kv4.3, Kv1.5, and Kv2.1, increased Cav1.2 expression, and disturbed Ca²⁺ handling protein expression. These MI-induced adverse effects were further exacerbated in KO mice. Mechanistically, MD1 deletion markedly enhanced the activation of the TLR4/calmodulin-dependent protein kinase II (CaMKII) signalling pathway in post-MI mice.

CONCLUSIONS

Myeloid differentiation protein 1 deletion increases the vulnerability to VAs in post-MI mice. This is mainly caused by the aggravated maladaptive LV fibrosis and inflammation and interference with the expressions of ion channels and Ca²⁺ handling proteins, which is related to enhanced activation of the TLR4/CaMKII signalling pathway.

Key Player in Cardiac Hypertrophy, Emphasizing the Role of Toll-Like Receptor 4

Toll-like receptor 4 (TLR4), a key pattern recognition receptor, initiates the innate immune response and leads to chronic and acute inflammation. In the past decades, accumulating evidence has implicated TLR4-mediated inflammatory response in regulation of myocardium hypertrophic remodeling, indicating that regulation of the TLR4 signaling pathway may be an effective strategy for managing cardiac hypertrophy's pathophysiology. Given TLR4's significance, it is imperative to review the molecular mechanisms and roles underlying TLR4 signaling in cardiac hypertrophy. Here, we comprehensively review the current knowledge of TLR4-mediated inflammatory response and its interaction ligands and co-receptors, as well as activation of various intracellular signaling. We also describe the associated roles in promoting immune cell infiltration and inflammatory mediator secretion, that ultimately cause cardiac hypertrophy. Finally, we provide examples of some of the most promising drugs and new technologies that have the potential to attenuate TLR4-mediated inflammatory response and prevent or reverse the ominous cardiac hypertrophy outcomes.

The Crosstalk between Cardiac Lipotoxicity and Mitochondrial Oxidative Stress in the Cardiac Alterations in Diet-Induced Obesity in Rats

The impact of the mitochondria-targeted antioxidant MitoQ was evaluated in the cardiac alterations associated with obesity. Male Wistar rats were fed either a high fat diet (HFD, 35% fat) or a standard diet (CT, 3.5% fat) for 7 weeks and treated with MitoQ (200 µM). The effect of MitoQ (5 nM) in rat cardiac myoblasts treated for 24 h with palmitic acid (PA, 200 µM) was evaluated. MitoQ reduced cardiac oxidative stress and prevented the development of cardiac fibrosis, hypertrophy, myocardial ¹⁸-FDG uptake reduction, and mitochondrial lipid remodeling in HFD rats. It also ameliorated cardiac mitochondrial protein level changes observed in HFD: reductions in fumarate hydratase, complex I and II, as well as increases in mitofusin 1 (MFN1), peroxisome proliferator-activated receptor gamma coactivator 1-alpha, and cyclophilin F (cycloF). In vitro, MitoQ prevented oxidative stress and ameliorated alterations in mitochondrial proteins observed in palmitic acid (PA)-stimulated cardiac myoblasts: increases in carnitine palmitoyltransferase 1A, cycloF, and cytochrome C. PA induced phosphorylation of extracellular signal-regulated kinases and nuclear factor-κB p65. Therefore, the data show the beneficial effects of MitoQ in the cardiac damage induced by obesity and suggests a crosstalk between lipotoxicity and mitochondrial oxidative stress in this damage

The effect of MD1 on potassium and L-type calcium current of cardiomyocytes from high-fat diet mice

Myeloid differentiation protein 1 (MD1) is exerted an anti-arrhythmic effect in obese mice. Therefore, we sought to clarify whether MD1 can alter the electrophysiological remodeling of cardiac myocytes from obese mice by regulating voltage-gated potassium current and calcium current. MD1 knock-out (KO) and wild type (WT) mice were given a high-fat diet (HFD) for 20 weeks, starting at the age of 6 weeks. The potential electrophysiological mechanisms were estimated by whole-cell patch-clamp and molecular analysis. After 20-week HFD feeding, action potential duration (APD) from left ventricular myocytes of MD1-KO mice revealed APD₂₀, APD₅₀, and APD₉₀ were profoundly enlarged. Furthermore, HFD mice showed a decrease in the fast transient outward potassium currents (I_to,f), slowly inactivating potassium current (I_{K, slow}), and inward rectifier potassium current (I_K1). Besides, HFD-fed mice showed that the current density of I_CaL was significantly lower, and the haft inactivation voltage was markedly shifted right. These HFD induced above adverse effects were further exacerbated in KO mice. The mRNA expression of potassium ion channels (Kv4.2, Kv4.3, Kv2.1, Kv1.5, and Kir2.1) and calcium ion channel (Cav1.2) was markedly decreased in MD1-KO HFD-fed mice. MD1 deletion led to down-regulated potassium currents and slowed inactivation of L-type calcium channel in an obese mice model.

MD-1 Deficiency Accelerates Myocardial Inflammation and Apoptosis in Doxorubicin-Induced Cardiotoxicity by Activating the TLR4/MAPKs/Nuclear Factor kappa B (NF-κB) Signaling Pathway

Background

Myocardial apoptosis and inflammation play important roles in doxorubicin (DOX)-caused cardiotoxicity. Our prior studies have characterized the effects of myeloid differentiation protein 1(MD-1) in pathological cardiac remodeling and myocardial ischemia/reperfusion (I/R) injury, but its participations and potential molecular mechanisms in DOX-caused cardiotoxicity remain unknown.

Material/Methods

In the present study, MD-1 knockout mice were generated, and a single intraperitoneal injection of DOX (15 mg/kg) was performed to elicit DOX-induced cardiotoxicity. Cardiac function, histological change, mitochondrial structure, myocardial death, apoptosis, inflammation, and molecular alterations were measured systemically.

Results

The results showed that the protein and mRNA levels of MD-1 were dramatically downregulated in DOX-treated cardiomyocytes. DOX insult markedly accelerated cardiac dysfunction and injury, followed by enhancements of apoptosis and inflammation, all of which were further aggravated in MD-1 knockout mice. Mechanistically, the TLR4/MAPKs/NF-κB pathways, which were over-activated in MD-1-deficient mice, were significantly increased in DOX-damaged cardiomyocytes. Moreover, the abolishment of TLR4 or NF-κB via a specific inhibitor exerted protective effects against the adverse effects of MD-1 loss on DOX-caused cardiotoxicity.

Conclusions

Collectively, these findings suggest that MD-1 is a novel target for the treatment of DOX-induced cardiotoxicity.

Myeloid differentiation protein 1 protected myocardial function against high-fat stimulation induced pathological remodelling

Myeloid differentiation 1 (MD‐1) is a secreted protein that regulates the immune response of B cell through interacting with radioprotective 105 (RP105). Disrupted immune response may contribute to the development of cardiac diseases, while the roles of MD‐1 remain elusive. Our studies aimed to explore the functions and molecular mechanisms of MD‐1 in obesity‐induced cardiomyopathy. H9C2 myocardial cells were treated with free fatty acid (FFA) containing palmitic acid and oleic acid to challenge high‐fat stimulation and adenoviruses harbouring human MD‐1 coding sequences or shRNA for MD‐1 overexpression or knockdown in vitro. MD‐1 overexpression or knockdown transgenic mice were generated to assess the effects of MD‐1 on high‐fat diet (HD) induced cardiomyopathy in vivo. Our results showed that MD‐1 was down‐regulated in H9C2 cells exposed to FFA stimulation for 48 hours and in obesity mice induced by HD for 20 weeks. Both in vivo and in vitro, silencing of MD‐1 accelerated myocardial function injury induced by HD stimulation through increased cardiac hypertrophy and fibrosis, while overexpression of MD‐1 alleviated the effects of HD by inhibiting the process of cardiac remodelling. Moreover, the MAPK and NF‐κB pathways were overactivated in MD‐1 deficient mice and H9C2 cells after high‐fat treatment. Inhibition of MAPK and NF‐κB pathways played a cardioprotective role against the adverse effects of MD‐1 silencing on high‐fat stimulation induced pathological remodelling. In conclusion, MD‐1 protected myocardial function against high‐fat stimulation induced cardiac pathological remodelling through negative regulation for MAPK/NF‐κB signalling pathways, providing feasible strategies for obesity cardiomyopathy.