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Critical limb ischemia (CLI) is the most severe complication of peripheral arterial disease (PAD). Understanding the molecular mechanisms underlying tissue repair after CLI is necessary for preventing PAD progression. Y-box binding protein-1 (YB-1) regulates the expression of many genes in response to environmental stresses. We aimed to determine whether YB-1 is involved in ischemic muscle regeneration. A mouse ischemic hind-limb model was generated; namely, the femoral, saphenous, and popliteal arteries in the left hind limb were ligated. The right hind limb, with skin incisions alone, served as control. Hind limbs (n = 3-5 for each time point) were examined on day 0 (before the operation) and on postoperative days 1, 2, 7, 10, and 14, and the biceps femoris, adductor, rectus femoris, and gracilis muscles were subjected to histopathological and immunohistochemical analyses. In ischemic limbs, myogenesis, triggered by an increase in myotubes, began on day 7; thereafter, regenerated muscles gradually increased in volume. RT-PCR analysis showed that YB-1 mRNA levels were increased in the limbs after ischemic injury, peaked on day 2, and subsequently decreased. On day 7, expression levels of MyoD and alphasmooth muscle actin (a SMA) mRNAs were significantly higher in ischemic muscles than in control muscles. Immunohistochemical analysis revealed increased YB-1 immunoreactivity in myoblasts and myotubes on day 7, which was decreased by day 14. The immunoreactive aSMA and smooth muscle myosin heavy chain were transiently increased in myotubes. This is the first report showing the increased expression of YB-1 during muscle regeneration after ischemic injury. [ABSTRACT FROM AUTHOR]