Fig. 3

Damaged muscle is in a hypoxic state. a Representative micrograph of a longitudinal section of a damaged TA muscle (3.5 days post-CTX) from a TIE2lacZ mouse. A low magnification of the upper area of the muscle section shows an area where the architecture is typical of a healthy muscle and where muscle fibers and microvessels border on each other. The lower area has fewer muscle fibers as well as a significant number of nuclei resulting from an acute inflammatory cell infiltration characteristic of a damaged muscle. The lower micrographs show the organization of the two areas at a higher magnification. In the damaged area, the microvessels were fully disorganized. The results are representative of two independent experiments. b Frozen cross-sections of control (saline) and damaged (3.5 days post-CTX) TA muscles previously labeled with the hypoxic PIM probe showing hypoxia (green) and laminin (red) in the tissues. There is a hypoxic zone in the damaged muscle, unlike the control muscle. The micrographs are representative of three independent experiments. c Time course of relative mRNA expression of HIF-1α after a CTX-induced muscle injury. There is a significant increase in HIF-1α culminating 3.5 days post-CTX (13.9-fold) in the damaged muscle compared to the control muscle (saline) (mean ± SEM, n = 4; ***p < 0.001). d Western blot analysis of HIF-1α and an internal control (GAPDH) in the control (saline) and damaged (CTX) muscles. The expression of HIF-1α was 7.3-fold higher in the damaged muscle, which is in agreement with the increase in mRNA levels (mean ± SEM, n = 4; *p < 0.05)