Tissue assembly in animals requires the formation of an
extracellular matrix (ECM) containing millimeter-long collagen
fibrils arranged in elaborate 3-dimensional architectures such as
parallel bundles (in tendons and ligaments), basket-weaves (in skin
and bone) and orthogonal lattices (in cornea). A prerequisite for
fibril assembly is the cleavage of procollagen (the precursor of
fibrillar collagen) by procollagen metalloproteinases (PMPs, that
convert procollagen to collagen). Despite five decades of work on
collagen fibrils it remains controversial how the fibrils assemble
and how their structure relates to tissue organisation and function.
My research group has developed and used electron microscope (EM)
methods to study the structure of individual collagen fibrils. We
have shown that cells synthesise short (~1 ?m long) 'early collagen
fibrils' that fuse tip-to-tip to form long fibrils and tip-to-shaft
to form branching networks, at least in skin. Therefore, the
formation of long collagen fibrils does not occur by simple protein
self-assembly but is hierarchical and under cellular control.
A Wellcome Trust 5-year funded research programme builds on these
observations and tests the hypothesis that the hierarchical assembly
of collagen fibrils begins inside the cell by the formation
of procollagen-containing protein complexes. The aims of our
research are:
- To determine the 3-dimensional structure of collagen fibrils
to understand how the structure relates to tissue organisation;
- To elucidate how cells synthesize collagen early fibrils
having a precise size and shape;
- To determine the structure-function of PMPs in the formation
of early fibrils;
- To elucidate how procollagen and the PMPs are trafficked to
the ECM.
- To determine where in tissue procollagen is converted to
collagen by the PMPs;
- To design and synthesise novel recombinant procollagens having
new biological properties, for use in tissue engineering
applications.
Four convergent strategies are being used to achieve these aims.
The first is to use automated electron tomography (AET) to determine
the 3-dimensional structure of individual collagen fibrils and the
cell-ECM interface. The second is to use site-directed mutagenesis
and recombinant protein expression to understand how the PMPs bind
procollagen and convert it to collagen during the formation of
collagen early fibrils. The third is to elucidate the biochemical
composition of collagen early fibrils. The fourth is to use
biochemistry, bioimaging and colloidal gold EM techniques to
understand the trafficking of macromolecular protein complexes
during tissue assembly. Information obtained from this work will be
relevant to understanding the pathway of events leading to fibrosis,
osteoarthritis and wound healing where abnormal synthesis of
collagen occurs.
A project in the laboratory, funded by Wellcome Trust Catalyst
BioMedica Ltd, is evaluating the use of novel collagens in the
formation of skin substitutes, for example, for the treatment of
burns. The aims of the project are to exemplify our existing patents
and to strengthen our intellectual property in the area of novel
collagen molecules. The specific aims of the project are to produce
recombinant procollagens with essential features targeted at:
- Cell-delivery.
- Growth factor delivery
- Influence of cell differentiation.
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