Abstract
Caesarean section (C/S) is a common surgical procedure performed as an alternative to vaginal birth to deliver babies. The rate of C/S has grown rapidly and is predicted to reach one in three childbirths by 2030. With the increasing incidence of C/S, an increase in the complications linked to this surgery can be expected. Complications that occur in up to 15% of C/S wounds include seromas, infections, wound dehiscence, abdominal adhesions and excessive scarring. These complications can impede wound closure, the mother’s recovery, and subsequent C/S or abdominal surgeries. Women suffering from obesity have a greater risk of C/S wound healing complications, while women with a C/S history have greater experience risk of abdominal adhesions, excessive scarring, and delays in subsequent C/S deliveries.
Successful wound healing is dependent on phasic interactions between tissue-resident and infiltrating cells, secreted regulatory factors, and a network of macromolecules called the extracellular matrix (ECM). The ECM, which is composed of collagens, proteoglycans, and glycoproteins, is tightly linked to the inflammatory, proliferative, and remodelling phases of healing, as well as consequences of dysfunctional healing, namely adhesions and hypertrophic or keloid scars. Importantly, the ECM at the primary site of wound healing complications, the abdominal subcutaneous adipose tissue (SAT), has not been investigated in the context of C/S wound healing, but differs in its architecture and composition with obesity.
Management strategies for C/S wounds include surgical refinements, wound drainage and debridement, and the application of wet or dry dressings. However, none of these approaches target the SAT or actively promote healing. Adipose tissue engineering (ATE) has recently been applied to treat chronic wounds, combining biomaterials inspired from natural ECM components with and without adipose-derived cells to facilitate healing of the SAT. This approach may also be beneficial for C/S wounds, but little is known about the molecular processes that lead to their dysfunctional healing. Given that the ECM greatly influences healing outcomes, it was hypothesised that the SAT ECM composition will change within obese and repeated C/S women that are more at risks of developing to C/S wound healing complications. . This research, therefore, aimed to identify ECM components associated with successful and dysfunctional SAT healing. The intent being to identify an appropriate choice of biomaterial for use in ATE approaches aimed at preventing the development of C/S wound complications.
Firstly, a systemic literature review was conducted of studies investigating the composition, architecture, and function of the ECM in human white adipose tissue (WAT). The aim was to identify appropriate scientific strategies and methodologies to investigate the SAT ECM from human C/S wounds. Observational studies which explored the ECM composition and architecture were more common than experimental studies investigating ECM function. These studies predominantly investigated WAT ECM changes associated with obesity, while little research investigated the WAT ECM in a wound healing context. Further, there were no investigations into how surgical wounds influence the SAT ECM, nor how the SAT ECM impacts the healing process after repeated wounding or in the context of obesity. Multiple genetic, histological and protein analyses were generally applied to study compositional changes in SAT ECM, while functional analyses using SAT-derived cells utilised both two- and three-dimensional culture. This review confirmed the need to investigate the SAT ECM and its potential role in healing complications following C/S and provided guidance as to the experimental design needed to address the hypothesis of this thesis.
The ECM of SAT samples from human C/S wounds was next characterised relative to the clinical factors associated with impaired healing and scarring. The SAT samples were obtained from otherwise healthy donors grouped according to their body mass index (non-obese versus obese) and C/S history (no or prior). Despite no significant differences in total collagen content or organisation being observed between the study populations, there was a trend towards increased sulfated glycosaminoglycan (GAG) content relative to C/S history. Proteomic studies using mass spectrometry revealed that specific collagens, glycoproteins, proteoglycans, and ECM-associated proteins were differentially abundant in participants relative to C/S history and obesity. This included a trend towards an increase in fibronectin and decorin in the SAT ECM of participants with C/S history relative to those without. Thus, changes do occur in the ECM at the site of C/S wounds in individuals presenting with prior C/S history, and to a lesser extent obesity, who are most likely to suffer from healing and scarring complications.
The impact of ECM components on the healing responses of adipose-derived cells was then examined in two-dimensional (2D) and three-dimensional (3D) culture. Stromal vascular fraction (SVF) cells were obtained from the SAT biopsies from otherwise healthy donors, while the ECM components selected were commonly used ATE biomaterials that varied or not with obesity or C/S history. In 2D culture, the sulphated GAG heparan sulfate (HS) increased SVF cell migration and proliferation, while fibronectin increased SVF cell attachment and migration, while inhibiting fibrogenesis. However, collagen type I and gelatin did not influence SVF cell function to the same extent. In 3D, light-activated, cross-linked, gelatin hydrogels, the addition of HS or fibronectin did not impact SVF cell lipid accumulation when cultured in adipogenic conditions, but influenced the size and pericellular ECM deposition of the maturing adipocytes. Further, fibronectin altered SVF cell morphology and reduced their contractility when cultured in fibrotic conditions. Thus, SAT ECM components, that change relative to clinical factors associated with C/S wound complications, do impact the healing capabilities of C/S wound SAT-derived cells in vitro.
In summary, this is the first report of ECM compositional changes in SAT from C/S wounds associated with prior C/S history and obesity. Further, this study revealed that ECM components which change relative to these clinical factors impact the healing capabilities of SAT-derived cells. Thus, this research provides a greater understanding of how the SAT ECM may influence healing outcomes following C/S. Further, it provided evidence that specific ECM components may act as pro-healing or anti-fibrotic biomaterials if used in ATE approaches to prevent healing complications following Caesarean delivery.