Fibroblast Subpopulations in Radiation-induced Capsular Contracture Print

The ASERF Scientific Research Committee and Board of Directors are pleased to announce the following grant award:

Researcher: Michael Longaker, MD

Grant Award: ASERF Interim Grant

Amount Awarded: $39,000

Project Name: Fibroblast Subpopulations in Radiation-induced Capsular Contracture

Project Summary: "Breast implants, whether for augmentation or reconstruction, are associated with several well-known risks and complications, the most common of which is capsular contracture. Despite continued improvements in breast implant design over the past five decades, capsular contracture still remains a significant problem, with reported rates between 15% and 45% (Headon, Kasem et al. 2015). Furthermore, the incidence of contracture, as well as severity of contracture, is worsened by adjuvant radiation therapy for breast cancer (McCarthy, Pusic et al. 2005). Although thought to be also influenced by a variety of other exogenous factors including surgical technique, implant location, hematoma formation, and infection or biofilm formation, a common underlying etiology and pathogenesis remains poorly defined.

Capsular contracture begins as an inflammatory foreign body response after implantation, and while the ensuing fibrotic reaction can help to maintain position of the implant, an excessive response can result in pain and deformity of the breast. Histologic studies have shown an accumulation of macrophages, lymphocytes, and fibroblasts, the latter of which lay down multi-directional collagen fibers during initial capsule formation. Continued accumulation and activity of fibroblasts along with differentiation into myofibroblasts, however, results in thickened, dense bands of highly aligned fibers. Several studies have also correlated fibroblast density and cellular alignment with capsular contracture, and more recent reports have shown a functional difference in fibroblasts, with dysregulation of several inflammatory and fibrotic genes noted when comparing fibroblasts derived from non-contracted and contracted breast implant capsules (Kyle and Bayat 2015). Emerging data has now shown specific fibroblast subpopulations to exist, and in particular, CD26+ fibroblasts have been implicated in disordered dermal collagen deposition following radiotherapy (Rinkevich, Walmsley et al. 2015).

CD26, also known as dipeptidyl peptidase IV (DPP-4), is a homodimeric type II transmembrane glycoprotein closely related to fibroblast activation protein-? and functions as a serine exopeptidase for peptide hormones and for extracellular matrix remodeling (Thielitz, Vetter et al. 2008). CD26 also serves as a binding protein for fibronectin and collagen. Inhibitors of CD26 have potent anti-inflammatory effects, and their use to enhance incretin activity has already been approved by the FDA for treatment of type II diabetes (Drucker 2003). CD26 inhibitors have also been found to decrease proliferation, TGF-?1 expression, and collagen and fibronectin production by normal and keloid-derived fibroblasts (Thielitz, Vetter et al. 2008). As development of thicker and more aligned collagen fibers have been found to be a key feature of capsular contracture, CD26 inhibitors have the potential to alter severity of this fibrotic response.

Among women undergoing bilateral mastectomies with expander placement prior to adjuvant radiation therapy, studies have demonstrated an over four-fold increase in capsular contracture on the irradiated side (Chen, Momeni et al. 2016). These patients therefore offer the ability to investigate the role CD26+ fibroblasts play in the development of radiation-induced capsular contracture, with the contralateral non-irradiated, less contracted breast providing a point of comparison. Our central hypothesis is that the frequency of CD26+ fibroblasts is increased in irradiated, contracted breast capsules, and their enhanced fibrotic capacity can be reduced by CD26 inhibitors to decrease capsular contracture severity. Three Specific Aims have been proposed to evaluate this.

Specific Aim #1: To define the frequency of CD26+ fibroblasts in irradiated and non-irradiated breast implant capsules. In our preliminary data, we have observed increased numbers of CD26-staining fibroblasts within irradiated, contracted capsules relative to contralateral non-irradiated capsules. In this Aim, we will expand on this finding, using live fibroblast harvest and flow cytometry in addition to immunofluorescent staining for CD26, vimentin, and ?-smooth muscle actin (SMA) to quantify this difference.

Specific Aim #2: To determine differences in gene expression among CD26+ and CD26- fibroblasts from irradiated and non-irradiated breast capsules. Given the role of CD26+ fibroblasts in radiation-induced dermal fibrosis, we will evaluate expression of genes known to regulate inflammation (TNF-?), tissue remodeling (MMP-12), extracellular matrix deposition (TGF-?1 and COL1A1), and contracture (?-SMA) in capsule-derived fibroblasts. Live fibroblast harvest and flow cytometry will be performed to isolate CD26+, CD26-, and unsorted fibroblasts from both radiated and non-radiated capsules for transcript analysis.

Specific Aim #3: To evaluate the effects of CD26 inhibition on fibroblast function. CD26 inhibitors have been shown to reduce the fibrotic function of dermal fibroblasts. In this Aim, we will evaluate procollagen I and fibronectin production by CD26+, CD26-, and unsorted fibroblasts from radiated and non-radiated capsules in response to treatment with a CD26 inhibitor."