Fibroblasts are the most common cell type in connective tissue. They can be compared to 'nature's stitches', holding together damaged tissue until it is healed. Fibroblasts remain sleeping until they are needed for tissue repair, releasing components that form the extracellular matrix (ECM) and help rebuild tissue. Wound healing being a very complex and delicate process, Mirko D'Urso explored how subtle changes in the environment influence fibroblast behaviour.
Fibroblasts are not only very common in the human body, but they are also extremely versatile. Some fibroblasts can transform into different cells, and they are able to produce a wide range of proteins and products that facilitate wound healing and regulate various cellular processes.
The delicate process of wound healing
Wound healing is a complex process that aims to restore the structural and functional integrity of damaged tissues. Fibroblasts are central to connective tissue architecture and are crucial in the journey from injury to tissue repair.
When tissue is damaged and needs repair, fibroblasts are among the first responders, navigating through various phases of tissue healing, and transforming into microfibroblasts along the way, through a process called fibroblast-to-myofibroblast phenotype transition (FMT).
Fibroblasts to the rescue
Fibroblasts are versatile as a type of cells since they can respond to certain biochemical and biophysical signals. Moreover, they are involved in the tissue healing process at different levels of complexity.
However, a lot is unknown still about exactly how the different microenvironmental signals (chemical, mechanical, and physical) influence fibroblasts during wound healing. We need a better understanding of these processes to prevent problems during wound healing, such as infections, haemorrhaging and necrosis, which can lead to the formation of chronic pathological state of tissues such as fibrosis and scar formation.
When tissue is damaged and the body has a wound, inflammation flares up. Fibroblasts wake up and migrate to the wound site within 48 hours after the inflammatory response cascade takes place, guided by chemical signals that stimulate movement towards the wound site.
There, fibroblasts get to work, clearing debris and changing the local environment to enable subsequent healing stages. They start to multiply, synthesize products and proteins such as collagen, elastin, and fibronectin. These are all elements of the extracellular matrix. The extracellular matrix (ECM) is a large network of proteins and other molecules that surround, support and give structure to cells and tissues in the body. Restoring the extracellular matrix is of crucial importance during wound healing.
Shapeshifting cells
During wound healing, the tissue around the damaged area changes in stiffness and other mechanical and physical properties. Fibroblasts respond to these changes by 'waking up' (inflammatory state), after which they transform into a new cell type, the myofibroblast phenotype (matrix-producing state), and start contracting the surrounding tissue.
The metamorphosis which fibroblasts undergo changing into myofibroblasts is named fibroblast-to-myofibroblasts transition (FMT). It is unclear how the multitude of microenvironmental inputs (mechanical, physical, and biochemical cues) influences this phenotypical change.
Mirko D'Urso's research delves into the shapeshifting role of fibroblasts in wound healing. He defended his PhD thesis at the Department of Biomedical Engineering on Januari 21. D'Urso is specifically interested in the impact of the microenvironment on fibroblasts during tissue repair. He developed innovative tools and methods to examine how mechanical and physical cues regulate fibroblast behaviour, from individual cell-level sensing to more complex scenarios involving inflammation-induced activation.
Studying fibroblasts in artificial, hydrogel landscapes
When a wound occurs, fibroblasts move along a temporary "guide" made of a protein called fibronectin to reach the wound site. To mimic and study this process, D'Urso printed proteins on a flat surface (2-D protein micropatterns). These patterns act like a guide for the fibroblasts, like the fibronectin guides in real wounds.
He further showed that fibroblasts respond to their physical environment by changing their structure and properties. These changes are largely controlled by focal adhesions, which act as sensors and attachment points for the cells.
During these explorations the team accidentally discovered a fibroblasts in the so-called "matrifibrocyte state" in the skin. Normally this type of fibroblasts is only found in the heart, therefore this research helped expanding our understanding of wound healing processes and fibroblast's tissue-specific roles.
To better study fibroblast behaviour in controlled environments, hydrogels were created to act as artificial "landscapes" that mimic cellular environments. The hydrogel landscapes are highly programmable: the features can be designed using any digital drawing software, while the dimensions and resolution can be easily tuned via UV exposure dose or photoinitiator concentration.
Better understanding tissue diseases
D'Urso also analysed how changing the hydrogel landscape influences the process of metamorphosis from fibroblast to myofibroblast. During wound healing, fibroblast transformation is typically necessary for proper tissue repair. But a persistently activated myofibroblast state causes tissue diseases, such as asthma and fibrosis. A better understanding of the transformation process might help to control the progression of these diseases.
The interaction between immune cells, particularly macrophages, and fibroblasts plays a crucial role in tissue repair and regeneration, especially during the early inflammatory phase. When a wound starts healing, macrophages are among the first responders, releasing a communication signal called cytokine, which calls fibroblasts to the wound site.
The presence of cytokines and growth factors (such as TGF-β) in the microenvironment can stimulate fibroblast responses and help regulate the healing process.
In conclusion, this work highlights the significant role of microenvironmental mechanical and physical cues in tissue regulation, crucial in biological processes such as wound healing. The study characterises fibroblasts' involvement in tissue repair, focusing on the transition from fibroblast to myofibroblast phenotype, regulated by mechanosensing and stiffness changes.
Title of PhD thesis: Mechanobiological characterization of fibroblast phenotype at different organizational and temporal scales . Supervisors: Dr. Nicholas Kurniawan Prof. Dr. Carlijn Bouten.
