Cellular and Transcriptional Dynamics during Brown Adipose Tissue Regeneration under Acute Injury

Brown adipose tissue(BAT)is the major site of non-shivering thermogenesis and crucial for systemic metabolism.Under chronic cold exposures and high-fat diet challenges,BAT undergoes robust remodeling to adapt to physiological demands.However,whether and how BAT regenerates after acute injuries are poorly understood.Here,we established a novel BAT injury and regeneration model(BAT-IR)in mice and performed single-cell RNA sequencing(scRNA-seq)and bulk RNA-seq to determine cellular and transcriptomic dynamics during BAT-IR.We further defined distinct fibro-adipogenic and myeloid progenitor populations contributing to BAT regeneration.Cell trajectory and gene expression analyses uncovered the involvement of MAPK,Wnt,and Hedgehog(Hh)signaling pathways in BAT regeneration.We confirmed the role of Hh signaling in BAT development through Myf5Cre-mediated conditional knockout(cKO)of the Sufu gene to activate Hh signaling in BAT and muscle progenitors.Our BAT-IR model therefore provides a paradigm to identify conserved cellular and molecular mechanisms underlying BAT development and remodeling.

Biomimetic glycosaminoglycan-based scaffolds improve skeletal muscle regeneration in a Murine volumetric muscle loss model

Volumetric muscle loss(VML)injuries characterized by critical loss of skeletal muscle tissues result in severe functional impairment.Current treatments involving use of muscle grafts are limited by tissue availability and donor site morbidity.In this study,we designed and synthesized an implantable glycosaminoglycan-based hydrogel system consisting of thiolated hyaluronic acid(HA)and thiolated chondroitin sulfate(CS)cross-linked with poly(ethylene glycol)diacrylate to promote skeletal muscle regeneration of VML injuries in mice.The HA-CS hydrogels were optimized with suitable biophysical properties by fine-tuning degree of thiol group substitution to support C2C12 myoblast proliferation,myogenic differentiation and expression of myogenic markers MyoD,MyoG and MYH8.Furthermore,in vivo studies using a murine quadriceps VML model demonstrated that the HA-CS hydrogels supported integration of implants with the surrounding host tissue and facilitated migration of Pax7+satellite cells,de novo myofiber formation,angiogenesis,and innervation with minimized scar tissue formation during 4-week implantation.The hydrogel-treated and autograft-treated mice showed similar functional improvements in treadmill performance as early as 1-week post-implantation compared to the untreated groups.Taken together,our results demonstrate the promise of HA-CS hydrogels as regenerative engineering matrices to accelerate healing of skeletal muscle injuries.

Chchd10 is dispensable for myogenesis but critical for adipose browning

The Chchd10 gene encodes a coiled-coil-helix-coiled-coil-helix-domain containing protein predicted to function in the mitochondrion and nucleus.Mutations of Chchd10 are associated with ALS,dementia and myopathy in humans and animal models,but how knockout of Chchd10(Chchd10KO)affects various tissues especially skeletal muscle and adipose tissues remains unclear.Here we show that Chchd10 expression increases as myoblasts and preadipocytes dif-ferentiate.During myogenesis,CHCHD10 interacts with TAR DNA binding protein 43(TDP-43)in regenerating myofib-ers in vivo and in newly differentiated myotubes ex vivo.Surprisingly,Chchd10KO mice had normal skeletal muscle development,growth and regeneration,with moderate defects in grip strength and motor performance.Chchd10KO similarly had no effects on development of brown and white adipose tissues(WAT).However,Chchd10KO mice had blunted response to acute cold and attenuated cold-induced browning of WAT,with markedly reduced UCP1 levels.Together,these results demonstrate that Chchd10 is dispensable for normal myogenesis and adipogenesis but is required for normal motility and cold-induced,mitochondrion-dependent browning of adipocytes.The data also sug-gest that human CHCHD10 mutations cause myopathy through a gain-of-function mechanism.