Sex Differences In Quadriceps Angiogenic Signaling And Muscle Capillary Supply After ACL Injury

Abstract

Following an Anterior Cruciate Ligament (ACL) reconstruction, females have worse functional outcomes; however, skeletal muscle biology has preferentially been studied in males. Muscle adaptation and recovery from injury are intimately tied to the muscle capillary network, which delivers oxygen, nutrients, and hormones to muscle fibers. PURPOSE: To examine differences in skeletal muscle angiogenic signaling and capillary supply in males and females after ACL injury. METHODS: Vastus lateralis (VL) biopsies were collected (24.6 ± 5.5 yr; 8M, 5F) from the ACL injured (INJ) and non-injured (NI) leg before reconstruction. Samples were assessed for vascular endothelial growth factor receptor 1 and 2 (VEGFR1 and VEGFR2) by western blot. Capillary to fiber ratio (C:F), capillary to fiber perimeter exchange index (CFPE), and capillary tortuosity (% fiber border directly contacting capillary wall) were assessed by immunohistochemistry. RESULTS: The percentage of phosphorylated relative to total VEGFR2 was not different between INJ and NI, but was lower in females (76.9 ± 4.1%) compared to males (89.2 ± 3.2%; P = 0.043). VEGFR2 abundance tended to be higher (P = 0.098) and C:F was lower (INJ: 2.3 ± 0.2 capillary•fiber-1, NI: 2.6 ± 0.2 capillary•fiber-1; P = 0.018) in INJ compared to NI, but neither parameter was different between sexes. VEGFR1 abundance displayed a sex by injury interaction (P = 0.004), with females having greater abundance of VEGFR1 in INJ (548 ± 54 A.U.) compared to NI (478 ± 53 A.U.; P = 0.050), while males showed the opposite (NI: 461 ± 42 A.U., INJ: 383 ± 42 A.U.). CFPE was lower in INJ compared to NI (INJ: 5.1 ± 0.3 capillary•1000μm-1, NI: 5.8 ± 0.3 capillary•1000μm-1; P = 0.002), and post-hoc analysis revealed that the difference was driven by females. Capillary tortuosity was lower in INJ (13 ± 2%) compared to NI (17 ± 2%) for females only (P = 0.006). CONCLUSION: Differences in angiogenic signaling between males and females in both INJ and NI limbs were evident, and ACL injury resulted in an exacerbated deficit in muscle capillary supply for females. These results support the idea that sex-specific differences in VL capillary network remodeling following ACL injury contribute to different functional outcomes following reconstruction and rehabilitation. Supported by NIH grants: R01 AR072061 and K23 AR062069.