Biology subjects

Holmes, D. F.

Publications and source records attributed to Holmes, D. F..

5 recordsLinked to original sources

bioRxiv2022

Fibrillin microfibril structure identifies long-range effects of inherited pathogenic mutations affecting a key regulatory TGFβ-binding site

Genetic mutations in fibrillin microfibrils cause a range of serious inherited diseases such as Marfan syndrome (MFS) and Weill-Marchesani syndrome (WMS). These diseases typically show major dysregulation of tissue development and growth, particularly in skeletal long bones, but links between the mutations and the diseases are unknown. In this study we reveal the detailed cryo-EM structure of native fibrillin microfibrils from mammalian tissue. The major bead region showed pseudo 8-fold symmetry and a buried protease resistant N-terminal core. Based on this structure, we show a WMS deletion mutant induces a rearrangement with long-range effects blocking interaction with latent TGF{beta}-binding protein (LTBP)-1 at a remote site. Separate deletion of this binding site resulted in the assembly of shorter fibrillin microfibrils with structural alterations. These results establish that in complex extracellular protein assemblies, such as in fibrillin, mutations may have long-range structural consequences to disrupt growth factor signalling and cause disease.

biochemistry↗

bioRxiv2020

Analysis of opticin binding to collagen fibrils identifies a single binding site in the gap region and a high specificity towards thin heterotypic fibrils containing collagens II, and XI or V/XI.

Opticin is a class III member of the extracellular matrix small leucine-rich repeat protein/proteoglycan (SLRP) family found in vitreous humour and cartilage. It was first identified associated with the surface of vitreous collagen fibrils and several other SLRPs are also known to bind collagen fibrils and it some cases alter fibril morphology. The purpose of this study was to investigate the binding of opticin to the collagen II-containing fibrils found in vitreous and cartilage. Electron microscopic studies using gold labelling demonstrated that opticin binds vitreous and thin cartilage collagen fibrils specifically at a single site in the gap region of the collagen D-period corresponding to the e2 stain band; this is the first demonstration of the binding site of a class III SLRP on collagen fibrils. Opticin did not bind thick cartilage collagen fibrils from cartilage or tactoids formed in vitro from collagen II, but shows high specificity for thin, heterotypic collagen fibrils containing collagens II, and XI or V/XI. Vitreous collagen fibrils from opticin null and wild-type mice were compared and no difference in fibril morphology or diameter was observed. Similarly, in vitro fibrillogenesis experiments showed that opticin did not affect fibril formation. We propose that when opticin is bound to collagen fibrils, rather than influencing their morphology it instead hinders the binding of other molecules to the fibril surfaces and/or act as an intermediary bridge linking the collagen fibrils to other non-collagenous molecules.

biochemistry↗

bioRxiv2019

Estrogen mediates acute elastic fibre homeostasis in skin

Remodelling of the dermal extracellular matrix makes a major contribution to skin fragility in the elderly. The peri-menopausal period in females is also associated with an age-like phenotype which can be reversed by hormone replacement therapy. This suggests a direct link between circulating hormone levels and tissue ageing. Despite work investigating the role of estrogen as a regulator of collagen fibril abundance and structure, the influence of estrogen on the elastic fibre system remains poorly defined. Here we used an ovariectomised (Ovx) mouse surgical menopause model to show that just 7 weeks of acute hormone deficiency significantly decreased skin tensile strength and elasticity. Systemic replacement of 17{beta}-estradiol to physiological levels protected against these changes to the skin mechanical properties. Moreover, acute hormone deficiency differentially influenced dermal structural networks, significantly decreasing dermal elastic fibre abundance without discernible effect on collagen fibril organisation or abundance. We suggest that this specific elastic fibre proteolysis may be driven by extracellular protease activity, or be a consequence of significant adipocyte hypertrophy. 17{beta}-estradiol supplementation in Ovx mice in vivo protected the elastic fibre system. Treatment of human dermal fibroblasts with 17{beta}-estradiol in vitro induced the selective upregulation of tropoelastin, fibrillin-1 and associated elastic fibre-associated proteins (including EMILINs and fibulins). In summary, these data show that the elastic fibre system is significantly perturbed by estrogen deprivation. Thus, pharmacological intervention may slow the acute effects of menopause and potentially the chronic effects of ageing in skin.

biophysics↗

bioRxiv2019

Distinct matrix composition and mechanics in aged and estrogen-deficient mouse skin

Hormone deficiency has been widely linked to accelerated tissue ageing, and increased incidence of chronic degenerative disease. Furthermore, age-associated hormonal dysregulation is thought to be a major contributing factor to the increased fragility of aged skin. The ageing process is driven by an aggregation of damage to cells and extracellular matrix, which can directly influence the mechanical properties of the tissue. Here we report on the correlation between mechanical properties and composition of skin from ovariectomised and aged mice, to assess the extent to which estrogen deprivation drives dermal ageing. We found that age and estrogen abrogation affected skin mechanical properties in contrasting ways: ageing led to increased tensile strength and stiffness while estrogen deprivation had the opposite effect. Mass spectrometry proteomics showed that the quantity of extractable fibrillar collagen-I decreased with ageing, but no change was observed in ovariectomised mice. This observation, in combination with measurements of tensile strength, was interpreted to reflect changes to the extent of extracellular matrix crosslinking, supported by a significant increase in the staining of advanced glycation endpoints in aged skin. Loss of mechanical strength in the skin following ovariectomy was consistent with a loss of elastic fibres. Other changes in extracellular matrix composition broadly correlated between aged and ovariectomised mice, confirming the important role of estrogen-related pathways in ageing. This study offers new insight into the relationship between tissue composition and mechanics, and suggests that the deleterious effects of intrinsic skin ageing are compounded by factors beyond hormonal dysregulation.

biophysics↗

bioRxiv2018

Circadian Clock Regulation of the Secretory Pathway

Collagen is the most abundant secreted protein in vertebrates that persists throughout life without renewal. The unchanging nature of collagen contrasts with observed continued collagen synthesis throughout adulthood and with conventional transcriptional and translational homeostatic mechanisms that replace damaged proteins with new copies. Here we show circadian clock regulation of procollagen transport from ER-to-Golgi and Golgi-to-plasma membrane by sequential rhythmic expression of SEC61, TANGO1, PDE4D and VPS33B. The result is nocturnal procollagen synthesis and daytime collagen fibril assembly in mice. Rhythmic collagen degradation by CTSK maintains collagen homeostasis. This circadian cycle of collagen synthesis, assembly and degradation affects only a pool of newly-synthesized collagen whilst maintaining the persistent collagen network. Disabling the circadian clock causes collagen accumulation and abnormal fibrils in vivo. In conclusion, our study has identified a circadian clock mechanism of protein homeostasis in which a sacrificial pool of collagen is synthesized and removed to maintain tissue function.

cell biology↗