Sphingolipid metabolism controls mammalian heart regeneration.

Utilization of lipids as energy substrates after birth causes cardiomyocyte (CM) cell-cycle arrest and loss of regenerative capacity in mammalian hearts. Beyond energy provision, proper management of lipid composition is crucial for cellular and organismal health, but its role in heart regeneration remains unclear. Here, we demonstrate widespread sphingolipid metabolism remodeling in neonatal hearts after injury and find that SphK1 and SphK2, isoenzymes producing the same sphingolipid metabolite sphingosine-1-phosphate (S1P), differently regulate cardiac regeneration. SphK2 is downregulated during heart development and determines CM proliferation via nuclear S1P-dependent modulation of histone acetylation. Reactivation of SphK2 induces adult CM cell-cycle re-entry and cytokinesis, thereby enhancing regeneration. Conversely, SphK1 is upregulated during development and promotes fibrosis through an S1P autocrine mechanism in cardiac fibroblasts. By fine-tuning the activity of each SphK isoform, we develop a therapy that simultaneously promotes myocardial repair and restricts fibrotic scarring to regenerate the infarcted adult hearts.

Sodium alginate/sodium lignosulfonate hydrogel based on inert Ca2+ activation for water conservation and growth promotion.

Soil degradation has become a major global problem owing to the rapid development of agriculture. The problems of soil drought and decreased soil fertility caused by soil degradation severely affect the development of the agricultural and forestry industries. In this study, we designed sodium alginate (SA)/sodium lignosulfonate (SLS) hydrogel based on the activation and crosslinking of inert Ca2+. CaCO3 and SA were mixed, and then, inert Ca2+ was activated to prepare a gel with a stable structure and a uniform interior and exterior. The crosslinking activated by inert Ca2+ enhanced the stability of the hydrogel, and the optimal swelling rate of the hydrogel reached 28.91 g/g, thereby effectively improving the water-holding capacity of the soil (77.6-108.83 g/kg). SLS was degraded into humic acid (HA) and gradually released, demonstrating a positive growth-promoting effect in plant growth experiments. The SA/SLS hydrogel can be used for soil water retention and mitigation to significantly decrease the water loss rate of soil. This study will assist in addressing soil drought and fertility loss.

Experimental study on shear strength of saturated remolded loess.

Loess has the characteristics of large porosity, loose structure, uniform composition and strong collapsibility. When encountering heavy rainfall and irrigation prone to saturation, resulting in loess landslides, roadbed subsidence and dam instability. In order to study the effect of dry density and shear rate on the shear strength of saturated remolded loess, the consolidated undrained (CU) test was carried out in Yan'an City by using SLB-6A stress-strain controlled triaxial shear permeability test instrument. The shear rate, confining pressure and dry density were controlled during the test. The dry densities of the samples were 1.5 g / cm3, 1.6 g / cm3 and 1.7 g / cm3, respectively. CU tests of saturated remolded loess were carried out at different shear rates under the confining pressures of 100 kPa, 150 kPa and 200 kPa, respectively. It is found that the stress-strain curve of saturated remolded loess gradually moves upward with the increase of dry density. With the increase of dry density, the cohesion and internal friction angle of remolded saturated loess samples increase. At the same shear rate, with the increase of dry density, the deviatoric stress of the specimen increases significantly.

Tunnel failure mechanism during loading and unloading processes through physical model testing and DEM simulation.

Geo-materials may present varying mechanical properties under different stress paths, especially for tunnel excavation, which is typically characterized by the decreased radial stress and increased axial stress during the complex loading and unloading process. This study carried out a comparative analysis between the loading and unloading model testing, which was then combined with PFC2D simulation, aiming to reveal the fracture propagation pattern, microscopic stress and force chain distribution of the rock mass surrounding the tunnel. Comparisons of extents and development of tensile strain between loading and unloading testing results were made. The overall stability, the integrity of rock mass, and the failure pattern transition under loading and unloading processes were systematically examined. In addition, for the two unloading cases with different vertical stresses imposed, the failure patterns were both identified as the collapse of the V - shaped extruded sidewall, due to the coupling of the shear failure and the vertical tensile failure in the sidewall wedge.