New Insights into the Lactate Shuttle: Role of MCT4 in the Modulation of the Exercise Capacity.

Lactate produced by muscle during high-intensity activity is an important end product of glycolysis that supports whole body metabolism. The lactate shuttle model suggested that lactate produced by glycolytic muscle fibers is utilized by oxidative fibers. MCT4 is a proton coupled monocarboxylate transporter preferentially expressed in glycolytic muscle fibers and facilitates the lactate efflux. Here we investigated the exercise capacity of mice with disrupted lactate shuttle due to global deletion of MCT4 (MCT4−/−) or muscle-specific deletion of the accessory protein Basigin (iMSBsg−/−). Although MCT4−/− and iMSBsg−/− mice have normal muscle morphology and contractility, only MCT4−/− mice exhibit an exercise intolerant phenotype. In vivo measurements of compound muscle action potentials showed a decrement in the evoked response in the MCT4−/− mice. This was accompanied by a significant structural degeneration of the neuromuscular junctions (NMJs). We propose that disruption of the lactate shuttle impacts motor function and destabilizes the motor unit

Cyclin D1 Restrains Oncogene-Induced Autophagy by Regulating the AMPK-LKB1 Signaling Axis.

Autophagy activated after DNA damage or other stresses mitigates cellular damage by removing damaged proteins, lipids, and organelles. Activation of the master metabolic kinase AMPK enhances autophagy. Here we report that cyclin D1 restrains autophagy by modulating the activation of AMPK. In cell models of human breast cancer or in a cyclin D1-deficient model, we observed a cyclin D1-mediated reduction in AMPK activation. Mechanistic investigations showed that cyclin D1 inhibited mitochondrial function, promoted glycolysis, and reduced activation of AMPK (pT172), possibly through a mechanism that involves cyclin D1-Cdk4/Cdk6 phosphorylation of LKB1. Our findings suggest how AMPK activation by cyclin D1 may couple cell proliferation to energy homeostasis

Monocarboxylate Transporter 4 (MCT4) Knockout Mice Have Attenuated 4NQO Induced Carcinogenesis; A Role for MCT4 in Driving Oral Squamous Cell Cancer

Head and neck squamous cell carcinoma (HNSCC) is the 6th most common human cancer and affects approximately 50,000 new patients every year in the US. The major risk factors for HNSCC are tobacco and alcohol consumption as well as oncogenic HPV infections. Despite advances in therapy, the overall survival rate for all-comers is only 50%. Understanding the biology of HNSCC is crucial to identifying new biomarkers, implementing early diagnostic approaches and developing novel therapies. As in several other cancers, HNSCC expresses elevated levels of MCT4, a member of the SLC16 family of monocarboxylate transporters. MCT4 is a H+-linked lactate transporter which functions to facilitate lactate efflux from highly glycolytic cells. High MCT4 levels in HNSCC have been associated with poor prognosis, but the role of MCT4 in the development and progression of this cancer is still poorly understood. In this study, we used 4-nitroquinoline-1-oxide (4NQO) to induce oral cancer in MCT4−/− and wild type littermates, recapitulating the disease progression in humans. Histological analysis of mouse tongues after 23 weeks of 4NQO treatment showed that MCT4−/− mice developed significantly fewer and less extended invasive lesions than wild type. In mice, as in human samples, MCT4 was not expressed in normal oral mucosa but was detected in the transformed epithelium. In the 4NQO treated mice we detected MCT4 in foci of the basal layer undergoing transformation, and progressively in areas of carcinoma in situ and invasive carcinomas. Moreover, we found MCT4 positive macrophages within the tumor and in the stroma surrounding the lesions in both human samples of HNSCC and in the 4NQO treated animals. The results of our studies showed that MCT4 could be used as an early diagnostic biomarker of HNSCC. Our finding with the MCT4−/− mice suggest MCT4 is a driver of progression to oral squamous cell cancer and MCT4 inhibitors could have clinical benefits for preventing invasive HNSCC

Lactate efflux from intervertebral disc cells is required for maintenance of spine health.

Maintenance of glycolytic metabolism is postulated to be required for health of the spinal column. In the hypoxic tissues of the intervertebral disc and glycolytic cells of vertebral bone, glucose is metabolized into pyruvate for ATP generation and reduced to lactate to sustain redox balance. The rise in intracellular H+ /lactate concentrations are balanced by plasma-membrane monocarboxylate transporters (MCTs). Using MCT4 null mice and human tissue samples, complimented with genetic and metabolic approaches, we determine that H+ /lactate efflux is critical for maintenance of disc and vertebral bone health. Mechanistically, MCT4 maintains glycolytic and TCA cycle flux and intracellular pH homeostasis in the nucleus pulposus compartment of the disc, where HIF-1α directly activates an intronic enhancer in SLC16A3. Ultimately, our results provide support for research into lactate as a diagnostic biomarker for chronic, painful disc degeneration

New Insights into the Lactate Shuttle: Lesson Learned from the MCT4 Knock Out Mouse

For a long time, lactate has been considered just a waste by-product of anaerobic glycolysis and cause of muscle fatigue after intense exercise. Extensive research, however, showed that lactate is a physiological product of both aerobic and anaerobic glycolysis and its metabolism is much more complex, as it can serve both as energy substrate and signaling molecule. In 1986 George Brooks proposed that during exercise, lactate is shuttled from fast-twitch fibers to slow-twitch ones, as well as other tissue like heart and brain, where it is metabolized through oxidative phosphorylation. The flux of lactate is facilitated by the Monocarboxylate Transporters (MCT), H+-coupled transporters found at the plasma membrane of several tissues. MCT1 and MCT4 mediate the influx and efflux of lactate in slow twitch and fast twitch muscle respectively. Besides their role in maintaining the physiological concentrations of lactate and other metabolites, MCT1 and MCT4 have a relevant role in several pathologies including cancer and inflammation, as well as neurodegenerative diseases. In the first of the presented studies, we investigated the importance of the lactate shuttle during exercise by using whole-body (MCT4-/-) and muscle-specific BSG knockout mice. Using a combination of in vivo and ex vivo functional assays, we found that MCT4-/- mice are exercise intolerant. However, the disruption of the lactate flux does not affect the morphological and intrinsic contractile properties of muscle. To understand the causes of the limited exercise capacity in the MCT4-/- mice, we investigated the role of MCT4 in the neuronal components of the motor unit. Although we detected MCT4 expression in the lumbar spinal cord, the deletion in the MCT4-/- mice did not cause any morphological changes to the motoneurons or the sciatic nerve. Morphological analysis of the neuromuscular junctions (NMJs) showed a significant age-dependent, pre- and post-synaptic degeneration in the fast EDL muscles (but not in the slow, soleus) from MCT4-/- mice. Consistently, in vivo analysis of compound muscle action potentials (CMAPs) in control and MCT4-/- mice showed a significant reduction of the electromyographic (EMG) signal amplitude indicative of functional impairment of the propagation of action potentials. In conclusion, this first study showed that, while well-tolerated in muscle, the ablation of MCT4 causes significant age-dependent alterations of stability and function of the motor unit and in particular of the NMJs. As mentioned, the metabolic and signaling effects of MCT4 are relevant for a variety of metabolically active tissues such as exercising muscle, and also cancer cells. Indeed, MCT4 expression is significantly high in several type of cancers,and is associated with poor prognosis. In the second study presented here, we investigated the consequences of MCT4 ablation in a model carcinogen-induced head and neck squamous cell cancer (HNSCC). We found that MCT4-/- mice developed fewer and less severe tumor lesions compared to the control animals. We showed that MCT4 is expressed in small foci of early lesions. In more severe lesions, like in situ carcinomas, it was found in the hypoxic core of the tumors. Widespread expression of the transporter in both tumor cells and stroma was found in invasive lesions. Moreover, we detected MCT4 positive macrophages infiltrating the tumors and in the adjacent stroma, suggesting that the lactate transporter plays a role in immune activation and tumor progression. This was confirmed also in samples of human HNSCC. The result of this study showed that MCT4 is a potential new marker for early HNSCC lesions and the inhibition of lactate efflux could have a clinical benefit for the prevention of invasive tumors. Overall, the study of the MCT4-/- mice allowed us to better understand the physiological role of the lactate transporter in metabolically active tissues, providing new evidence supporting the potential applicability of MCT4 inhibitors for the treatment of pathologies such cancer

Chinese language Law Corpus (#ChinLaC)

The Chinese language Law Corpus (#ChinLaC) is a diachronic corpus of Chinese laws and regulations from the ’50s to present days. It consists of more than 400 texts covering the codes and the legislative texts of the People’s Republic of China and Taiwan, including some randomly selected amendments of these. It aims to be representative of the modern Chinese legal language as a textual genre. Texts were collected from institutional and governmental repositories. Each text has been saved in .txt format so to make it readable by commonly used software tools for corpus analysis, such as Sketch Engine, AntConc, and #LancsBox. The corpus comes with a metadata file, whereby each file has been coded for language, territorial entity, implementation, and amendment dates

Corpus of Chinese language International Relations (#ChInRel)

The corpus of Chinese language International Relations (#ChInRel) is a diachronic corpus of texts from the ’50s to present days relating to the international relations of Chinese-speaking territorial entities (Sinosphere). It consists of more than 400 texts covering international laws and regulations (e.g., treaties) as well as political speeches delivered in front of or in connection to an international audience. It aims to be representative of Mandarin official texts of international relevance as a textual genre. Texts were collected from institutional and governmental repositories. Each text has been saved in .txt format so to make it readable by commonly used software tools for corpus analysis such as Sketch Engine, AntConc, and #LancsBox. The corpus comes with a metadata file whereby each file has been coded for language, territorial entity, signature and amendment dates

A cellular hierarchy of Notch and Kras signaling controls cell fate specification in the developing mouse salivary gland

The development of the mouse salivary gland involves a tip-driven process of branching morphogenesis that takes place in concert with differentiation into acinar, myoepithelial, and ductal (basal and luminal) sub -line-ages. By combining clonal lineage tracing with a three-dimensional (3D) reconstruction of the branched epithelial network and single-cell RNA-seq analysis, we show that in tips, a heterogeneous population of re-newing progenitors transition from a Krt14+ multipotent state to unipotent states via two transcriptionally distinct bipotent states, one restricted to the Krt14+ basal and myoepithelial lineage and the other to the Krt8+ acinar and luminal lineage. Using genetic perturbations, we show how the differential expression of Notch signaling correlates with spatial segregation, exits from multipotency, and promotes the Krt8+ lineage, whereas Kras activation promotes proacinar fate. These findings provide a mechanistic basis for how posi-tional cues within growing tips regulate the process of lineage segregation and ductal patterning.11Nsciescopu