Investigating the Molecular basis of Cole Carpenter Syndrome

Cole Carpenter syndrome (CCS) is a rare genetic syndrome affecting bone integrity and durability. It is believed to be related to osteogenesis imperfecta (OI), a group of genetic disorders commonly known as brittle bone disease. The molecular mechanism of the syndrome has yet to be discovered, however two distinct types have been identified: CCS1 and CCS2, linked to mutations in protein disulphide isomerase (PDI), and SEC24D (a component of the COPII vesicle export complex) respectively. This thesis will provide groundwork in investigating the molecular basis of CCS1. This variant is characterised by a single amino acid substitution mutation (Y393C) in PDI, an endoplasmic reticulum (ER) specific protein disulphide isomerase and molecular chaperone involved in collagen folding. Without this chaperone, collagen cannot fold into its triple helical tertiary structure, and this misfolded protein may accumulate in the ER, activating the unfolded protein response (UPR). It has been suggested that a failure to resolve this response may result in the brittle bone phenotype of Cole Carpenter syndrome. This thesis presents work in both primary cells and established cell lines to identify potential interacting partners of Y393C-PDI, hypothesising the potential downstream effects on collagen matrix production. Indirect immunofluorescent labelling of collagen I suggests that collagen production is impaired, and confocal microscopy revealed abnormal ER and lysosome organelle morphologies in Y393C-PDI expressing cells. Overall cell viability of affected cells appears significantly decreased, and they are less influenced by the action of small molecule inhibitors than wild-type cells. Altogether, these preliminary data shed light on the cause of the bone specific phenotype of Cole Carpenter Syndrome 1, and potentially help to understand other OI-related disorders.