Profiling age-related muscle weakness and wasting: neuromuscular junction transmission as a driver of age-related physical decline
Physiological changes that lead to skeletal muscle dysfunction and atrophy during aging are poorly understood and thus therapeutic interventions which
Disparate bone anabolic cues activate bone formation by regulating the rapid lysosomal degradation of sclerostin protein
Sclerostin is an osteocyte-derived glycoprotein with an inhibitory role in bone formation. Deletion of the Sost gene, which controls sclerostin protein expression, has been shown to increase bone mass in mice. As such, sclerostin shows therapeutic potential in treating bone mass conditions such as osteoporosis. This study focuses on elucidating the molecular control of this protein in both in vitro and in vivo settings. Cell lines Ocy454 and UMR106 were first subjected to fluid shear stress-mediated bone mechanical loading. This resulted in a loss of sclerostin protein abundance. An in vivo assessment was then conducted where mice were subjected to ulnar loads using Aurora’s 305C Dual-Mode lever system. Ulnae were harvested post-load and osteocytes were assessed, showing reduced sclerostin abundance compared to limbs without loading. A previous study showed that NOX2-mediated ROS is an essential part of the mechano-transduction pathway involving sclerostin protein loss. To confirm these findings in a whole animal analysis, the authors analyzed the effect of ulnar loading on mice pre-treated with apocynin, a NOX2 inhibitor. The findings showed that apocynin prevented bone formation that was otherwise load-induced. Therefore, NOX2 ROS was found to be necessary for sclerostin degradation as inhibition of NOX2 lessened the degradation of sclerostin. Furthermore, it was found that inhibition of lysosomal degradation reduced sclerostin protein degradation. These results suggest that inhibiting NOX2 or lysosomal function prevents load-induced sclerostin degradation and subsequent bone formation. The authors then analyzed induced pluripotent stem cell (iPSC)-derived osteoblasts from patients with Gaucher disease, a disease categorized as a lysosomal storage disorder. This analysis showed a significant increase in levels of sclerostin compared to iPSC-derived osteoblasts from patients without Gaucher disease. It was also found that treating Gaucher iPSC-derived osteoblasts with an enzyme restoring lysosomal function resulted in a decrease in sclerostin. These data provide insights into the molecular regulation of osteocyte sclerostin protein and shed light on potential therapeutic targets in the treatment of bone-related conditions.
Influence of external forces on actin-dependent T cell protrusions during immune synapse formation
T-cell activation is necessary for producing an adaptive immune response. For T-cell activation to occur, an antigen-presenting cell (APC) must make direct contact with it. This contact region has been shown to control many T-cell functions, and it is from this contact point that protrusions have been observed. To further characterize these protrusions, this study investigated the effect of various APC-mimicking forces on protrusion dynamics. To mimic APC-induced T-cell activation, a micropipette force probe attached to an activating microbead was used. To evaluate micropipette flexibility, the bending stiffness was measured against a microindenter calibrated with Aurora’s 406A force probe. T-cell activation was induced once the microbead would make contact with the cell at a desired compressive or pulling force. To determine if protrusion was affected by external forces produced by APCs during activation, protrusion lengths were monitored following the application of various forces. It was found that the higher the compressive force, the shorter the protrusion was. Conversely, the larger the absolute pulling force was, the longer the protrusion grew. It was also observed longer protrusions were smaller in diameter, at all forces. To determine whether protrusion dynamics were affected by Arp2/3, a protein complex regulating actin polymerization, T-cells were treated with an Arp2/3-specific inhibitor. Not only were protrusion maximum lengths reduced following treatment, but they began growth later in time and at slower speeds. Finally, confocal imaging was used to assess F actin localization within protrusions. The results showed that the walls were rich with F actin whereas the center was depleted. A similar analysis of T cells and model APCs showed the same F actin localization. This study suggests that protrusion growth is set by an intracellular constant time and that protrusion dynamics are influenced by external forces. In addition to this, actin assembly within protrusions is facilitated by the Arp2/3 complex.