Ligamentous constraint of the first carpometacarpal joint.

To examine the role of the ligaments in maintaining stability of the first carpometacarpal (CMC) joint, a sequential ligament sectioning study of sixteen specimens was performed. While a small compressive force was maintained, loads were applied to displace each specimen in four directions - volar, dorsal, radial, and ulnar. Translations of the specimen in both dorsal-volar and radial-ulnar axes were measured. Initially, the tests were conducted with the specimen intact. These tests were then repeated following sectioning of the CMC anterior oblique ligament (AOL), ulnar collateral ligament (UCL), intermetacarpal ligament (IML) and dorsal radial ligament (DRL). The first CMC joint translation was increased in the absence of IML and DRL (p < 0.05). Both IML and DRL were important in constraining the first CMC joint translation against external applied loads. Potential applications of these findings include the treatment of joint hypermobility and the reduction or delay of onset or progression of first CMC joint osteoarthritis.

Age-associated mitochondrial DNA mutations cause metabolic remodelling that contributes to accelerated intestinal tumorigenesis.

Oxidative phosphorylation (OXPHOS) defects caused by somatic mitochondrial DNA (mtDNA) mutations increase with age in human colorectal epithelium and are prevalent in colorectal tumours, but whether they actively contribute to tumorigenesis remains unknown. Here we demonstrate that mtDNA mutations causing OXPHOS defects are enriched during the human adenoma/carcinoma sequence, suggesting they may confer a metabolic advantage. To test this we deleted the tumour suppressor Apc in OXPHOS deficient intestinal stem cells in mice. The resulting tumours were larger than in control mice due to accelerated cell proliferation and reduced apoptosis. We show that both normal crypts and tumours undergo metabolic remodelling in response to OXPHOS deficiency by upregulating the de novo serine synthesis pathway (SSP). Moreover, normal human colonic crypts upregulate the SSP in response to OXPHOS deficiency prior to tumorigenesis. Our data show that age-associated OXPHOS deficiency causes metabolic remodelling that can functionally contribute to accelerated intestinal cancer development.

Production of transmitochondrial cybrids containing naturally occurring pathogenic mtDNA variants.

The human mitochondrial genome (mtDNA) encodes polypeptides that are critical for coupling oxidative phosphorylation. Our detailed understanding of the molecular processes that mediate mitochondrial gene expression and the structure-function relationships of the OXPHOS components could be greatly improved if we were able to transfect mitochondria and manipulate mtDNA in vivo. Increasing our knowledge of this process is not merely of fundamental importance, as mutations of the mitochondrial genome are known to cause a spectrum of clinical disorders and have been implicated in more common neurodegenerative disease and the ageing process. In organellar or in vitro reconstitution studies have identified many factors central to the mechanisms of mitochondrial gene expression, but being able to investigate the molecular aetiology of a limited number of cell lines from patients harbouring mutated mtDNA has been enormously beneficial. In the absence of a mechanism for manipulating mtDNA, a much larger pool of pathogenic mtDNA mutations would increase our knowledge of mitochondrial gene expression. Colonic crypts from ageing individuals harbour mutated mtDNA. Here we show that by generating cytoplasts from colonocytes, standard fusion techniques can be used to transfer mtDNA into rapidly dividing immortalized cells and, thereby, respiratory-deficient transmitochondrial cybrids can be isolated. A simple screen identified clones that carried putative pathogenic mutations in MTRNR1, MTRNR2, MTCOI and MTND2, MTND4 and MTND6. This method can therefore be exploited to produce a library of cell lines carrying pathogenic human mtDNA for further study.

Age-associated mitochondrial DNA mutations lead to small but significant changes in cell proliferation and apoptosis in human colonic crypts.

Mitochondrial DNA (mtDNA) mutations are a cause of human disease and are proposed to have a role in human aging. Clonally expanded mtDNA point mutations have been detected in replicating tissues and have been shown to cause respiratory chain (RC) defects. The effect of these mutations on other cellular functions has not been established. Here, we investigate the consequences of RC deficiency on human colonic epithelial stem cells and their progeny in elderly individuals. We show for the first time in aging human tissue that RC deficiency attenuates cell proliferation and increases apoptosis in the progeny of RC deficient stem cells, leading to decreased crypt cell population.