Master of Science
O'Gorman, David B.
Burton, Jeremy P.
Lawson Health Research Institute
Periprosthetic joint infection (PJI) is a devastating and costly post-surgical complication that is not well understood due to the scarcity of physiologically representative experimental models. This thesis outlines the development of two 3D bioartificial human tissue models designed to study the cellular and biochemical interactions between primary fibroblasts from the shoulder capsule (SC) and infectious microorganisms. Using the Fibroblast-Bacteria Co-culture in 3D Collagen model, we demonstrated a global gene repression of metabolic and homeostatic processes in SC fibroblasts following 48 hours of co-culture with Cutibacterium acnes – the most common microbial cause of PJI in the shoulder. These cellular changes coincided with an increase in pro-inflammatory signaling. The Shoulder-Joint Implant Mimetic (S-JIM) model generated a range of oxygen levels (< 0.3% to 21% O2) that accurately represents the different microenvironments present across connective tissue layers in a shoulder joint. Electron microscopy images confirmed that the hypoxic conditions generated in the core of the S-JIM supported the anaerobic proliferation of C. acnes, but this microbial expansion resulted in the death of adjacent SC fibroblasts after 96 hours of co-culture. Using the S-JIM, we demonstrated the bactericidal effectiveness of direct vancomycin prophylaxis against C. acnes and confirmed the possibility of differentiating between healthy host tissues and C. acnes-infected tissues using mass spectrometry.
Summary for Lay Audience
Implant-associated joint infection is a devastating and costly post-surgical complication that may develop as a result of contamination during open-joint surgery. The shoulder joint is particularly susceptible to infection by Cutibacterium acnes – a species of skin bacteria that preferentially grows in the low-oxygen environments formed around the implant. The process in which C. acnes damages human connective tissues is not well understood due to the current lack of reliable models for studying joint infection. In this thesis, we outline the development of two novel 3D human tissue models of joint infection, designed to accurately replicate the cellular interactions between shoulder fibroblasts (cells that form connective tissue) and infectious microorganisms such as C. acnes in an artificial joint environment.
Our first model, the Fibroblast-Bacteria Co-culture in 3D Collagen, was used to assess the gene expression changes in shoulder fibroblasts following a period of incubation with C. acnes. We observed an overall decrease in the expression of genes involved in cell stability and growth, but an increase in the expression of genes that signal for inflammation between 24 and 48 hours. These cellular responses are consistent with joint infection.
Our second model, the Shoulder-Joint Implant Mimetic (S-JIM) was developed as a multi-layered cell culture system to replicate the range of different oxygen levels present across the layers of connective tissue in a human joint. We observed a range of oxygen levels from 21% to 0.3% O2. Imaging analysis confirmed that the low-oxygen conditions generated in the core of the S-JIM supported the proliferation of C. acnes, but this continued microbial expansion resulted in the death of adjacent shoulder fibroblasts after 96 hours. Using the S-JIM, we also demonstrated that the preemptive application of vancomycin powder (a first-choice antibiotic for clearing orthopedic infections) was successful at completely eradicating C. acnes cells from the model and prevented the development of infection. Finally, we provided proof-of-concept for the use of mass spectrometry – a method of detecting specific molecular markers – to differentiate between healthy human tissues and tissues infected with C. acnes.
Huang, Tony B., "Development of 3D Bioartificial Human Tissue Models of Periprosthetic Shoulder Joint Infection" (2021). Electronic Thesis and Dissertation Repository. 8172.
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