Smad3 Deficiency Ameliorates Experimental Obliterative Bronchiolitis in a Heterotopic Tracheal Transplantation Model

Abstract

Chronic allograft rejection manifested as obliterative bronchiolitis (OB) remains the single greatest impediment to long-term survival after lung transplantation. Transforming growth factor-␤1 (TGF-␤1) has been implicated in the tissue remodeling response associated with OB. Therefore, its intracellular signal transducer, Smad3, is a prime target of investigation. Herein, we examine the role of TGF-␤1, through Smad3, in the development of OB using heterotopic tracheal transplantation in wild-type and Smad3-null mice. TGF-␤1 was detectable within infiltrating mononuclear cells early after transplantation. Throughout the last 20 years, lung transplantation has evolved into an accepted treatment option for patients with end-stage lung disease because of emphysema, pulmonary fibrosis, pulmonary hypertension, and cystic fibrosis. 1 However, chronic allograft rejection manifested as obliterative bronchiolitis (OB) remains the major obstacle to long-term survival after lung transplantation. 2 Clinically, OB is characterized by airflow limitation, defined by a 20% decline in forced expiratory volume in 1 second (FEV 1 ), and is often complicated by recurrent lower respiratory tract infections. The histological hallmark of OB is the presence of obstructing intraluminal polyps comprised of fibromyxoid granulation tissue and plaques of dense submucosal eosinophilic scar on lung biopsy. OB can complicate up to 60% of lung allografts and becomes increasingly prevalent the further removed from the transplant operation. 3 Progressive OB ultimately results in worsening hypoxemia and death.Many studies on the pathogenesis of OB have concentrated on the role of cellular allogenic immune responses during OB development. However, fibroproliferation and tissue remodeling clearly play an important role in its pathogenesis because OB is characterized by the accumulation of fibroblasts and the excessive deposition of connective tissue matrix within the lumen of the affected bronchioles. The factors that initiate and maintain fibroproliferation and tissue remodeling within the airway lumen in OB have not been fully elucidated. One candidate factor is transforming growth factor (TGF)-␤, a pleiotropic cytokine with potent profibrotic activities. 4 Extensively studied in solid organ transplantation, TGF-␤ has been found to have beneficial effects on alloimmunity. For instance, overexpression of a TGF-␤ transgene leads to marked reductions in acute rejection and prolongation of graft survival in experimental heart and

Combinatorial activation of FAK and AKT by transforming growth factor-β1 confers an anoikis-resistant phenotype to myofibroblasts

“…Although studies by our group [12] and others [36] have shown the capacity of TGF-β1 to activate FAK in certain cell types, a role for SMAD3 in mediating this effect has not been previously demonstrated. The requirement for SMAD3 in FAK activation is consistent with a role for SMAD3 in myofibroblast differentiation both in-vitro [37,38] and in-vivo [39][40][41].…”

Alcohol Ingestion by Donors Amplifies Experimental Airway Disease after Heterotopic Transplantation

“…Male Sprague Dawley (SD; Charles River Laboratories, Wilmington, MA) or Fischer 344 (F344; Harlan, Indianapolis, IN) donor rats (age, 3-5 mo) were fed the Lieber-DeCarli isocaloric liquid diet, containing either ethanol (36% total calories) or Maltin-Dextrin as substitute (control diet) for 8 weeks. HTT was performed as described previously (16). Briefly, isografts or allografts were obtained by transplanting tracheas from control or alcohol-fed donor rats subcutaneously into recipient rats.…”

“…Allograft injury, as determined by epithelial loss, cellular infiltration, and collagen deposition within the lumen of the airway, was assessed at 3, 7, 14, and 21 days after transplantation, as described previously (16). Image analyses were performed as described by Schacker and colleagues (32).…”

“…Previous studies have demonstrated that OAD pathology in allografts is TGF-b 1 -dependent (16,34,35). To determine if components of the TGF-b 1 fibrogenic pathway are increased in alcohol-mediated exacerbation of OAD, 21-day allografts from control and alcohol-fed SD donors were immunostained for TGF-b 1 .…”

“…Using heterotopic tracheal transplantation (HTT) in animals to induce obliterative airway disease (OAD) as an experimental model of OB, recent studies have demonstrated that alloimmunity represents but one early component of OAD pathophysiology (15,16). Rather, OAD development appears to be mediated via two mechanisms.…”