Extraocular muscle stem cells exhibit distinct cellular properties associated with non-muscle molecular signatures

Skeletal muscle stem cells (MuSCs) are recognised as functionally heterogeneous. Cranial MuSCs are reported to have greater proliferative and regenerative capacity when compared with those in the limb. A comprehensive understanding of the mechanisms underlying this functional heterogeneity is lacking. Here, we have used clonal analysis, live imaging and single cell transcriptomic analysis to identify crucial features that distinguish extraocular muscle (EOM) from limb muscle stem cell populations. A MyogeninntdTom reporter showed that the increased proliferation capacity of EOM MuSCs correlates with deferred differentiation and lower expression of the myogenic commitment gene Myod. Unexpectedly, EOM MuSCs activated in vitro expressed a large array of extracellular matrix components typical of mesenchymal non-muscle cells. Computational analysis underscored a distinct co-regulatory module, which is absent in limb MuSCs, as driver of these features. The EOM transcription factor network, with Foxc1 as key player, appears to be hardwired to EOM identity as it persists during growth, disease and in vitro after several passages. Our findings shed light on how high-performing MuSCs regulate myogenic commitment by remodelling their local environment and adopting properties not generally associated with myogenic cells.

SIRT6 pharmacological inhibition delays skin cancer progression in the squamous cell carcinoma

Sirtuin 6 (SIRT6) has a critical role in cutaneous Squamous Cell Carcinoma (cSCC): SIRT6 silencing in skin SCC cells has pro-differentiating effects and SIRT6 deletion abrogated DMBA-TPA-induced skin tumorigenesis in mice. On the other hand, SIRT6 acts as tumor suppressor in SCC by enhancing glycolysis in tumor propagating cells. Herein, pharmacological modulation of SIRT6 deacetylase activity was investigated in cSCC, with S6 (inhibitor) or MDL-800 (activator). In cSCC cells, S6 recreated the pro-differentiating effects of SIRT6 silencing, as the levels of Keratin 1, Keratin 10 and Loricrin were upregulated compared to controls. Next, the effects of SIRT6 pharmacological modulation were evaluated in a DMBA-TPA-induced skin cancer mouse model. Mice treated with the inhibitor S6 in a preventive approach, i.e. at the beginning of the promotion stage, presented reduced number and size of papillomas, compared to the controls. The epidermal hyperproliferation marker Keratin 6 and the cSCC marker Keratin 8 were less abundant when SIRT6 was inhibited. In S6-treated lesions, the Epithelial-Mesenchymal Transition (EMT) markers Zeb1 and Vimentin were less expressed compared to untreated lesions. In a therapeutic approach, i.e. treatment starting after papilloma appearance, the S6 group presented reduced papillomas (number and size), whereas MDL-800-treated mice displayed an opposite trend. In S6-treated lesions, Keratin 6 and Keratin 8 were less expressed, EMT was less advanced, with a higher E-cadherin/Vimentin ratio, indicating a delayed carcinogenesis when SIRT6 was inhibited. Our results confirm that SIRT6 plays a role in skin carcinogenesis and suggest SIRT6 pharmacological inhibition as a promising strategy in cSCC.

Thyroid Hormone Regulates the Lipid Content of Muscle Fibers, Thus Affecting Physical Exercise Performance

Skeletal muscle (SkM) lipid composition plays an essential role in physiological muscle maintenance and exercise performance. Thyroid hormones (THs) regulate muscle formation and fuel energy utilization by modulating carbohydrates and lipid and protein metabolism. The best-known effects of THs in SkM include the promotion of mitochondrial biogenesis, the fiber-type switch from oxidative to glycolytic fibers, and enhanced angiogenesis. To assess the role of THs on the lipidic composition of SkM fibers, we performed lipidomic analyses of SkM cells and tissues, glucose tolerance experiments, and exercise performance tests. Our data demonstrated that TH treatment induces remodeling of the lipid profile and changes the proportion of fatty acids in SkM. In brief, THs significantly reduced the ratio of stearic/oleic acid in the muscle similar to what is induced by physical activity. The increased proportion of unsaturated fatty acids was linked to an improvement in insulin sensitivity and endurance exercise. These findings point to THs as critical endocrine factors affecting exercise performance and indicate that homeostatic maintenance of TH signals, by improving cell permeability and receptor stability at the cell membrane, is crucial for muscle physiology.

Loss of p53 activates thyroid hormone via type 2 deiodinase and enhances DNA damage

The Thyroid Hormone (TH) activating enzyme, type 2 Deiodinase (D2), is functionally required to elevate the TH concentration during cancer progression to advanced stages. However, the mechanisms regulating D2 expression in cancer still remain poorly understood. Here, we show that the cell stress sensor and tumor suppressor p53 silences D2 expression, thereby lowering the intracellular THs availability. Conversely, even partial loss of p53 elevates D2/TH resulting in stimulation and increased fitness of tumor cells by boosting a significant transcriptional program leading to modulation of genes involved in DNA damage and repair and redox signaling. In vivo genetic deletion of D2 significantly reduces cancer progression and suggests that targeting THs may represent a general tool reducing invasiveness in p53-mutated neoplasms.

Cardiovascular and Neuronal Consequences of Thyroid Hormones Alterations in the Ischemic Stroke

Ischemic stroke is one of the leading global causes of neurological morbidity and decease. Its etiology depends on multiple events such as cardiac embolism, brain capillaries occlusion and atherosclerosis, which ultimately culminate in blood flow interruption, incurring hypoxia and nutrient deprivation. Thyroid hormones (THs) are pleiotropic modulators of several metabolic pathways, and critically influence different aspects of tissues development. The brain is a key TH target tissue and both hypo- and hyperthyroidism, during embryonic and adult life, are associated with deranged neuronal formation and cognitive functions. Accordingly, increasing pieces of evidence are drawing attention on the consistent relationship between the THs status and the acute cerebral and cardiac diseases. However, the concrete contribution of THs systemic or local alteration to the pathology outcome still needs to be fully addressed. In this review, we aim to summarize the multiple influences that THs exert on the brain and heart patho-physiology, to deepen the reasons for the harmful effects of hypo- and hyperthyroidism on these organs and to provide insights on the intricate relationship between the THs variations and the pathological alterations that take place after the ischemic injury.

Thyroid hormone regulates glutamine metabolism and anaplerotic fluxes by inducing mitochondrial glutamate aminotransferase GPT2

Thyroid hormones (THs) are key metabolic regulators coordinating short- and long-term energy needs. In skeletal muscle, THs modulate energy metabolism in pathophysiological conditions. Indeed, hypo- and hyperthyroidism are leading causes of muscle weakness and strength; however, the metabolic pathways underlying these effects are still poorly understood. Using molecular, biochemical, and isotope-tracing approaches combined with mass spectrometry and denervation experiments, we find that THs regulate glutamine metabolism and anaplerotic fluxes by up-regulating the glutamate pyruvate transaminase 2 (GPT2) gene. In humans, GPT2 autosomal recessive mutations cause a neurological syndrome characterized by intellectual disability, microcephaly, and progressive motor symptoms. Here, we demonstrate a role of the TH/GPT2 axis in skeletal muscle in which it regulates muscle weight and fiber diameter in resting and atrophic conditions and results in protection from muscle loss during atrophy. These results describe an anabolic route by which THs rewire glutamine metabolism toward the maintenance of muscle mass.

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THs induce the expression of the mitochondrial GPT2 gene in skeletal muscle

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The GPT2 up-regulation by THs enhances anaplerotic cycles and α-KG production

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GPT2 is reduced during muscle atrophy and is reactivated by THs treatment

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GPT2 KO^+/– mice undergo muscle loss that is partially attenuated by THs

Selective Inhibition of Genomic and Non-Genomic Effects of Thyroid Hormone Regulates Muscle Cell Differentiation and Metabolic Behavior

Thyroid hormones (THs) are key regulators of different biological processes. Their action involves genomic and non-genomic mechanisms, which together mediate the final effects of TH in target tissues. However, the proportion of the two processes and their contribution to the TH-mediated effects are still poorly understood. Skeletal muscle is a classical target tissue for TH, which regulates muscle strength and contraction, as well as energetic metabolism of myofibers. Here we address the different contribution of genomic and non-genomic action of TH in skeletal muscle cells by specifically silencing the deiodinase Dio2 or the β3-Integrin expression via CRISPR/Cas9 technology. We found that myoblast proliferation is inversely regulated by integrin signal and the D2-dependent TH activation. Similarly, inhibition of the nuclear receptor action reduced myoblast proliferation, confirming that genomic action of TH attenuates proliferative rates. Contrarily, genomic and non-genomic signals promote muscle differentiation and the regulation of the redox state. Taken together, our data reveal that integration of genomic and non-genomic signal pathways finely regulates skeletal muscle physiology. These findings not only contribute to the understanding of the mechanisms involved in TH modulation of muscle physiology but also add insight into the interplay between different mechanisms of action of TH in muscle cells.

Thyroid Hormone Enhances Angiogenesis and the Warburg Effect in Squamous Cell Carcinomas

Simple Summary

Cancer cells rewire their metabolism to promote growth, survival, proliferation, and long-term maintenance. Aerobic glycolysis is a prominent trait of many cancers; contextually, glutamine addiction, enhanced glucose uptake and aerobic glycolysis sustain the metabolic needs of rapidly proliferating cancer cells. Thyroid hormone (TH) is a positive regulator of tumor progression and metastatic conversion of squamous cell carcinoma (SCC). Accordingly, overexpression of the TH activating enzyme, D2, is associated with metastatic SCC. The aim of our study was to assess the ability of TH and its activating enzyme in promoting key tracts of cancer progression such as angiogenesis, response to hypoxia and metabolic adaptation. By performing in vivo and in vitro studies, we demonstrate that TH induces VEGF-A in cancer cells and fosters aerobic glycolysis inducing pro-glycolytic mediators, thus implying that TH signal attenuation represents a therapeutic tool to contrast tumor angiogenesis and tumor progression.

Abstract

Cancer angiogenesis is required to support energetic demand and metabolic stress, particularly during conditions of hypoxia. Coupled to neo-vasculogenesis, cancer cells rewire metabolic programs to sustain growth, survival and long-term maintenance. Thyroid hormone (TH) signaling regulates growth and differentiation in a variety of cell types and tissues, thus modulating hyper proliferative processes such as cancer. Herein, we report that TH coordinates a global program of metabolic reprogramming and induces angiogenesis through up-regulation of the VEGF-A gene, which results in the enhanced proliferation of tumor endothelial cells. In vivo conditional depletion of the TH activating enzyme in a mouse model of cutaneous squamous cell carcinoma (SCC) reduces the concentration of TH in the tumoral cells and results in impaired VEGF-A production and attenuated angiogenesis. In addition, we found that TH induces the expression of the glycolytic genes and fosters lactate production, which are key traits of the Warburg effect. Taken together, our results reveal a TH–VEGF-A–HIF1α regulatory axis leading to enhanced angiogenesis and glycolytic flux, which may represent a target for SCC therapy.

The Thyroid Hormone Inactivator Enzyme, Type 3 Deiodinase, Is Essential for Coordination of Keratinocyte Growth and Differentiation

Background: Thyroid hormones (THs) are key regulators of development, tissue differentiation, and maintenance of metabolic balance in virtually every cell of the body. Accordingly, severe alteration of TH action during fetal life leads to permanent deficits in humans. The skin is among the few adult tissues expressing the oncofetal protein type 3 deiodinase (D3), the TH inactivating enzyme. Here, we demonstrate that D3 is dynamically regulated during epidermal ontogenesis. Methods: To investigate the function of D3 in a postdevelopmental context, we used a mouse model of conditional epidermal-specific D3 depletion. Loss of D3 resulted in tissue hypoplasia and enhanced epidermal differentiation in a cell-autonomous manner. Results: Accordingly, wound healing repair and hair follicle cycle were altered in the D3-depleted epidermis. Further, in vitro ablation of D3 in primary culture of keratinocytes indicated that various markers of stratified epithelial layers were upregulated, thereby confirming the pro-differentiative action of D3 depletion and the consequent increased intracellular triiodothyronine levels. Notably, loss of D3 reduced the clearance of systemic TH in vivo, thereby demonstrating the critical requirement for epidermal D3 in the maintenance of TH homeostasis. Conclusion: In conclusion, our results show that the D3 enzyme is a key TH-signaling component in the skin, thereby providing a striking example of a physiological context for deiodinase-mediated TH metabolism, as well as a rationale for therapeutic manipulation of deiodinases in pathophysiological contexts.

Oxidative stress and ERK1/2 phosphorylation as predictors of outcome in hepatocellular carcinoma patients treated with sorafenib plus octreotide LAR

We reported a relevant activity of the combination between sorafenib and octreotide long-acting release (LAR) in advanced hepatocellular carcinoma (HCC) patients. In this work, we have studied if oxidative stress in both serum and peripheral blood mononuclear cells (PBMC) and pERK activation status in PBMC could be predictive of response. In the 20 responsive patients, the decrease of reactive oxygen species levels was already detectable after 10 days (T10) from the beginning of sorafenib administration, and this effect was enhanced by the combined treatment with sorafenib+octreotide LAR (T21). This effect correlated with the modulation of superoxide dismutase (SOD) activity (physiological scavenger of O(2-)) and of serum nitric oxide (NO) levels. Sorafenib alone induced an increase of about 40% of NO levels and of about two-fold of SOD activity in responsive patients, and both effects were significantly potentiated by the combined treatment. We found a gradual reduction of Erk1/2 activity, as evaluated by cytofluorimetric analysis, in 15 responsive patients reaching about 50% maximal decrease at T21. On the other hand, in 17 resistant patients, Erk1/2 activity was about 80% increased at T21. The determination of both the oxidative stress status and pERK activity in PBMC has high value in the prediction of response to sorafenib+octreotide therapy in HCC patients.

Excitatory amino acids in the forebrain of the Naples high-excitability rats: neurochemical and behavioural effects of subchronic D-aspartate and its diethyl ester prodrug

The excitatory amino acids (EAA) L-glutamate (L-Glu), L-aspartate (L-Asp) and D-aspartate (D-Asp) are thought to play a neurotransmitter/neuromodulator role in neuronal communications. Recently, a high level of EAA L-Glu, D- and L-Asp isomers has been found in the forebrain of Naples high-excitability (NHE) rat line that models the mesocortical variant of Attention-Deficit Hyperactivity Disorder (ADHD). The aim of this study was to assess the functions of D-Asp using two forms, i.e. free D-Asp or D-Asp diethyl ester (DEE) as prodrug, on brain and behaviour. Thus, prepuberal rats were given, for two weeks daily, an i.p. injection of D-Asp or DEE or vehicle. Then rats were exposed to two spatial novelties i.e. Làt and radial Olton maze. Behaviour was monitored for indices of activity, non-selective attention (NSA), selective spatial attention (SSA) and emotional reactivity. L-Glu and D- and L-Asp were detected by HPLC in cognitive and non-cognitive brain areas such as prefrontal cortex, striatum, hippocampus and hypothalamus. Results indicate that subchronic D-Asp or DEE (i) reduced EAA levels in the NHE and increased it in the random-bred controls (NRB) rats, (ii) in the Làt-maze D-Asp increased horizontal activity in NHE but DEE decreased it in NRB rats, (iii) in the Olton maze D-Asp and DEE decreased vertical activity in NHE and NRB rats respectively, (iv) D-Asp impaired attention only in NRB decreasing number of arms visited before first repetition. Therefore, data demonstrate differential effects of prepuberal subchronic D-Asp and DEE that may be related to different basal EAA levels in NHE and NRB rats.