Project description:The purpose of this study is to investigate how SREBP1a in macrophages regulates cellular function during muscle regeneration process after injury. We report that the systemic deletion of Srebf1, encoding SREBP1, and macrophage-specific deletion of Srebf1a, encoding SREBP1a, delays the resolution of inflammation, and impairs skeletal muscle regeneration after injury. Srebf1 deficiency impairs mitochondrial function of macrophages and suppresses the accumulation of reparative macrophages to the injured site.
Project description:We studied metabolic angiocrine mechanisms by which endothelial cell_ECs_ can contribute to muscle regeneration from ischemia by using endothelial specific pfkfb3 knockout mice_pfkfb3DEC_ after hind-limb ischemia_HLI_. During muscle regeneration, monocytes are recruited to the injured area and rapidly become macrophages which initially exhibit a more pro-inflammatory M1-like phenotype but soon thereafter functionally repolarize towards an M2-like phenotype to actively support muscle regeneration. Interestingly, macrophages derived from pfkfb3DEC failed to polarized to M2-like macrophages after HLI. Reduced macrophage polarization impairs angiogenesis and muscle regeneration. The RNAseq data are pfkfb3DEC and pfkfb3WT muscle derived macrophages 3 days after HLI.
Project description:IFNγ is traditionally known as a pro-inflammatory cytokine with diverse roles in antimicrobial and antitumor immunity. Yet, findings regarding its sources and functions during the regeneration process following a sterile injury are conflicting. Here, we show that natural killer (NK) cells are the main source of IFNγ in regenerating muscle. Beyond this cell population, IFNγ production is limited to a small population of T cells. We further show that NK cells do not play a major role in muscle regeneration following an acute injury or in dystrophic mice. Surprisingly, the absence of IFNγ per se also has no effect on muscle regeneration following an acute injury. However, the role of IFNγ is partially unmasked when TNFα is also neutralized, suggesting a compensatory mechanism. Using transgenic mice, we showed that conditional inhibition of IFNGR1 signaling in muscle stem cells or fibro-adipogenic progenitors does not play a major role in muscle regeneration. In contrast to common belief, we found that IFNγ is not present in the early inflammatory phase of the regeneration process, but rather peaks when macrophages are acquiring an anti-inflammatory phenotype. Our further transcriptomic analysis suggests that IFNγ cooperates with TNFα to regulate the transition of macrophages from pro- to anti-inflammatory. The absence of the cooperative effect of these cytokines on macrophages, however, does not result in significant regeneration impairment likely due to the presence of other compensatory mechanisms. Our findings support the arising view of IFNγ as a pleiotropic inflammatory regulator rather than an inducer of the inflammatory response.
Project description:IFNγ is traditionally known as a pro-inflammatory cytokine with diverse roles in antimicrobial and antitumor immunity. Yet, findings regarding its sources and functions during the regeneration process following a sterile injury are conflicting. Here, we show that natural killer (NK) cells are the main source of IFNγ in regenerating muscle. Beyond this cell population, IFNγ production is limited to a small population of T cells. We further show that NK cells do not play a major role in muscle regeneration following an acute injury or in dystrophic mice. Surprisingly, the absence of IFNγ per se also has no effect on muscle regeneration following an acute injury. However, the role of IFNγ is partially unmasked when TNFα is also neutralized, suggesting a compensatory mechanism. Using transgenic mice, we showed that conditional inhibition of IFNGR1 signaling in muscle stem cells or fibro-adipogenic progenitors does not play a major role in muscle regeneration. In contrast to common belief, we found that IFNγ is not present in the early inflammatory phase of the regeneration process, but rather peaks when macrophages are acquiring an anti-inflammatory phenotype. Our further transcriptomic analysis suggests that IFNγ cooperates with TNFα to regulate the transition of macrophages from pro- to anti-inflammatory. The absence of the cooperative effect of these cytokines on macrophages, however, does not result in significant regeneration impairment likely due to the presence of other compensatory mechanisms. Our findings support the arising view of IFNγ as a pleiotropic inflammatory regulator rather than an inducer of the inflammatory response.
Project description:MicroRNAs (miRNAs) are important in the regulation of many biological processes including muscle development. However, little is known regarding miRNA regulation of muscle regeneration. In mature murine tibialis anterior muscle following injury, 298 miRNAs were significantly changed during the time course of muscle regeneration including 86 that were altered greater than 10-fold as compared to uninjured muscle. Temporal miRNA expression patterns were identified and included inflammation-related miRNAs (miR-223 and -147) that increased immediately after injury; this pattern contrasted to that of mature muscle-specific miRNAs (miR-1, -133a and -499) that were abruptly decreased following injury and then up-regulated in later regenerative events. Another cluster of miRNAs were transiently increased in the early days of muscle regeneration. This included miR-351, a miRNA that was also transiently expressed during myogenic progenitor cell (MPC) differentiation in vitro. Based on computational predictions, further studies demonstrated that E2f3 was a target of miR-351 in myoblasts. Moreover, knockdown of miR-351 expression inhibited MPC proliferation and promoted apoptosis during MPC differentiation, whereas miR-351 overexpression protected MPC from apoptosis during differentiation. Collectively, these observations suggest that miR-351 is involved in both the maintenance of MPC proliferation and the transition of MPC into differentiated myotubes. Thus, a novel, time-dependent sequence of molecular events during skeletal muscle regeneration has been identified, i.e., miR-351 inhibits E2f3 expression, a key regulator of cell cycle progression and proliferation, and promotes MPC proliferation and protects early differentiating MPC from apoptosis, important events in the hostile tissue environment after acute muscle injury. Skeletal muscles are damaged and repaired repeatedly throughout life. Muscle regeneration maintains locomotor function during aging and delays the appearance of clinical symptoms in neuromuscular diseases, such as Duchenne muscular dystrophy. The capacity for skeletal muscle growth and regeneration is conferred by satellite cells located between the basal lamina and the sarcolemma of mature myofibers. Upon injury, satellite cells reenter the cell cycle, proliferate, and then exit the cell cycle either to renew the quiescent satellite cell pool or to differentiate into mature myofibers. Despite recent advances, genes involved in these processes are still largely unknown. Understanding the molecular mechanisms that regulate satellite cell activities could promote development of novel countermeasures to enhance muscle regeneration that is compromised by diseases or aging. Using a muscle injury mouse model, we profiled miRNA expression during muscle regeneration.
Project description:After injury, muscles require fully functional macrophages to recover completely. During muscle regeneration, macrophages transition from a pro-inflammatory to a pro-restorative phenotype ensures the proper regeneration. Lactate is a crucial molecule for muscle-residing macrophage polarisation. Histone lactylation, a direct derivative of lactate, has been implicated in macrophage polarisation in vitro . In this work, we show for the first time that macrophages recruited to the muscle after ischemic injury modify their histone lactylome between 2 and 4 days post injury. Absolute histone lactylation levels increase significantly. Although subtly, also the genomic enrichment of H3K18la changes from 2 to 4 days post injury and this correlates with gene expression changes. Interestingly, we find that H3K18la genomic enrichment changes from day 2 to day 4 post injury are predictive for gene expression changes later in time, from day 4 to day 7, rather than being a reflection of past gene expression changes from day 1 to day 2. Our results suggest that histone lactylation dynamics are functionally important for the resolving action of macrophages during muscle regeneration.