Effects of Binge Alcohol Exposure on Canonical Wnt Signaling During Fracture Repair
Excessive alcohol consumption is associated with increased fracture risk, delayed bone healing and fracture non-union. Binge alcohol consumption has occurred in 25-40% of all orthopaedic trauma cases. The canonical Wnt pathway, through tight regulation of stabilized beta-catenin, plays an essential and pivotal role in the formation of new bone and cartilage to initiate bone repair. We sought to determine the molecular mechanisms behind alcohol-related fracture complications by testing the hypothesis that binge alcohol exposure deregulates canonical Wnt signaling in the fracture callus, leading to impaired healing. To test this, C57BL/6 or beta-catenin/TCF-reporter male mice were exposed to intraperitoneal alcohol or saline for 3 consecutive days for either 1 week or 2 week cycles. One hour after the final injection, mice received a stabilized tibial fracture and were sacrificed 1,2,3, 6, 9, or 14 days post-injury. Alcohol significantly decreased biomechanical strength, size, and volume of day 14 fracture calluses. Histological analysis revealed that alcohol exposure inhibited chondrocyte hypertrophy and endochondral ossification. Western blot demonstrated that the temporal expression of stabilized beta-catenin in callus tissue was significantly disrupted by alcohol at days 1, 3, 6, 9, and 14 post fracture compared to controls. The disruption in beta-catenin protein levels corresponded to spatial and quantitative modulations in Wnt-specific transcriptional activity in fracture callus sections from alcohol-treated TCF-reporter mice. Alcohol significantly decreased the mRNA levels of Wnt target genes involved in bone repair including Sox9, Runx2, beta-catenin, GSK-3beta, and Axin. Lastly, alcohol-treated mice that received LiCl showed improved callus strength, restoration of normal cartilage formation and endochondral ossification in the callus tissue, and enhanced total and activated beta-catenin protein levels to those seen in saline-treated mice. LiCl exerted these effects by reducing levels of activated GSK-3beta in the alcohol-treated group to control levels. This study shows that alcohol causes significant deregulation of Wnt/beta-catenin signaling, which may play a critical role in long-term fracture healing complications seen clinically in alcoholics. Therapies that aim to exogenously activate the Wnt pathway during healing may improve fracture repair in alcohol-abusing individuals.
Alcohol, Beta-catenin, Fracture, Wnt, Cell Biology
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