Arsenic Promotes NF-Κb-Mediated Fibroblast Dysfunction and Matrix Remodeling to Impair Muscle Stem Cell Function

Oleanolic acid inhibits hypoxic tumor-derived exosomes-induced premetastatic niche formation in hepatocellular carcinoma by targeting ERK1/2-NFκB signaling

BACKGROUND

Pulmonary premetastatic niche (PMN) formation plays a key role in the lung metastasis of hepatocellular carcinoma (HCC). Hypoxia promotes the secretion of tumor-derived exosomes (TDEs) and facilitates the formation of PMN. However, the mechanisms remain unexplored.

METHODS

TDEs from normoxic (N-TDEs) or hypoxic (H-TDEs) HCC cells were used to induce fibroblast activation in vitro and PMN formation in vivo. Oleanolic acid (OA) was intragastrically administered to TDEs-preconditioned mice. Bioinformatics analysis and drug affinity responsive target stability (DARTS) assays were performed to identify targets of OA in fibroblasts.

RESULTS

H-TDEs induced activation of pulmonary fibroblasts, promoted formation of pulmonary PMN and subsequently facilitated lung metastasis of HCC. OA inhibited TDEs-induced PMN formation and lung metastasis and suppressed TDEs-mediated fibroblast activation. MAPK1 and MAPK3 (ERK1/2) were the potential targets of OA. Furthermore, H-TDEs enhanced ERK1/2 phosphorylation in fibroblasts in vitro and in vivo, which was suppressed by OA treatment. Blocking ERK1/2 signaling with its inhibitor abated H-TDEs-induced activation of fibroblasts and PMN formation. H-TDEs-induced phosphorylation of ERK1/2 in fibroblasts touched off the activation NF-κB p65, which was mitigated by OA. In addition, the ERK activator C16-PAF recovered the activation of ERK1/2 and NF-κB p65 in H-TDEs-stimulated MRC5 cells upon OA treatment.

CONCLUSION

The present study offers insights into the prevention of TDEs-induced PMN, which has been insufficiently investigated. OA suppresses the activation of inflammatory fibroblasts and the development of pulmonary PMN by targeting ERK1/2 and thereby has therapeutic potential in the prevention of lung metastasis of HCC.

Chronic arsenite exposure induced skeletal muscle atrophy by disrupting angiotensin II-melatonin axis in rats

Arsenic is a well-known environmental toxicant and emerging evidence suggests that arsenic exposure has potential skeletal muscle toxicity; however, the underlying mechanism has not yet been clarified. The aim of this study was to investigate the correlation among adverse effects of subchronic and chronic environmental arsenic exposure on skeletal muscle as well as specific myokines secretion and angiotensin II (AngII)-melatonin (MT) axis in rats. Four-week-old rats were exposed to arsenite (iAs) in drinking water at environmental relevant concentration of 10 ppm for 3 or 9 months. Results indicated that the gastrocnemius muscle had atrophied and its mass was decreased in rats exposed to arsenite for 9 months, whereas, they had no significant changes in rats exposed to arsenite for 3 months. The levels of serum-specific myokine irisin and gastrocnemius muscle insulin-like growth factor-1 (IGF-1) were increased in 3-month exposure group and decreased in 9-month exposure group, while serum myostatin (MSTN) was increased significantly in 9-month exposure group. In addition, serum AngII level increased both in 3- and 9-month exposure groups, while serum MT level increased in 3-month exposure group and decreased in 9-month exposure group. Importantly, the ratio of AngII to MT level in serum increased gradually with the prolongation of arsenite exposure. It showed a certain correlation between AngII-MT axis and gastrocnemius muscle mass, gastrocnemius muscle level of IGF-1 or serum levels of irisin and MSTN. In conclusion, the disruption of AngII-MT axis balance may be a significant factor for skeletal muscle atrophy induced by chronic environmental arsenic exposure.

Arsenic and adipose tissue: an unexplored pathway for toxicity and metabolic dysfunction

Arsenic-contaminated drinking water can induce various disorders by disrupting lipid and glucose metabolism in adipose tissue, leading to insulin resistance. It inhibits adipocyte development and exacerbates insulin resistance, though the precise impact on lipid synthesis and lipolysis remains unclear. This review aims to explore the processes and pathways involved in adipogenesis and lipolysis within adipose tissue concerning arsenic-induced diabetes. Although arsenic exposure is linked to type 2 diabetes, the specific role of adipose tissue in its pathogenesis remains uncertain. The review delves into arsenic's effects on adipose tissue and related signaling pathways, such as SIRT3-FOXO3a, Ras-MAP-AP-1, PI(3)-K-Akt, endoplasmic reticulum stress proteins, CHOP10, and GPCR pathways, emphasizing the role of adipokines. This analysis relies on existing literature, striving to offer a comprehensive understanding of different adipokine categories contributing to arsenic-induced diabetes. The findings reveal that arsenic detrimentally impacts white adipose tissue (WAT) by reducing adipogenesis and promoting lipolysis. Epidemiological studies have hinted at a potential link between arsenic exposure and obesity development, with limited research suggesting a connection to lipodystrophy. Further investigations are needed to elucidate the mechanistic association between arsenic exposure and impaired adipose tissue function, ultimately leading to insulin resistance.

Matrix-bound nanovesicle-associated IL-33 supports functional recovery after skeletal muscle injury by initiating a pro-regenerative macrophage phenotypic transition

Injuries to skeletal muscle are among the most common injuries in civilian and military populations, accounting for nearly 60% of extremity injuries. The standard of care for severe extremity injury has been focused upon limb salvage procedures and the utilization of tissue grafts or orthotics in conjunction with rehabilitation to avoid amputation. Nonetheless, many patients have persistent strength and functional deficits that permanently impact their quality of life. Preclinical and clinical studies have shown that partial restoration of functional skeletal muscle tissue following injury can be achieved by the implantation of a biologic scaffold composed of extracellular matrix (ECM). These favorable outcomes are mediated, at least in part, through local immunomodulation. The mechanisms underlying this immunomodulatory effect, however, are poorly understood. The present study investigates a potential mechanistic driver of the immunomodulatory effects; specifically, the effect of selected ECM components upon inflammation resolution and repair. Results show that the host response to skeletal muscle injury is profoundly altered and functional recovery decreased in il33-/- mice compared to age- and sex-matched wildtype counterparts by 14 days post-injury. Results also show that IL-33, contained within matrix-bound nanovesicles (MBV), supports skeletal muscle regeneration by regulating local macrophage activation toward a pro-remodeling phenotype via canonical and non-canonical pathways to improve functional recovery from injury compared to untreated il33-/- counterparts. Taken together, these data suggest that MBV and their associated IL-33 cargo represent a novel homeostatic signaling mechanism that contributes to skeletal muscle repair.

Arsenic disrupts extracellular vesicle-mediated signaling in regenerating myofibers

Chronic exposure to environmental arsenic is a public health crisis affecting hundreds of millions of individuals worldwide. Though arsenic is known to contribute to many pathologies and diseases, including cancers, cardiovascular and pulmonary diseases, and neurological impairment, the mechanisms for arsenic-promoted disease remain unresolved. This is especially true for arsenic impacts on skeletal muscle function and metabolism, despite the crucial role that skeletal muscle health plays in maintaining cardiovascular health, systemic homeostasis, and cognition. A barrier to researching this area is the challenge of interrogating muscle cell-specific effects in biologically relevant models. Ex vivo studies investigating mechanisms for muscle-specific responses to arsenic or other environmental contaminants primarily utilize traditional 2-dimensional culture models that cannot elucidate effects on muscle physiology or function. Therefore, we developed a contractile 3-dimensional muscle construct model-composed of primary mouse muscle progenitor cells differentiated in a hydrogel matrix-to study arsenic exposure impacts on skeletal muscle regeneration. Muscle constructs exposed to low-dose (50 nM) arsenic exhibited reduced strength and myofiber diameter following recovery from muscle injury. These effects were attributable to dysfunctional paracrine signaling mediated by extracellular vesicles (EVs) released from muscle cells. Specifically, we found that EVs collected from arsenic-exposed muscle constructs recapitulated the inhibitory effects of direct arsenic exposure on myofiber regeneration. In addition, muscle constructs treated with EVs isolated from muscles of arsenic-exposed mice displayed significantly decreased strength. Our findings highlight a novel model for muscle toxicity research and uncover a mechanism of arsenic-induced muscle dysfunction by the disruption of EV-mediated intercellular communication.

Neuromuscular electrical stimulation enhances the ability of serum extracellular vesicles to regenerate aged skeletal muscle after injury

Exercise promotes healthy aging of skeletal muscle. This benefit may be mediated by youthful factors in the circulation released in response to an exercise protocol. While numerous studies to date have explored soluble proteins as systemic mediators of rejuvenating effect of exercise on tissue function, here we showed that the beneficial effect of skeletal muscle contractile activity on aged muscle function is mediated, at least in part, by regenerative properties of circulating extracellular vesicles (EVs). Muscle contractile activity elicited by neuromuscular electrical stimulation (NMES) decreased intensity of expression of the tetraspanin surface marker, CD63, on circulating EVs. Moreover, NMES shifted the biochemical Raman fingerprint of circulating EVs in aged animals with significant changes in lipid and sugar content in response to NMES when compared to controls. As a demonstration of the physiological relevance of these EV changes, we showed that intramuscular administration of EVs derived from aged animals subjected to NMES enhanced aged skeletal muscle healing after injury. These studies suggest that repetitive muscle contractile activity enhances the regenerative properties of circulating EVs in aged animals.

Engineering Bioactive M2 Macrophage-Polarized, Anti-inflammatory, miRNA-Based Liposomes for Functional Muscle Repair: From Exosomal Mechanisms to Biomaterials

Severe inflammation and myogenic differentiation disorder are the major obstacles to skeletal muscle healing after injury. MicroRNAs (miRNAs) play an important role as regulatory molecules during the process of muscle healing, but the detailed mechanism of miRNA-mediated intercellular communication between myoblasts and macrophages remains unclear. Here, it is reported that myoblasts secrete miRNAs-enriched exosomes in the inflammatory environment, through which miR-224 is transferred into macrophages to inhibit M2 polarization. Further data demonstrate that WNT-9a may be a direct target of miR-224 for macrophage polarization. In turn, the secretome of M1 macrophages impairs myogenic differentiation and promotes proliferation. Single-cell integration analysis suggests that the elevation of exosome-derived miR-224 is caused by the activation of the key factor E2F1 in myoblasts and demonstrates the RB/E2F1/miR-224/WNT-9a axis. In vivo results show that treatment with antagomir-224 or liposomes containing miR-224 inhibitors suppresses fibrosis and improves muscle recovery. These findings indicate the importance of the crosstalk between myoblasts and macrophages via miRNA-containing exosomes in the regulation of macrophage polarization and myogenic differentiation/proliferation during muscle healing. This study provides a strategy for treating muscle injury through designing an M2 polarization-enabling anti-inflammatory and miRNA-based bioactive material.

Arsenic Exposure through Dietary Intake and Associated Health Hazards in the Middle East

Dietary arsenic (As) contamination is a major public health issue. In the Middle East, the food supply relies primarily on the import of food commodities. Among different age groups the main source of As exposure is grains and grain-based food products, particularly rice and rice-based dietary products. Rice and rice products are a rich source of core macronutrients and act as a chief energy source across the world. The rate of rice consumption ranges from 250 to 650 g per day per person in South East Asian countries. The source of carbohydrates through rice is one of the leading causes of human As exposure. The Gulf population consumes primarily rice and ready-to-eat cereals as a large proportion of their meals. Exposure to arsenic leads to an increased risk of non-communicable diseases such as dysbiosis, obesity, metabolic syndrome, diabetes, chronic kidney disease, chronic heart disease, cancer, and maternal and fetal complications. The impact of arsenic-containing food items and their exposure on health outcomes are different among different age groups. In the Middle East countries, neurological deficit disorder (NDD) and autism spectrum disorder (ASD) cases are alarming issues. Arsenic exposure might be a causative factor that should be assessed by screening the population and regulatory bodies rechecking the limits of As among all age groups. Our goals for this review are to outline the source and distribution of arsenic in various foods and water and summarize the health complications linked with arsenic toxicity along with identified modifiers that add heterogeneity in biological responses and suggest improvements for multi-disciplinary interventions to minimize the global influence of arsenic. The development and validation of diverse analytical techniques to evaluate the toxic levels of different As contaminants in our food products is the need of the hour. Furthermore, standard parameters and guidelines for As-containing foods should be developed and implemented.

Arsenic Exposure Impairs Intestinal Stromal Cells

Arsenic is a toxicant commonly found in drinking water. Even though its main route of exposure is oral, little is known of the impact of in vivo arsenic exposure on small intestine. In vitro studies have shown that arsenic decreases differentiation of stem and progenitor cells in several different tissues. Thus, small intestinal organoids were used to assess if arsenic exposure would also impair intestinal stem cell differentiation. Unexpectedly, no changes in markers of differentiated epithelial cells were seen. However, exposing mice to 100 ppb arsenic in drinking water for 5 weeks impaired distinct populations of intestinal stromal cells. Arsenic reduced the width of the pericryptal lamina propria by 1.6-fold, and reduced Pdgfra mRNA expression, which is expressed in intestinal telocytes and trophocytes, by 4.2-fold. The height or extension of Pdgfra⁺ telopodes into the villus tip was also significantly reduced. Transcript expression of several other stromal cell markers, such as Grem1, Gli, CD81, were reduced by 1.9-, 2.3-, and 1.4-fold, respectively. Further, significant correlations exist between levels of Pdgfra and Gli1, Grem1, and Bmp4. Our results suggest arsenic impairs intestinal trophocytes and telocytes, leading to alterations in the Bmp signaling pathway.

Arsenic Toxicity on Metabolism and Autophagy in Adipose and Muscle Tissues

Arsenic, a naturally occurring metalloid derived from the environment, has been studied worldwide for its causative effects in various cancers. However, the effects of arsenic toxicity on the development and progression of metabolic syndrome, including obesity and diabetes, has received less attention. Many studies suggest that metabolic dysfunction and autophagy dysregulation of adipose and muscle tissues are closely related to the development of metabolic disease. In the USA, arsenic contamination has been reported in some ground water, soil and grain samples in major agricultural regions, but the effects on adipose and muscle tissue metabolism and autophagy have not been investigated much. Here, we highlight arsenic toxicity according to the species, dose and exposure time and the effects on adipose and muscle tissue metabolism and autophagy. Historically, arsenic was used as both a poison and medicine, depending on the dose and treatment time. In the modern era, arsenic intoxication has significantly increased due to exposure from water, soil and food, which could be a contributing factor in the development and progression of metabolic disease. From this review, a better understanding of the pathogenic mechanisms by which arsenic alters metabolism and autophagy regulation could become a cornerstone leading to the development of therapeutic strategies against arsenic-induced toxicity and metabolic disease.

Regulation of aged skeletal muscle regeneration by circulating extracellular vesicles

Heterochronic blood exchange (HBE) has demonstrated that circulating factors restore youthful features to aged tissues. However, the systemic mediators of those rejuvenating effects remain poorly defined. We show here that the beneficial effect of young blood on aged muscle regeneration was diminished when serum was depleted of extracellular vesicles (EVs). Whereas EVs from young animals rejuvenate aged cell bioenergetics and skeletal muscle regeneration, aging shifts EV subpopulation heterogeneity and compromises downstream benefits on recipient cells. Machine learning classifiers revealed that aging shifts the nucleic acid, but not protein, fingerprint of circulating EVs. Alterations in sub-population heterogeneity were accompanied by declines in transcript levels of the pro-longevity protein, α-Klotho, and injection of EVs improved muscle regeneration in a Klotho mRNA-dependent manner. These studies demonstrate that EVs play a key role in the rejuvenating effects of HBE and that Klotho transcripts within EVs phenocopy the effects of young serum on aged skeletal muscle.

Exosomes derived from inflammatory myoblasts promote M1 polarization and break the balance of myoblast proliferation/differentiation

BACKGROUND

Acute muscle injuries are one of the most common injuries in sports. Severely injured muscles are prone to re-injury due to fibrotic scar formation caused by prolonged inflammation. How to regulate inflammation and suppress fibrosis is the focus of promoting muscle healing. Recent studies have found that myoblasts and macrophages play important roles in the inflammatory phase following muscle injury; however, the crosstalk between these two types of cells in the inflammatory environment, particularly the exosome-related mechanisms, had not been well studied.

AIM

To evaluate the effects of exosomes from inflammatory C2C12 myoblasts (IF-C2C12-Exos) on macrophage polarization and myoblast proliferation/differentiation.

METHODS

A model of inflammation was established in vitro by lipopolysaccharide stimulation of myoblasts. C2C12-Exos were isolated and purified from the supernatant of myoblasts by gradient centrifugation. Multiple methods were used to identify the exosomes. Gradient concentrations of IF-C2C12-Exos were added to normal macrophages and myoblasts. PKH67 fluorescence tracing was used to identify the interaction between exosomes and cells. Microscopic morphology, Giemsa stain, and immunofluorescence were carried out for histological analysis. Additionally, ELISA assays, flow cytometry, and western blot were conducted to analyze molecular changes. Moreover, myogenic proliferation was assessed by the BrdU test, scratch assay, and CCK-8 assay.

RESULTS

We found that the PKH-67-marked C2C12-Exos can be endocytosed by both macrophages and myoblasts. IF-C2C12-Exos induced M1 macrophage polarization and suppressed the M2 phenotype in vitro. In addition, these exosomes also stimulated the inflammatory reactions of macrophages. Furthermore, we demonstrated that IF-C2C12-Exos disrupted the balance of myoblast proliferation/differentiation, leading to enhanced proliferation and suppressed fibrogenic/myogenic differentiation.

CONCLUSION

IF-C2C12-Exos can induce M1 polarization, resulting in a sustained and aggravated inflammatory environment that impairs myoblast differentiation, and leads to enhanced myogenic proliferation. These results demonstrate why prolonged inflammation occurs after acute muscle injury and provide a new target for the regulation of muscle regeneration.

Arsenic Secondary Methylation Capacity Is Inversely Associated with Arsenic Exposure-Related Muscle Mass Reduction

Skeletal muscle mass reduction has been implicated in insulin resistance (IR) that promotes cardiometabolic diseases. We have previously reported that arsenic exposure increases IR concomitantly with the reduction of skeletal muscle mass among individuals exposed to arsenic. The arsenic methylation capacity is linked to the susceptibility to some arsenic exposure-related diseases. However, it remains unknown whether the arsenic methylation capacity affects the arsenic-induced reduction of muscle mass and elevation of IR. Therefore, this study examined the associations between the arsenic methylation status and skeletal muscle mass measures with regard to IR by recruiting 437 participants from low- and high-arsenic exposure areas in Bangladesh. The subjects' skeletal muscle mass was estimated by their lean body mass (LBM) and serum creatinine levels. Subjects' drinking water arsenic concentrations were positively associated with total urinary arsenic concentrations and the percentages of MMA, as well as inversely associated with the percentages of DMA and the secondary methylation index (SMI). Subjects' LBM and serum creatinine levels were positively associated with the percentage of DMA and SMI, as well as inversely associated with the percentage of MMA. HOMA-IR showed an inverse association with SMI, with a confounding effect of sex. Our results suggest that reduced secondary methylation capacity is involved in the arsenic-induced skeletal muscle loss that may be implicated in arsenic-induced IR and cardiometabolic diseases.

Arsenic Directs Stem Cell Fate by Imparting Notch Signaling Into the Extracellular Matrix Niche

Compromise of skeletal muscle metabolism and composition may underlie the etiology of cardiovascular and metabolic disease risk from environmental arsenic exposures. We reported that arsenic impairs muscle maintenance and regeneration by inducing maladaptive mitochondrial phenotypes in muscle stem cells (MuSC), connective tissue fibroblasts (CTF), and myofibers. We also found that arsenic imparts a dysfunctional memory in the extracellular matrix (ECM) that disrupts the MuSC niche and is sufficient to favor the expansion and differentiation of fibrogenic MuSC subpopulations. To investigate the signaling mechanisms involved in imparting a dysfunctional ECM, we isolated skeletal muscle tissue and CTF from mice exposed to 0 or 100 μg/l arsenic in their drinking water for 5 weeks. ECM elaborated by arsenic-exposed CTF decreased myogenesis and increased fibrogenic/adipogenic MuSC subpopulations and differentiation. However, treating arsenic-exposed mice with SS-31, a mitochondrially targeted peptide that repairs the respiratory chain, reversed the arsenic-promoted CTF phenotype to one that elaborated an ECM supporting normal myogenic differentiation. SS-31 treatment also reversed arsenic-induced Notch1 expression, resulting in an improved muscle regeneration after injury. We found that persistent arsenic-induced CTF Notch1 expression caused the elaboration of dysfunctional ECM with increased expression of the Notch ligand DLL4. This DLL4 in the ECM was responsible for misdirecting MuSC myogenic differentiation. These data indicate that arsenic impairs muscle maintenance and regenerative capacity by targeting CTF mitochondria and mitochondrially directed expression of dysfunctional regulators in the stem cell niche. Therapies that restore muscle cell mitochondria may effectively treat arsenic-induced skeletal muscle dysfunction and compositional decline.

Arsenic Stimulates Myoblast Mitochondrial Epidermal Growth Factor Receptor to Impair Myogenesis

Arsenic exposure impairs muscle metabolism, maintenance, progenitor cell differentiation, and regeneration following acute injury. Low to moderate arsenic exposures target muscle fiber and progenitor cell mitochondria to epigenetically decrease muscle quality and regeneration. However, the mechanisms for how low levels of arsenic signal for prolonged mitochondrial dysfunction are not known. In this study, arsenic attenuated murine C2C12 myoblasts differentiation and resulted in abnormal undifferentiated myoblast proliferation. Arsenic prolonged ligand-independent phosphorylation of mitochondrially localized epidermal growth factor receptor (EGFR), a major driver of proliferation. Treating cells with a selective EGFR kinase inhibitor, AG-1478, prevented arsenic inhibition of myoblast differentiation. AG-1478 decreased arsenic-induced colocalization of pY845EGFR with mitochondrial cytochrome C oxidase subunit II, as well as arsenic-enhanced mitochondrial membrane potential, reactive oxygen species generation, and cell cycling. All of the arsenic effects on mitochondrial signaling and cell fate were mitigated or reversed by addition of mitochondrially targeted agents that restored mitochondrial integrity and function. Thus, arsenic-driven pathogenesis in skeletal muscle requires sustained mitochondrial EGFR activation that promotes progenitor cell cycling and proliferation at the detriment of proper differentiation. Collectively, these findings suggest that the arsenic-activated mitochondrial EGFR pathway drives pathogenic signaling for impaired myoblast metabolism and function.

Non-redox cycling mechanisms of oxidative stress induced by PM metals

Metallic compounds contribute to the oxidative stress of ambient particulate matter (PM) exposure. The toxicity of redox inert ions of cadmium, mercury, lead and zinc, as well as redox-active ions of vanadium and chromium is underlain by dysregulation of mitochondrial function and loss of signaling quiescence. Central to the initiation of these effects is the interaction of metal ions with cysteinyl thiols on glutathione and key regulatory proteins, which leads to impaired mitochondrial electron transport and persistent pan-activation of signal transduction pathways. The mitochondrial and signaling effects are linked by the production of H₂O₂, generated from mitochondrial superoxide anion or through the activation of NADPH oxidase, which extends the range and amplifies the magnitude of the oxidative effects of the metals. This oxidative burden can be further potentiated by inhibitory effects of the metals on the enzymes of the glutathione and thioredoxin systems. Along with the better-known Fenton-based mechanisms, the non-redox cycling mechanisms of oxidative stress induced by metals constitute significant pathways for cellular injury induced by PM inhalation.

Rice Intake, Arsenic Exposure, and Subclinical Cardiovascular Disease Among US Adults in MESA

Background Arsenic-related cardiovascular effects at exposure levels below the US Environmental Protection Agency's standard of 10 μg/L are unclear. For these populations, food, especially rice, is a major source of exposure. We investigated associations of rice intake, a marker of arsenic exposure, with subclinical cardiovascular disease (CVD) markers in a multiethnic population. Methods and Results Between 2000 and 2002, MESA (Multi-Ethnic Study of Atherosclerosis) enrolled 6814 adults without clinical CVD. We included 5050 participants with baseline data on rice intake and markers of 3 CVD domains: inflammation (hsCRP [high-sensitivity C-reactive protein], interleukin-6, and fibrinogen), vascular function (aortic distensibility, carotid distensibility, and brachial flow-mediated dilation), and subclinical atherosclerosis at 3 vascular sites (carotid intima-media thickness, coronary artery calcification, and ankle-brachial index). We also evaluated endothelial-related biomarkers previously associated with arsenic. Rice intake was assessed by food frequency questionnaire. Urinary arsenic was measured in 310 participants. A total of 13% of participants consumed ≥1 serving of rice/day. Compared with individuals consuming <1 serving of rice/week, ≥1 serving of rice/day was not associated with subclinical markers after demographic, lifestyle, and CVD risk factor adjustment (eg, geometric mean ratio [95% CI] for hsCRP, 0.98 [0.86-1.11]; aortic distensibility, 0.99 [0.91-1.07]; and carotid intima-media thickness, 0.98 [0.91-1.06]). Associations with urinary arsenic were similar to those for rice intake. Conclusions Rice intake was not associated with subclinical CVD markers in a multiethnic US population. Research using urinary arsenic is needed to assess potential CVD effects of low-level arsenic exposure. Understanding the role of low-level arsenic as it relates to subclinical CVD may contribute to CVD prevention and control.

Age-related declines in α-Klotho drive progenitor cell mitochondrial dysfunction and impaired muscle regeneration

While young muscle is capable of restoring the original architecture of damaged myofibers, aged muscle displays a markedly reduced regeneration. We show that expression of the "anti-aging" protein, α-Klotho, is up-regulated within young injured muscle as a result of transient Klotho promoter demethylation. However, epigenetic control of the Klotho promoter is lost with aging. Genetic inhibition of α-Klotho in vivo disrupted muscle progenitor cell (MPC) lineage progression and impaired myofiber regeneration, revealing a critical role for α-Klotho in the regenerative cascade. Genetic silencing of Klotho in young MPCs drove mitochondrial DNA (mtDNA) damage and decreased cellular bioenergetics. Conversely, supplementation with α-Klotho restored mtDNA integrity and bioenergetics of aged MPCs to youthful levels in vitro and enhanced functional regeneration of aged muscle in vivo in a temporally-dependent manner. These studies identify a role for α-Klotho in the regulation of MPC mitochondrial function and implicate α-Klotho declines as a driver of impaired muscle regeneration with age.

Embryonic-only arsenic exposure alters skeletal muscle satellite cell function in killifish (Fundulus heteroclitus)

Arsenic is a contaminant found worldwide in drinking water and food. Epidemiological studies have correlated arsenic exposure with reduced weight gain and improper muscular development, while in vitro studies show that arsenic exposure impairs myogenic differentiation. The purpose of this study was to use Fundulus heteroclitus or killifish as a model organism to determine if embryonic-only arsenic exposure permanently reduces the number or function of muscle satellite cells. Killifish embryos were exposed to 0, 50, 200, or 800 ppb arsenite (As^III) until hatching, and then juvenile fish were raised in clean water. At 28, 40, and 52 weeks after hatching, skeletal muscle injuries were induced by injecting cardiotoxin into the trunk of the fish just posterior to the dorsal fin. Muscle sections were collected at 0, 3 and 10 days post-injury. Collagen levels were used to assess muscle tissue damage and recovery, while levels of proliferating cell nuclear antigen (PCNA) and myogenin were quantified to compare proliferating cells and newly formed myoblasts. At 28 weeks of age, baseline collagen levels were 105% and 112% greater in 200 and 800 ppb groups, respectively, and at 52 weeks of age, were 58% higher than controls in the 200 ppb fish. After cardiotoxin injury, collagen levels tend to increase to a greater extent and take longer to resolve in the arsenic exposed fish. The number of baseline PCNA(+) cells were 48-216% greater in 800 ppb exposed fish compared to controls, depending on the week examined. However, following cardiotoxin injury, PCNA is reduced at 28 weeks in 200 and 800 ppb fish at day 3 during the recovery period. By 52 weeks, there are significant reductions in PCNA in all exposure groups at day 3 of the recovery period. Based on these results, embryonic arsenic exposure increases baseline collagen levels and PCNA(+) cells in skeletal muscle. However, when these fish are challenged with a muscle injury, the proliferation and differentiation of satellite cells into myogenic precursors is impaired and instead, the fish appear to be favoring a fibrotic resolution to the injury.

Arsenic Induces Members of the mmu-miR-466-669 Cluster Which Reduces NeuroD1 Expression

Chronic arsenic exposure can result in adverse development effects including decreased intellectual function, reduced birth weight, and altered locomotor activity. Previous in vitro studies have shown that arsenic inhibits stem cell differentiation. MicroRNAs (miRNAs) are small noncoding RNAs that regulate multiple cellular processes including embryonic development and cell differentiation. The purpose of this study was to examine whether altered miRNA expression was a mechanism by which arsenic inhibited cellular differentiation. The pluripotent P19 mouse embryonal carcinoma cells were exposed to 0 or 0.5 μM sodium arsenite for 9 days during cell differentiation, and changes in miRNA expression was analyzed using microarrays. We found that the expression of several miRNAs important in cellular differentiation, such as miR-9 and miR-199 were decreased by 1.9- and 1.6-fold, respectively, following arsenic exposure, while miR-92a, miR-291a, and miR-709 were increased by 3-, 3.7-, and 1.6-fold, respectively. The members of the miR-466-669 cluster and its host gene, Scm-like with 4 Mbt domains 2 (Sfmbt2), were significantly induced by arsenic from 1.5- to 4-fold in a time-dependent manner. Multiple miRNA target prediction programs revealed that several neurogenic transcription factors appear to be targets of the cluster. When consensus anti-miRNAs targeting the miR-466-669 cluster were transfected into P19 cells, arsenic-exposed cells were able to more effectively differentiate. The consensus anti-miRNAs appeared to rescue the inhibitory effects of arsenic on cell differentiation due to an increased expression of NeuroD1. Taken together, we conclude that arsenic induces the miR-466-669 cluster, and that this induction acts to inhibit cellular differentiation in part due to a repression of NeuroD1.

Effects of arsenic on adipocyte metabolism: Is arsenic an obesogen?

The environmental obesogen model proposes that in addition to a high-calorie diet and diminished physical activity, other factors such as environmental pollutants and chemicals are involved in the development of obesity. Although arsenic has been recognized as a risk factor for Type 2 Diabetes with a specific mechanism, it is still uncertain whether arsenic is also an obesogen. The impairment of white adipose tissue (WAT) metabolism is crucial in the onset of obesity, and distinct studies have evaluated the effects of arsenic on it, however only in some of them for obesity-related purposes. Thus, the known effects of arsenic on WAT/adipocytes were integrated based on the diverse metabolic and physiological processes that occur in WAT and are altered in obesity, specifically: adipocyte growth, adipokine secretion, lipid metabolism, and glucose metabolism. The currently available information suggests that arsenic can negatively affect WAT metabolism, resulting in arsenic being a potential obesogen.

Tumor-Associated Macrophages Promote Malignant Progression of Breast Phyllodes Tumors by Inducing Myofibroblast Differentiation

Myofibroblast differentiation plays an important role in the malignant progression of phyllodes tumor, a fast-growing neoplasm derived from periductal stromal cells of the breast. Macrophages are frequently found in close proximity with myofibroblasts, but it is uncertain whether they are involved in the myofibroblast differentiation during phyllodes tumor progression. Here we show that increased density of tumor-associated macrophage (TAM) correlates with malignant progression of phyllodes tumor. We found that TAMs stimulated myofibroblast differentiation and promoted the proliferation and invasion of phyllodes tumor cells. Furthermore, we found that levels of the chemokine CCL18 in TAM was an independent prognostic factor of phyllodes tumor. Mechanistic investigations showed that CCL18 promoted expression of α-smooth muscle actin, a hallmark of myofibroblast, along with the proliferation and invasion of phyllodes tumor cells, and that CCL18-driven myofibroblast differentiation was mediated by an NF-κB/miR-21/PTEN/AKT signaling axis. In murine xenograft models of human phyllodes tumor, CCL18 accelerated tumor growth, induced myofibroblast differentiation, and promoted metastasis. Taken together, our findings indicated that TAM drives myofibroblast differentiation and malignant progression of phyllodes tumor through a CCL18-driven signaling cascade amenable to antibody disruption. Cancer Res; 77(13); 3605-18. ©2017 AACR.