Myostatin induces DNA damage in skeletal muscle of streptozotocin-induced type 1 diabetic mice.

One of the features of uncontrolled type 1 diabetes is oxidative stress that induces DNA damage and cell death. Skeletal muscle atrophy is also considerable in type 1 diabetes, however, the signaling mechanisms that induce oxidative stress culminating in muscle atrophy are not fully known. Here, we show that in Streptozotocin-induced diabetic wild type mice, hypo-phosphorylation of Akt, resulted in activation of Foxa2 transcription factor in the muscle. Foxa2 transcriptionally up-regulated Myostatin, contributing to exaggerated oxidative stress leading to DNA damage via p63/REDD1 pathway in skeletal muscle of Streptozotocin-treated wild type mice. In Myostatin(-/-) mice however, Streptozotocin treatment did not reduce Akt phosphorylation despite reduced IRS-1 signaling. Moreover, Foxa2 levels remained unaltered in Myostatin(-/-) mice, while levels of p63/REDD1 were higher compared with wild type mice. Consistent with these results, relatively less DNA damage and muscle atrophy was observed in Myostatin(-/-) muscle in response to Streptozotocin treatment. Taken together, our results for the first time show the role of Foxa2 in Myostatin regulation in skeletal muscle in diabetic mice. Altogether, these results demonstrate the mechanism by which Myostatin contributes to DNA damage in skeletal muscle of the diabetic mice that would lead to myofiber degeneration.

Muscle-specific microRNA1 (miR1) targets heat shock protein 70 (HSP70) during dexamethasone-mediated atrophy.

High doses of dexamethasone (Dex) or myostatin (Mstn) induce severe atrophy of skeletal muscle. Here we show a novel microRNA1 (miR1)-mediated mechanism through which Dex promotes skeletal muscle atrophy. Using both C2C12 myotubes and mouse models of Dex-induced atrophy we show that Dex induces miR1 expression through glucocorticoid receptor (GR). We further show that Mstn treatment facilitates GR nuclear translocation and thereby induces miR1 expression. Inhibition of miR1 in C2C12 myotubes attenuated the Dex-induced increase in atrophy-related proteins confirming a role for miR1 in atrophy. Analysis of miR1 targets revealed that HSP70 is regulated by miR1 during atrophy. Our results demonstrate that increased miR1 during atrophy reduced HSP70 levels, which resulted in decreased phosphorylation of AKT, as HSP70 binds to and protects phosphorylation of AKT. We further show that loss of pAKT leads to decreased phosphorylation, and thus, enhanced activation of FOXO3, up-regulation of MuRF1 and Atrogin-1, and progression of skeletal muscle atrophy. Based on these results, we propose a model whereby Dex- and Mstn-mediated atrophic signals are integrated through miR1, which then either directly or indirectly, inhibits the proteins involved in providing protection against atrophy.

Contributions of Astrocyte and Neuronal Volume to CA1 Neuron Excitability Changes in Elevated Extracellular Potassium.

Rapid increases in cell volume reduce the size of the extracellular space (ECS) and are associated with elevated brain tissue excitability. We recently demonstrated that astrocytes, but not neurons, rapidly swell in elevated extracellular potassium (∧[K+] o ) up to 26 mM. However, effects of acute astrocyte volume fluctuations on neuronal excitability in ∧[K+] o have been difficult to evaluate due to direct effects on neuronal membrane potential and generation of action potentials. Here we set out to isolate volume-specific effects occurring in ∧[K+] o on CA1 pyramidal neurons in acute hippocampal slices by manipulating cell volume while recording neuronal glutamate currents in 10.5 mM [K+] o + tetrodotoxin (TTX) to prevent neuronal firing. Elevating [K+] o to 10.5 mM induced astrocyte swelling and produced significant increases in neuronal excitability in the form of mixed α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/N-methyl-D-aspartate (NMDA) receptor mEPSCs and NMDA receptor-dependent slow inward currents (SICs). Application of hyperosmolar artificial cerebrospinal fluid (ACSF) by addition of mannitol in the continued presence of 10.5 mM K+ forced shrinking of astrocytes and to a lesser extent neurons, which resisted swelling in ∧[K+] o . Cell shrinking and dilation of the ECS significantly dampened neuronal excitability in 10.5 mM K+. Subsequent removal of mannitol amplified effects on neuronal excitability and nearly doubled the volume increase in astrocytes, presumably due to continued glial uptake of K+ while mannitol was present. Slower, larger amplitude events mainly driven by NMDA receptors were abolished by mannitol-induced expansion of the ECS. Collectively, our findings suggest that cell volume regulation of the ECS in elevated [K+] o is driven predominantly by astrocytes, and that cell volume effects on neuronal excitability can be effectively isolated in elevated [K+] o conditions.

Novel live cell fluorescent probe for human-induced pluripotent stem cells highlights early reprogramming population.

BACKGROUND: Despite recent rapid progress in method development and biological understanding of induced pluripotent stem (iPS) cells, there has been a relative shortage of tools that monitor the early reprogramming process into human iPS cells. METHODS: We screened the in-house built fluorescent library compounds that specifically bind human iPS cells. After tertiary screening, the selected probe was analyzed for its ability to detect reprogramming cells in the time-dependent manner using high-content imaging analysis. The probe was compared with conventional dyes in different reprogramming methods, cell types, and cell culture conditions. Cell sorting was performed with the fluorescent probe to analyze the early reprogramming cells for their pluripotent characteristics and genome-wide gene expression signatures by RNA-seq. Finally, the candidate reprogramming factor identified was investigated for its ability to modulate reprogramming efficiency. RESULTS: We identified a novel BODIPY-derived fluorescent probe, BDL-E5, which detects live human iPS cells at the early reprogramming stage. BDL-E5 can recognize authentic reprogramming cells around 7 days before iPS colonies are formed and stained positive with conventional pluripotent markers. Cell sorting of reprogrammed cells with BDL-E5 allowed generation of an increased number and higher quality of iPS cells. RNA sequencing analysis of BDL-E5-positive versus negative cells revealed early reprogramming patterns of gene expression, which notably included CREB1. Reprogramming efficiency was significantly increased by overexpression of CREB1 and decreased by knockdown of CREB1. CONCLUSION: Collectively, BDL-E5 offers a valuable tool for delineating the early reprogramming pathway and clinically applicable commercial production of human iPS cells.

Oxidative stress mediates depot-specific functional differences of human adipose-derived stem cells.

BACKGROUND: Visceral (VS) fat depot is known to have defective adipogenic functions compared to subcutaneous (SC) fat, but its mechanism of origin is unclear. OBJECTIVE: We tested our hypothesis that the degree of oxidative stress in adipose-derived stem cells (ASCs) from these depots may account for this difference. METHODS: ASCs were isolated from VS (omental region) and SC (abdominal region) fat depots of human subjects undergoing bariatric surgery. ASCs from VS and SC fat were investigated for their cellular characteristics in reactive oxygen species (ROS), metabolism, gene expression, proliferation, senescence, migration, and adipocyte differentiation. ASCs were also treated with antioxidant ascorbic acid (vitamin C). RESULTS: We found that human VS-derived ASCs exhibit excessive oxidative stress characterized by high reactive oxygen species (ROS), compared to SC-derived ASCs. Gene expression analyses indicate that the VS-ASCs exhibit higher levels of genes involved in pro-oxidant and pro-inflammatory pathways and lower levels of genes in antioxidant and anti-inflammatory pathways. VS-ASCs have impaired cellular functions compared to SC-ASCs, such as slower proliferation, early senescence, less migratory activity, and poor adipogenic capability in vitro. Treatment with ascorbic acid decreased ROS levels drastically in VS-ASCs. Ascorbic acid treatment substantially improved proliferation, senescence, migration, and adipogenic capacities of compromised ASCs caused by high ROS. CONCLUSIONS: This finding suggests the fat depot-specific differences of cellular defects originating from stem cell population. Considering clinical potentials of human ASCs for cell therapies, this also offers a possible strategy for improving their therapeutic qualities through antioxidants.

Amenable epigenetic traits of dental pulp stem cells underlie high capability of xeno-free episomal reprogramming.

BACKGROUND: While a shift towards non-viral and animal component-free methods of generating induced pluripotent stem (iPS) cells is preferred for safer clinical applications, there is still a shortage of reliable cell sources and protocols for efficient reprogramming. METHODS: Here, we show a robust episomal and xeno-free reprogramming strategy for human iPS generation from dental pulp stem cells (DPSCs) which renders good efficiency (0.19%) over a short time frame (13-18 days). RESULTS: The robustness of DPSCs as starting cells for iPS induction is found due to their exceptional inherent stemness properties, developmental origin from neural crest cells, specification for tissue commitment, and differentiation capability. To investigate the epigenetic basis for the high reprogramming efficiency of DPSCs, we performed genome-wide DNA methylation analysis and found that the epigenetic signature of DPSCs associated with pluripotent, developmental, and ecto-mesenchymal genes is relatively close to that of iPS and embryonic stem (ES) cells. Among these genes, it is found that overexpression of PAX9 and knockdown of HERV-FRD improved the efficiencies of iPS generation. CONCLUSION: In conclusion, our study provides underlying epigenetic mechanisms that establish a robust platform for efficient generation of iPS cells from DPSCs, facilitating industrial and clinical use of iPS technology for therapeutic needs.

Diffuse Optical Spectroscopy and Imaging to Detect and Quantify Adipose Tissue Browning.

Adipose (fat) tissue is a complex metabolic organ that is highly active and essential. In contrast to white adipose tissue (WAT), brown adipose tissue (BAT) is deemed metabolically beneficial because of its ability to burn calories through heat production. The conversion of WAT-resident adipocytes to "beige" or "brown-like" adipocytes has recently attracted attention. However, it typically takes a few days to analyze and confirm this browning of WAT through conventional molecular, biochemical, or histological methods. Moreover, accurate quantification of the overall browning process is not possible by any of these methods. In this context, we report the novel application of diffuse reflectance spectroscopy (DRS) and multispectral imaging (MSI) to detect and quantify the browning process in mice. We successfully demonstrated the time-dependent increase in browning of WAT, following its induction through ß-adrenergic agonist injections. The results from these optical techniques were confirmed with those of standard molecular and biochemical assays, which measure gene and protein expression levels of UCP1 and PGC-1α, as well as with histological examinations. We envision that the reported optical methods can be developed into a fast, real time, cost effective and easy to implement imaging approach for quantification of the browning process in adipose tissue.

Retinoic acid is abundantly detected in different depots of adipose tissue by SERS.

Retinoic acid (RA) is essential for early developmental processes and stem cell differentiation, but less is known about its contributions to adult tissues and stem cells including adipose tissue. We previously demonstrated that many genes involved in RA synthesis and downstream pathway are differentially expressed in adipose-derived stem cells (ASCs) from visceral fat compared to those from subcutaneous fat, leading to changes in their early adipogenic functions. In order to study potential contributions of RA in adipose tissue, we measured tissue RA levels using a technique based on surface-enhanced Raman spectroscopy (SERS). The data indicate heretofore underappreciated abundance of endogenous RA in mouse adipose tissue compared to other tissues and dynamic changes of RA concentrations after high fat diet feeding. Our results lay the foundation for further investigation on the functional role of RA in adipose tissue development and metabolism.

Retinoic Acid Mediates Visceral-Specific Adipogenic Defects of Human Adipose-Derived Stem Cells.

Increased visceral fat, rather than subcutaneous fat, during the onset of obesity is associated with a higher risk of developing metabolic diseases. The inherent adipogenic properties of human adipose-derived stem cells (ASCs) from visceral depots are compromised compared with those of ASCs from subcutaneous depots, but little is known about the underlying mechanisms. Using ontological analysis of global gene expression studies, we demonstrate that many genes involved in retinoic acid (RA) synthesis or regulated by RA are differentially expressed in human tissues and ASCs from subcutaneous and visceral fat. The endogenous level of RA is higher in visceral ASCs; this is associated with upregulation of the RA synthesis gene through the visceral-specific developmental factor WT1. Excessive RA-mediated activity impedes the adipogenic capability of ASCs at early but not late stages of adipogenesis, which can be reversed by antagonism of RA receptors or knockdown of WT1. Our results reveal the developmental origin of adipocytic properties and the pathophysiological contributions of visceral fat depots.

Adipocyte Ceramides Regulate Subcutaneous Adipose Browning, Inflammation, and Metabolism.

Adipocytes package incoming fatty acids into triglycerides and other glycerolipids, with only a fraction spilling into a parallel biosynthetic pathway that produces sphingolipids. Herein, we demonstrate that subcutaneous adipose tissue of type 2 diabetics contains considerably more sphingolipids than non-diabetic, BMI-matched counterparts. Whole-body and adipose tissue-specific inhibition/deletion of serine palmitoyltransferase (Sptlc), the first enzyme in the sphingolipid biosynthesis cascade, in mice markedly altered adipose morphology and metabolism, particularly in subcutaneous adipose tissue. The reduction in adipose sphingolipids increased brown and beige/brite adipocyte numbers, mitochondrial activity, and insulin sensitivity. The manipulation also increased numbers of anti-inflammatory M2 macrophages in the adipose bed and induced secretion of insulin-sensitizing adipokines. By comparison, deletion of serine palmitoyltransferase from macrophages had no discernible effects on metabolic homeostasis or adipose function. These data indicate that newly synthesized adipocyte sphingolipids are nutrient signals that drive changes in the adipose phenotype to influence whole-body energy expenditure and nutrient metabolism.

Myostatin augments muscle-specific ring finger protein-1 expression through an NF-kB independent mechanism in SMAD3 null muscle.

Smad (Sma and Mad-related protein) 2/3 are downstream signaling molecules for TGF-ß and myostatin (Mstn). Recently, Mstn was shown to induce reactive oxygen species (ROS) in skeletal muscle via canonical Smad3, nuclear factor-κB, and TNF-α pathway. However, mice lacking Smad3 display skeletal muscle atrophy due to increased Mstn levels. Hence, our aims were first to investigate whether Mstn induced muscle atrophy in Smad3(-/-) mice by increasing ROS and second to delineate Smad3-independent signaling mechanism for Mstn-induced ROS. Herein we show that Smad3(-/-) mice have increased ROS levels in skeletal muscle, and inactivation of Mstn in these mice partially ablates the oxidative stress. Furthermore, ROS induction by Mstn in Smad3(-/-) muscle was not via nuclear factor-κB (p65) signaling but due to activated p38, ERK MAPK signaling and enhanced IL-6 levels. Consequently, TNF-α, nicotinamide adenine dinucleotide phosphate oxidase, and xanthine oxidase levels were up-regulated, which led to an increase in ROS production in Smad3(-/-) skeletal muscle. The exaggerated ROS in the Smad3(-/-) muscle potentiated binding of C/EBP homology protein transcription factor to MuRF1 promoter, resulting in enhanced MuRF1 levels leading to muscle atrophy.

Modulation of reactive oxygen species in skeletal muscle by myostatin is mediated through NF-κB.

Abnormal levels of reactive oxygen species (ROS) and inflammatory cytokines have been observed in the skeletal muscle during muscle wasting including sarcopenia. However, the mechanisms that signal ROS production and prolonged maintenance of ROS levels during muscle wasting are not fully understood. Here, we show that myostatin (Mstn) is a pro-oxidant and signals the generation of ROS in muscle cells. Myostatin, a transforming growth factor-ß (TGF-ß) family member, has been shown to play an important role in skeletal muscle wasting by increasing protein degradation. Our results here show that Mstn induces oxidative stress by producing ROS in skeletal muscle cells through tumor necrosis factor-α (TNF-α) signaling via NF-κB and NADPH oxidase. Aged Mstn null (Mstn(-/-) ) muscles, which display reduced sarcopenia, also show an increased basal antioxidant enzyme (AOE) levels and lower NF-κB levels indicating efficient scavenging of excess ROS. Additionally, our results indicate that both TNF-α and hydrogen peroxide (H(2) O(2) ) are potent inducers of Mstn and require NF-κB signaling for Mstn induction. These results demonstrate that Mstn and TNF-α are components of a feed forward loop in which Mstn triggers the generation of second messenger ROS, mediated by TNF-α and NADPH oxidase, and the elevated TNF-α in turn stimulates Mstn expression. Higher levels of Mstn in turn induce muscle wasting by activating proteasomal-mediated catabolism of intracellular proteins. Thus, we propose that inhibition of ROS induced by Mstn could lead to reduced muscle wasting during sarcopenia.