Low-dose benzo(a)pyrene and its epoxide metabolite inhibit myogenic differentiation in human skeletal muscle-derived progenitor cells

Exposure to Benzo(a)pyrene promotes proliferation and inhibits differentiation of stromal cells in mice during decidualization

The environmental pollutant Benzo(a)pyrene (BaP) has an adverse effect on the reproductive performance of mammals. We previously showed that BaP treatment during early pregnancy damages endometrial morphology and impairs embryo implantation. Endometrial decidualization at the implantation site (IS) after embryo implantation is crucial for pregnancy maintenance and placental development. The balance between proliferation and differentiation in endometrial stromal cells (ESCs) is a crucial event of decidualization, which is regulated by the cell cycle. Here, we report that abnormal decidualization caused by BaP is associated with cell cycle disturbance of stromal cells. The mice in the treatment group were gavaged with 0.2 mg/kg/day BaP from day 1-8 of pregnancy, while those in control were gavaged with corn oil in parallel. BaP damaged the decidualization of ESCs and reduced the number of polyploid cells. Meanwhile, BaP up-regulated the expression of Ki67 and PCNA, affecting the differentiation of stromal cells. The cell cycle progression analysis during decidualization in vivo and in vitro showed that BaP induced polyploid cells deficiency with enhanced expressions of CyclinA(E)/CDK2, CyclinD/CDK4 and CyclinB/CDK1, which promote the transformation of cells from G₁ to S phase and simultaneously activate the G₂/M phase. The above results indicated that BaP exposure accelerates cell cycle progression, promotes ESC proliferation, inhibits differentiation, and impedes proper decidualization and polyploidy development. Thus, the imbalance of ESC proliferation and differentiation would be an important mechanism for BaP-induced defective decidualization.

Benzo[a]pyrene exposure in muscle triggers sarcopenia through aryl hydrocarbon receptor-mediated reactive oxygen species production

BACKGROUND

Benzo[a]pyrene (BaP), a toxic carcinogen, is associated with various adverse effects but is rarely discussed in muscle-related disorders. This study investigated in vitro and in vivo effects triggered by BaP exposure in muscles and hypothesized that exposure might induce conditions similar to sarcopenia due to the shared mechanism of oxidative stress. In vitro experiments used C2C12 mouse myoblasts to examine effects induced by BaP exposure in control (untreated) and BaP-treated (10 µM/ml) muscle cells. An established TNF-α-treated sarcopenia model was utilized to verify our results. In vivo experiments compared immunohistochemical staining of sarcopenia-related markers in rats exposed to clean air and polluted air.

RESULTS

In C2C12 cells, after 2-72 h of BaP exposure, elevated mRNA and protein expressions were observed in aryl hydrocarbon receptor (AhR) and cytochrome P450 1A1, subsequently in ROS (NOX2 and NOX4) production, inflammatory cytokines (IL-6, TNF-α, and NF-kB), and proteins mediating apoptotic cell death (caspase-3 and PARP). Two myokines also altered mRNA and protein expressions akin to changes in sarcopenia, namely decreased irisin levels and increased myostatin levels. In addition, N-acetylcysteine, a well-known antioxidant, led to decrease in oxidative markers induced by BaP. The validation by TNF-α-treated sarcopenia model revealed comparable biological responses in either TNF-α or BaP treated C2C12 cells. In vivo experiments with rats exposed to air pollution showed increased expression of BaP, AhR, 8-hydroxydeoxyguanosine, and myostatin and decreased irisin expression in immunohistochemical staining.

CONCLUSIONS

Our results suggest that BaP exerts deleterious effects on the muscle, leading to conditions indicative of sarcopenia. Antioxidant supplementation may be a treatment option for BaP-induced sarcopenia, but further validation studies are needed.

Benzo[a]pyrene inhibits myoblast differentiation through downregulating the Hsp70-K2-p38MAPK complex

Cigarette smoking causes skeletal muscle dysfunction and worse prognosis for patients with diverse systemic diseases. Benzo[a]pyrene (BaP), one major constituent that is inhaled during smoking, is particularly known for its ability to impair neurodevelopment, impede reproductivity, or reduce birth weight. Here, we found that BaP exposure led to the inhibition of C2C12 myoblasts differentiation in a dose-dependent manner and reduced the expression of both early and late myogenic differentiation markers. BaP exposure significantly decreased the expression of p38 mitogen-activated protein kinase (p38MAPK), but not AKT, which are both critical during myogenic differentiation. Mechanistically, BaP deregulated the expression levels of MAPK-activated protein kinase 2 (MK2) and heat shock protein 70 (Hsp70), both of which stabilize p38MAPK. Interestingly, treatment of proteasome inhibitor MG132 was able to reverse BaP-induced degradation of Hsp70/ MK2 and p38MAPK in myoblasts, implying BaP-mediated p38MAPK degradation is proteasome-dependent. Overexpression of p38MAPK also rescued the defective differentiation phenotype of C2C12 induced by BaP. Taken together, we suggest that BaP exposure induces MK2/Hsp70/p38MAPK complex degradation in C2C12 myoblasts and impairs myogenic differentiation by proteasomal-dependent mechanisms. As application of the proteasome inhibitor MG132 or overexpression of p38MAPK could reverse impaired differentiation of myoblasts induced by BaP, this may suggest potential related strategies for preventing tobacco-related skeletal muscle diseases or for respiratory rehabilitation.

Benzo[a]pyrene induces fibrotic changes and impairs differentiation in lung stem cells

Human activities have generated air pollution, with extremely small particles (PM 2.5, particulate matter less than 2.5 µm in diameter) and liquid droplets, which become a menace to human health. Among the pollutants, polycyclic aromatic hydrocarbons (PAHs), which enhance the risks of pulmonary dysfunction and cancer development, have been extensively studied. Numerous studies have addressed the effects of PAHs on the respiratory system, whereas the effects on lung stem/progenitor cells remain unknown. Here, we provide evidence that benzo[a]pyrene (BaP), a major toxic PAH, induces fibrotic changes with a loss of α-1,6-fucosylation in CD54⁺CD157⁺CD45^- cells (lung stem cells). In studies with aryl hydrocarbon receptor (AHR) antagonist, we found that these effects by BaP are independent of the canonical AHR pathway. In addition, these BaP-induced fibrotic changes are reduced by TGF-β antagonist, suggesting an alternative pathway of BaP toxicity is different from other PAH/AHR signaling pathways. Finally, it was observed that BaP impairs the spheroid formation and the podoplanin expression of CD54⁺CD157⁺CD45^- cells, indicating that BaP suppresses the differentiation of lung stem cells. Taken together, our findings reveal specific BaP-induced injuries in CD54⁺CD157⁺CD45^- cells.

Effects of environmental stressors on stem cells

Environmental toxicants are ubiquitous, and many are known to cause harmful health effects. However, much of what we know or think we know concerning the targets and long-term effects of exposure to environmental stressors is sadly lacking. Toxicant exposure may have health effects that are currently mischaracterized or at least mechanistically incompletely understood. While much of the recent excitement about stem cells (SCs) focuses on their potential as therapeutic agents, they also offer a valuable resource to give us insight into the mechanisms and risks of toxicant effects. Not only as a response to the increasing ethical pressure to reduce animal testing, SC studies allow us valuable insight into the true effects of human exposure to environmental stressors under controlled conditions. We present a review of the history of publications on the effects of environmental stressors on SCs, followed by a consolidation of the literature over the past five years on a subset of key environmental stressors of importance to human health and their effects on both embryonic and tissue SCs. The review will make constructive suggestions as to areas of toxicant research where further studies are needed, as well as making indications of the potential utility for advancing knowledge and directing research on environmental toxicology.

Adverse effects of acrolein, a ubiquitous environmental toxicant, on muscle regeneration and mass

BACKGROUND

Acrolein is an extremely electrophilic aldehyde. Increased urinary acrolein adducts have been found in type 2 diabetic patients and people with a smoking habit. The increased blood acrolein was shown in patients who received the cancer drug cyclophosphamide. Both diabetes and smoking are risk factors for skeletal muscle wasting or atrophy. Acrolein has been found to induce myotube atrophy in vitro. The in vitro and in vivo effects and mechanisms of acrolein on myogenesis and the in vivo effect of acrolein on muscle wasting still remain unclear.

METHODS

C2C12 myoblasts were used to assess the effects of low-dose acrolein (0.125-1 μM) on myogenesis in vitro. Mice were exposed daily to acrolein in distilled water by oral administration (2.5 and 5 mg/kg) for 4 weeks with or without glycerol-induced muscle injury to investigate the effects of acrolein on muscle wasting and regeneration.

RESULTS

Non-cytotoxic-concentration acrolein dose dependently inhibited myogenic differentiation in myoblasts (myotube formation inhibition: 0.5 and 1 μM, 66.25% and 46.25% control, respectively, n = 4, P < 0.05). The protein expression for myogenesis-related signalling molecules (myogenin and phosphorylated Akt: 0.5 and 1 μM, 85.15% and 51.52% control and 62.63% and 56.57% control, respectively, n = 4, P < 0.05) and myosin heavy chain (MHC: 0.5 and 1 μM, 63.64% and 52.53% control, n = 4, P < 0.05) were decreased in acrolein-treated myoblasts. Over-expression of the constitutively active form of Akt in myoblasts during differentiation prevented the inhibitory effects of acrolein (1 μM) on myogenesis (MHC and myogenin protein expression: acrolein with or without constitutively active Akt, 64.65% and 105.21% control and 69.14% and 102.02% control, respectively, n = 5, P < 0.05). Oral administration of acrolein for 4 weeks reduced muscle weights (5 mg/kg/day: 65.52% control, n = 6, P < 0.05) and cross-sectional area of myofibers in soleus muscles (5 mg/kg/day: 79.92% control, n = 6, P < 0.05) with an up-regulation of atrogin-1 and a down-regulation of phosphorylated Akt protein expressions. Acrolein retarded soleus muscle regeneration in a glycerol-induced muscle regeneration mouse model (5 mg/kg/day: 49.29% control, n = 4, P < 0.05). Acrolein exposure reduced muscle endurance during rotarod fatigue performance in mice with or without glycerol-induced muscle injury (5 mg/kg/day without glycerol: 30.43% control, n = 4, P < 0.05). Accumulation of acrolein protein adducts could be detected in the soleus muscles of acrolein-treated mice.

CONCLUSIONS

Low-dose acrolein significantly inhibited myogenic differentiation in vitro, which might be through inhibition of Akt signalling. Acrolein induced muscle wasting and retarded muscle regeneration in mice. These results suggest that acrolein may be a risk factor for myogenesis and disease-related myopathy.

Effect of Benzo[a]pyrene-DNA Adduct in Cord Blood on the Neurodevelopment of 12-Month-Old Infants in Qingdao City

INTRODUCTION

The study was designed to explore the possible adverse effects of prenatal polycyclic aromatic hydrocarbons (PAHs) on the neurodevelopment of the infants at the age of 12 months in a birth cohort in Qingdao of China. Benzo[a]pyrene (BaP)-DNA adduct level in umbilical cord blood was measured by enzyme immunoassay.

METHODS

Child neurodevelopment was assessed at both 6 months and 12 months of age using the Gesell Development Inventory (GDI).

RESULTS

This study results reveal that multivariate linear analysis, cord BaP-DNA adduct level was inversely associated with developmental quotient score in the adaptive domain [β = -0.08; 95% CI: (-0.16, -0.003); p = 0.04], gross motor domain [β = -0.10; 95% CI: (-0.20, -0.01); p = 0.02], fine motor domain [β = -0.15; 95% CI: (-0.25, -0.05); p = 0.01], language domain [β = -0.12; 95% CI: (-0.21, -0.03); p = 0.02], and personal-social domain [β = -0.13; 95% CI: (-0.22, -0.04); p<0.01]. Further, multivariate logistic regression analysis showed increased cord BaP-DNA adduct levels associated with increased odds of delayed in language domain.

CONCLUSION

In conclusion, the study suggested that prenatal PAH exposure monitored by umbilical cord blood BaP-DNA adducts may adversely affect the neurodevelopment of the infants at 12 months of age.

Preventing muscle wasting by osteoporosis drug alendronate in vitro and in myopathy models via sirtuin-3 down-regulation

BACKGROUND

A global consensus on the loss of skeletal muscle mass and function in humans refers as sarcopenia and cachexia including diabetes, obesity, renal failure, and osteoporosis. Despite a current improvement of sarcopenia or cachexia with exercise training and supportive therapies, alternative and specific managements are needed to discover for whom are unable or unwilling to embark on these treatments. Alendronate is a widely used drug for osteoporosis in the elderly and postmenopausal women. Osteopenic menopausal women with 6 months of alendronate therapy have been observed to improve not only lumbar bone mineral density but also handgrip strength. However, the effect and mechanism of alendronate on muscle strength still remain unclear. Here, we investigated the therapeutic potential and the molecular mechanism of alendronate on the loss of muscle mass and strength in vitro and in vivo.

METHODS

Mouse myoblasts and primary human skeletal muscle-derived progenitor cells were used to assess the effects of low-dose alendronate (0.1-1 μM) combined with or without dexamethasone on myotube hypertrophy and myogenic differentiation. Moreover, we also evaluated the effects of low-dose alendronate (0.5 and 1 mg/kg) by oral administration on the limb muscle function and morphology of mice with denervation-induced muscle atrophy and glycerol-induced muscle injury.

RESULTS

Alendronate inhibited dexamethasone-induced myotube atrophy and myogenic differentiation inhibition in mouse myoblasts and primary human skeletal muscle-derived progenitor cells. Alendronate significantly abrogated dexamethasone-up-regulated sirtuin-3 (SIRT3), but not SIRT1, protein expression in myotubes. Both SIRT3 inhibitor AKG7 and SIRT3-siRNA transfection could also reverse dexamethasone-up-regulated atrogin-1 and SIRT3 protein expressions. Animal studies showed that low-dose alendronate by oral administration ameliorated the muscular malfunction in mouse models of denervation-induced muscle atrophy and glycerol-induced muscle injury with a negative regulation of SIRT3 expression.

CONCLUSIONS

The putative mechanism by which muscle atrophy was improved with alendronate might be through the SIRT3 down-regulation. These findings suggest that alendronate can be a promising therapeutic strategy for management of muscle wasting-related diseases and sarcopenia.

2,3,7,8-Tetrachlorodibenzo-p-dioxin induces alterations in myogenic differentiation of C2C12 cells

Dioxin-induced toxicities that affect the development of the motor system have been proposed since many years. However, cellular evidence and the molecular basis for the effects are limited. In this study, a cultured mouse myoblast cell line, C2C12, was utilized to examine the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on myogenic differentiation and expression of acetylcholinesterase (AChE), a neuromuscular transmission-related gene. The results showed that TCDD exposure at 10^-10 M repressed the myotube formation of C2C12 cells by disturbing the fusion process and suppressing the expression of myosin heavy chain, a myobute structural protein, and not by induction of cytotoxicity. Furthermore, TCDD dose dependently suppressed the transcriptional expression and enzymatic activity of AChE during the myogenic differentiation, particularly in the middle stage. However, the administration of aryl hydrocarbon receptor antagonists, CH223191 and alpha-naphthoflavone, did not completely reverse the TCDD-induced downregulation of muscular AChE during myogenic differentiation. These findings suggest that low dose exposure to dioxin may result in disturbances of muscle differentiation and neuromuscular transmission.

Effect of enrofloxacin on the proteome of earthworms

The environmental and human health risks of veterinary drugs are becoming public health issues. Enrofloxacin (EF) is an extensively used animal-specific antibacterial agent that leaves drug residues in the environment. This study investigated the proteomic response of the earthworm Eisenia fetida to EF exposure. Earthworms were exposed to EF in soil at 1-500mg·kg^-1, and samples were collected at intervals during a 28 day period. The extracted proteins were separated by two dimensional electrophoresis to detect differentially expressed proteins (DEPs) in EF-exposed earthworms. In total, 35 unique DEPs were found. These proteins were subjected to MALDI-TOF/TOF-MS analysis and identified through comparison of their mass spectra with those in protein databases. The DEPs were grouped on the basis of their function, into metabolism, stress-related, transport, transcription, and predicted/hypothetical protein categories. Knowledge of proteins that are induced or repressed by EF in earthworms could provide insight into mechanisms of sub-clinical physiological effects of xenobiotic residues in the environment, and may also help understand synergy between pollutants. As several DEPs in E. fetida showed similarity to human protein sequences, E. fetida has potential as an indicator species to assess the environmental and biological risks of drug residues.

Transplantation of human skeletal muscle-derived progenitor cells ameliorates knee osteoarthritis in streptozotocin-induced diabetic mice

The epidemiological and experimental evidence suggests that diabetes can be an independent risk factor for osteoarthritis. The osteoarthritis-like cartilage damage has been shown in streptozotocin-induced diabetic mice. The therapeutic effects of human skeletal muscle-derived progenitor cells (HSMPCs) on diabetic osteoarthritis still remain unclear. Here, we investigated the therapeutic potential of HSMPCs on diabetic knee osteoarthritis. The in vitro chondrogenic ability of HSMPCs was determined by pellet culture assay. Male mice were used to develop the model of streptozotocin-induced type 1 diabetes and its related osteoarthritis. HSMPCs were injected intra-articularly to rescue osteoarthritis. Protein expressions of advanced glycation end-products, cyclooxygenase-2, and type-2 collagen in tissues were determined by immunohistochemistry. The pellet culture assay showed that HSMPCs cultured in differentiation medium for chondrogenesis significantly produced larger pellets with an overproduction of extracellular matrix than in growth medium. In in vivo experiments, intra-articular injection of HSMPCs for 4 weeks significantly prevented the progression of degenerative changes in the cartilage of streptozotocin-induced diabetic mice, including an obvious increase of total articular cartilage thickness and a decrease of fibrous cartilage thickness. HSMPCs transplantation also exerted the decline in advanced glycation end-products and cyclooxygenase-2 protein expression, but increased the type-2 collagen protein expression in streptozotocin-induced osteoarthritic cartilages. Moreover, HSMPCs transplantation also inhibited the increased serum interleukin-6 and matrix metalloproteinase-3 levels in diabetic mice. These results demonstrated for the first time that HSMPCs transplantation ameliorates cartilage degeneration in diabetes-related osteoarthritis mice. These findings suggest that HSMPCs transplantation may apply as a potential therapeutic use of diabetes-related osteoarthritis. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1886-1893, 2017.

Development and validation of a HPLC method for the determination of benzo(a)pyrene in human breast milk

A simple analytical procedure was developed for the quantitation of benzo(a)pyrene in human breast milk using solid phase extraction (SPE) combined with high performance liquid chromatography. Before the chromatographic process, SPE, including C18 functional groups in silicagel cartridges, was conducted for sample preparation. A C18 column (100×4.6 mm id, 3 μm particle size) was used with acetonitrile:water (80:20) as the mobile phase at a flow rate 1mL/min at 30°C. Fluorimetric detection was performed for excitation and emission at 290 and 406 nm, respectively. It was observed that the calibration curve was linear over the range of 0.5-80 ng/mL. The limit of detection and limit of quantitation were found to be 0.5 and 1.07 ng/mL, respectively. Intraday and interday relative standard deviation values were less than 5.15%. Moreover, the newly developed method provides a fast, simple, cost effective, and sensitive assay to detect an important carcinogen substance, benzo(a)pyrene, in human breast milk.

Advanced glycation end-products induce skeletal muscle atrophy and dysfunction in diabetic mice via a RAGE-mediated, AMPK-down-regulated, Akt pathway

Diabetic myopathy, a less studied complication of diabetes, exhibits the clinical observations characterized by a less muscle mass, muscle weakness and a reduced physical functional capacity. Accumulation of advanced glycation end-products (AGEs), known to play a role in diabetic complications, has been identified in ageing human skeletal muscles. However, the role of AGEs in diabetic myopathy remains unclear. Here, we investigated the effects of AGEs on myogenic differentiation and muscle atrophy in vivo and in vitro. We also evaluated the therapeutic potential of alagebrium chloride (Ala-Cl), an inhibitor of AGEs. Muscle fibre atrophy and immunoreactivity for AGEs, Atrogin-1 (a muscle atrophy marker) and phosphorylated AMP-activated protein kinase (AMPK) expressions were markedly increased in human skeletal muscles from patients with diabetes as compared with control subjects. Moreover, in diabetic mice we found increased blood AGEs, less muscle mass, lower muscular endurance, atrophic muscle size and poor regenerative capacity, and increased levels of muscle AGE and receptor for AGE (RAGE), Atrogin-1 and phosphorylated AMPK, which could be significantly ameliorated by Ala-Cl. Furthermore, in vitro, AGEs (in a dose-dependent manner) reduced myotube diameters (myotube atrophy) and induced Atrogin-1 protein expression in myotubes differentiated from both mouse myoblasts and primary human skeletal muscle-derived progenitor cells. AGEs exerted a negative regulation of myogenesis of mouse and human myoblasts. Ala-Cl significantly inhibited the effects of AGEs on myotube atrophy and myogenesis. We further demonstrated that AGEs induced muscle atrophy/myogenesis impairment via a RAGE-mediated AMPK-down-regulation of the Akt signalling pathway. Our findings support that AGEs play an important role in diabetic myopathy, and that an inhibitor of AGEs may offer a therapeutic strategy for managing the dysfunction of muscle due to diabetes or ageing.