Urokinase-type plasminogen activator increases hepatocyte growth factor activity required for skeletal muscle regeneration

Abstract

The plasminogen system plays a crucial role in the repair of a variety of tissues, including skeletal muscle. We hypothesized that urokinase-type plasminogen activator (uPA) promotes muscle regeneration by activating hepatocyte growth factor (HGF), which, in turn, stimulates proliferation of myoblasts required for regeneration. In our studies, levels of active HGF and phosphorylation of the HGF receptor c-met were increased after muscle injury in wild-type mice. Compared with wild-type animals, mice deficient in uPA (uPA ؊/؊ ) had markedly reduced HGF levels and c-met activation after muscle damage. This reduced HGF activity in uPA ؊/؊ animals was associated with decreased cell proliferation, myoblast accumulation, and new muscle fiber formation. On the other hand, HGF activity was enhanced at early time points in PAI-1 ؊/؊ mice compared with wild-type mice and the PAI-1 ؊/؊ animals exhibited accelerated muscle fiber regeneration. Furthermore, administration of exogenous uPA rescued HGF levels and muscle regeneration in uPA ؊/؊ mice, and an HGF-blocking antibody reduced HGF activity and muscle regeneration in wildtype mice. We also found that uPA promotes myoblast proliferation in vitro through its proteolytic activity, and this process was inhibited by an HGFblocking antibody. Together, our findings demonstrate that uPA promotes muscle regeneration through HGF activation and subsequent myoblast proliferation. IntroductionThe plasminogen system plays a crucial role in the repair of a variety of tissues. This extracellular serine protease cascade includes the urokinase-type plasminogen activator (uPA) and its primary inhibitor, plasminogen activator inhibitor-1 (PAI-1). The classic function of uPA is to cleave plasminogen to form active plasmin, a broad-spectrum protease with activity toward a variety of extracellular matrix molecules. 1,2 Genetic manipulations that inhibit plasminogen activation lead to impaired healing of lung, liver, kidney, and skin. [3][4][5][6] Similarly, mice deficient in uPA or plasminogen demonstrate markedly impaired muscle regeneration. [7][8][9] In contrast, mice lacking PAI-1 exhibit accelerated muscle regeneration. 7 Despite its robust effect on skeletal muscle regeneration, the molecular mechanisms by which the plasminogen system regulates this process remain largely undefined. Clearance of the provisional fibrin matrix that is deposited after muscle injury may be one mechanism by which uPA promotes regeneration. 8 However, uPA may also promote tissue repair through other pathways, such as the proteolytic activation of growth factors, including hepatocyte growth factor (HGF). HGF is synthesized and secreted as an inactive single-chain molecule, and proteolytic cleavage results in formation of the active 2-chain form, which has affinity for the c-met receptor. [10][11][12] uPA is one of a select group of proteases known to activate HGF, 11,12 the others being tissue-type plasminogen activator, factor XIa, factor XIIa, matriptase, and HGF activator. [13][14][15] In addition, uPA app...

Urokinase plasminogen activator and receptor promote collagen-induced arthritis through expression in hematopoietic cells

“…uPA has been shown to support macrophage migration/chemotaxis in vitro as well as in animal models of atherosclerosis, skeletal muscle regeneration, and cancer. [52][53][54] uPA/uPAR may modulate proinflammatory CIA effector cell functions in concert with integrins or other cell-surface receptors. [55][56][57] It has also been proposed that uPA may be driving arthritis pathogenesis by supporting immune complex-mediated complement factor C5a activation and inflammation.…”

Interleukin-17 modulates myoblast cell migration by inhibiting urokinase type plasminogen activator expression through p38 mitogen-activated protein kinase

“…Considering that uPA can also activate hepatocyte growth factor, which plays a role in promoting satellite cell migration to the site of injury (Sisson et al, 2009), we cannot exclude the possibility that IL-17 -inhibited uPA expression has, as a consequence, diminished uPA-dependent activation of growth factors, which subsequently suppressed the C2C12 migration and myogenic differentiation. Furthermore, IL-17 increases the expression of cyclooxygenase-2 (COX-2) (Kocić et al, 2012a), which by elevating prostacyclines (PGL2) production may be also implicated in the inhibition of myoblast migration as reported by Bondesen et al (2007).…”

Highly Dynamic Transcriptional Signature of Distinct Macrophage Subsets during Sterile Inflammation, Resolution, and Tissue Repair

“…The expression pattern of a series of molecules secreted by macrophages and involved in myogenesis (insulin-like growth factors, urokinase plasminogen activator, platelet-derived growth factor a, hepatocyte growth factor, bone morphogenetic protein 2 [24][25][26][27][28][29]) was increased with time of regeneration, and particularly in Ly6C neg macrophages (Fig. 3C).…”