Identification of Sulfs as therapeutic targets for the treatment of age-impaired skeletal muscle regeneration

描述(申请人提供)：衰老不可避免地与干细胞再生能力减弱有关。我们选择骨骼肌作为模型系统，研究衰老环境对干细胞功能影响的调控机制。衰老的骨骼肌降低了FGF2的水平，升高了WNTS和TGF2的水平，导致常驻干细胞(即所谓的卫星细胞)的增殖减少，并在再生过程中增加了纤维化。FGF2、WNTS和TGF2的生物利用度受硫酸乙酰肝素的调节。这项建议研究了在骨骼肌再生过程中调节年龄相关环境信号向卫星细胞传输的依赖于乙酰肝素的机制。第一组实验集中于两个细胞外硫酸乙酰肝素6-O-内硫酸酯酶(Sulf)在年龄相关信号生物利用度的不同调节中的作用。Sulf酶促硫酸乙酰肝素6-O-硫化，从而减少WNTS和TGF2与肝素硫酸盐的结合，同时破坏FGF2与受体的相互作用。因此，Sulf被认为促进了年龄增加的Wnt和TGF2信号，同时抑制了年龄减少的FGF2信号，导致卫星细胞功能受损。这一假说将通过结合体内再生和体外培养试验在老年对照组、全身和卫星细胞特异性Sulf双突变小鼠中比较肌肉发生、纤维化和年龄相关再生信号的效率来验证。第二组实验将测试在结构和信号功能上与硫缺乏小鼠的硫酸肝素相似的肝素是否会提高衰老环境中骨骼肌再生的效率。这些研究的结果有望导致硫酸盐和乙酰肝素依赖的机制的发现，这些机制调节卫星细胞和衰老的肌肉环境之间的信号交流。这些知识可能会为预防和治疗因年龄而受损的肌肉再生开辟新的途径。

DESCRIPTION (provided by applicant): Aging is inevitably associated with diminished regeneration capacity of stem cells. We choose the skeletal muscle as a model system to study mechanisms that regulate the influence from aged environment on stem cell function. Aged skeletal muscle has reduced levels of FGF2 and elevated Wnts and TGF2, leading to decreased proliferation of resident stem cells (so called satellite cells) and increased fibrosis during regeneration. The bioavailability of FGF2, Wnts and TGF2 is regulated by sulfated heparan sulfate. This proposal investigates heparan sulfate-dependent mechanisms that regulate the transmission of age-related environmental signals to satellite cells during skeletal muscle regeneration. The first set of experiments focuses on roles of two extracellular heparan sulfate 6-O-endosulfatases (Sulfs) in differential regulation of the bioavailability of age-related signals. Sulfs enzymatically remodel heparan sulfate 6-O-sulfation, thereby Sulfs reduce Wnts and TGF2 binding to heparan sulfate, while disrupting FGF2 interaction with the receptor. Therefore, Sulfs are hypothesized to promote age-augmented Wnt and TGF2 signaling, while repressing age-reduced FGF2 signaling, leading to impaired function of satellite cells. This hypothesis will be tested by comparing the efficiency of myogenesis, fibrosis and age-related regeneration signaling in aged control, systemic and satellite cell-specific Sulf double mutant mice using a combination of in vivo regeneration and in vitro culture assays. The second set of experiments will test whether heparin, which is similar to heparan sulfate of Sulf-deficient mice in the structure and signaling function, will improve the efficiency of skeletal muscle regeneration in an aged environment. The results of these investigations are expected to lead to the discovery of Sulf- and heparan sulfate-dependent mechanisms that regulate signal communication between satellite cells and the aged muscle environment. Such knowledge may open new venues for prevention and therapy of impaired muscle regeneration by age.