The ESCRT-0 subcomplex component Hrs/Hgs is a master regulator of myogenesis via modulation of signaling and degradation pathways

Background

Myogenesis is a highly regulated process ending with the formation of myotubes, the precursors of skeletal muscle fibers. Differentiation of myoblasts into myotubes is controlled by myogenic regulatory factors (MRFs) that act as terminal effectors of signaling cascades involved in the temporal and spatial regulation of muscle development. Such signaling cascades converge and are controlled at the level of intracellular trafficking, but the mechanisms by which myogenesis is regulated by the endosomal machinery and trafficking is largely unexplored. The Endosomal Sorting Complex Required for Transport (ESCRT) machinery composed of four complexes ESCRT-0 to ESCRT-III regulates the biogenesis and trafficking of endosomes as well as the associated signaling and degradation pathways. Here, we investigate its role in regulating myogenesis.

Results

We uncovered a new function of the ESCRT-0 hepatocyte growth factor-regulated tyrosine kinase substrate Hrs/Hgs component in the regulation of myogenesis. Hrs depletion strongly impairs the differentiation of murine and human myoblasts. In the C2C12 murine myogenic cell line, inhibition of differentiation was attributed to impaired MRF in the early steps of differentiation. This alteration is associated with an upregulation of the MEK/ERK signaling pathway and a downregulation of the Akt2 signaling both leading to the inhibition of differentiation. The myogenic repressors FOXO1 as well as GSK3β were also found to be both activated when Hrs was absent. Inhibition of the MEK/ERK pathway or of GSK3β by the U0126 or azakenpaullone compounds respectively significantly restores the impaired differentiation observed in Hrs-depleted cells. In addition, functional autophagy that is required for myogenesis was also found to be strongly inhibited.

Conclusions

We show for the first time that Hrs/Hgs is a master regulator that modulates myogenesis at different levels through the control of trafficking, signaling, and degradation pathways.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01091-4.

Treatment of As-rich mine effluents and produced residues stability: Current knowledge and research priorities for gold mining

Refractory ores, in which gold is often embedded within As-bearing and acid-generating sulfide minerals, are becoming the main gold source worldwide. These ores require an oxidizing pre-treatment, prior to cyanidation, to efficiently breakdown the sulfides and enhance gold liberation. As a result, large volumes of As-rich effluents (> 500 mg/L) are produced through the pre-oxidation of refractory gold ores and/or the exposure of As-bearing tailings upon exposure to air and water. Limited information is available on performant treatment of these effluents, especially of pre-oxidation effluents characterized by a complex chemistry, extremely acidic or alkaline pH and high concentrations of arsenic. The treatment of As-rich effluents is mainly based on precipitation (using Al or Fe salts and/or Ca-based compounds) and (electro)-chemical or biological oxidation processes. A performant treatment process must maximize As removal from contaminated mine water and allow for the production of residues that are geochemically stable over the long term. An extensive literature review showed that Fe(III)-As(V) precipitates, especially bioscorodite and (nano)scorodite, appear to be the most appropriate forms to immobilize As due to their low solubility and high stability, especially when encapsulated within an inert material such as hydroxyl gels. Research is still required to assess the long-term stability of these As-bearing residues under mine-site conditions for the sustainable exploitation of refractory gold deposits.

Characterization of Kef Shfeir phosphate sludge (Gafsa, Tunisia) and optimization of its dewatering

Water separation and recovery through thickening require adapted flocculants and densification processes. This study aimed to maximize water recovery from phosphate sludge (PS) at Kef Shfeir mine operation, Gafsa Phosphate Company, Tunisia. Representative samples of PS, PS treated with flocculant (F-PS), raw water, and recycled water were collected on the mine site. Solid samples (PS and F-PS) were characterized physically, chemically and mineralogically. To maximize water recovery, thickening tests were performed on the PS using different flocculants to optimize flocculant concentration, the agitation speed and the settling time. Results showed that PS had positive surface charge since its paste pH (7.3) was lower than pH_PZC (8.0), whereas the tested flocculant (Slim Floc used by the company) showed negative surface charge. Solid samples contained coarse medium and fine particles of carbonates, silicates and residual hydroxyapatite. The cumulative fractions +32 μm of PS contained a promising residual potential of fluorapatite (up to 39.2%). Water recovery was about 58.1%, when the anionic Slim Floc was used, for a consumption rate of 1200 g/t of dry solids. Best efficiency (84%) of water recovery was obtained with the anionic flocculant E24 for a consumption rate of 360 g/t of dry solids, which is 3 times lower than actual flocculant consumption.

Determination of critical operational conditions favoring sulfide production from domestic wastewater treated by a sulfur-utilizing denitrification process

The aim of this study was to determine the critical operational conditions leading to the generation of sulfide in a domestic wastewater treated by a sulfur-utilizing denitrification process. The influence of various important parameters on the reduction of the sulfates present in denitrified domestic wastewaters to sulfide was studied. Experiments were carried out in batch mode with denitrified domestic wastewaters containing various amounts of both organic matter and sulfates. Preliminary results showed that aqueous sulfide was generated for DOC and sulfate contents higher than 56 mg/L and 371 mg/L, respectively, while DOC and sulfate contents of 77 mg/L and 412 mg/L, respectively, were required to allow the release of gaseous H₂S. Good correlations were also observed between gaseous sulfide production and the values of ORP and DOC, while the amounts of dissolved sulfide produced seemed to be correlated with the ORP values and the concentration of sulfates. Additional experiments were conducted using a Box-Behnken methodology to determine if the production of aqueous or gaseous sulfide can be predicted depending on the DOC (from 50 to 90 mg/L) and sulfate contents (from 160 to 380 mg/L) at various temperatures ranging from 5 to 25 °C. The highest sulfide generation (H₂S_(g) = 84.8 ppm and H₂S_(aq) = 2.42 mg/L) occurred at 25 °C with DOC and sulfate concentrations starting from 90 mg/L and 270 mg/L, respectively, indicating that the production of sulfides from denitrified domestic wastewaters required conditions not likely to occur at the effluent of a sulfur-based denitrification unit following secondary treatment.

Assessment of sulfide production risk in soil during the infiltration of domestic wastewater treated by a sulfur-utilizing denitrification process

This study aimed to determine the potential of sulfide generation during infiltration through soil of domestic wastewater treated by a sulfur-utilizing denitrification process. Three types of soil with different permeability rates (K s = 0.028, 0.0013, and 0.00015 cm/s) were investigated to evaluate the potential risk of sulfur generation during the infiltration of domestic wastewater treated by a sulfur-utilizing denitrification system. These soils were thoroughly characterized and tested to assess their capacity to be used as drainages for wastewaters. Experiments were conducted under two operating modes (saturated and unsaturated). Sulfate, sulfide, and chemical oxygen demand (COD) levels were determined over a period of 100 days. Despite the high concentration of sulfates (200 mg/L) under anaerobic conditions (ORP = -297 mV), no significant amount of sulfide was generated in the aqueous (<0.2 mg/L) or gaseous (<0.15 ppm) phases. Furthermore, the soil permeability did not have a noticeable effect on the infiltration of domestic wastewater treated by a sulfur-utilizing denitrification system due to low contents of organic matter (i.e., dissolved organic carbon, DOC). The autotrophic denitrification process used to treat the domestic wastewater allowed the reduction of the concentration of biochemical oxygen demand (BOD5) below 5 mg/L, of DOC below 7 mg/L, and of COD below 100 mg/L.