Increase in mitochondrial DNA mutations impairs retinal function and renders the retina vulnerable to injury

Mouse models that accumulate high levels of mitochondrial DNA (mtDNA) mutations owing to impairments in mitochondrial polymerase γ (PolG) proofreading function have been shown to develop phenotypes consistent with accelerated aging. As increase in mtDNA mutations and aging are risk factors for neurodegenerative diseases, we sought to determine whether increase in mtDNA mutations renders neurons more vulnerable to injury. We therefore examined the in vivo functional activity of retinal neurons and their ability to cope with stress in transgenic mice harboring a neural-targeted mutant PolG gene with an impaired proofreading capability (Kasahara, et al. (2006) Mol Psychiatry11(6):577-93, 523). We confirmed that the retina of these transgenic mice have increased mtDNA deletions and point mutations and decreased expression of mitochondrial oxidative phosphorylation enzymes. Associated with these changes, the PolG transgenic mice demonstrated accelerated age-related loss in retinal function as measured by dark-adapted electroretinogram, particularly in the inner and middle retina. Furthermore, the retinal ganglion cell-dominant inner retinal function in PolG transgenic mice showed greater vulnerability to injury induced by raised intraocular pressure, an insult known to produce mechanical, metabolic, and oxidative stress in the retina. These findings indicate that an accumulation of mtDNA mutations is associated with impairment in neural function and reduced capacity of neurons to resist external stress in vivo, suggesting a potential mechanism whereby aging central nervous system can become more vulnerable to neurodegeneration.

Increasing hepatitis B viral load is associated with risk of significant liver fibrosis in HBeAg-negative but not HBeAg-positive chronic hepatitis B

BACKGROUND/AIMS

To evaluate the association between demographical features, serum ALT and HBV DNA and the prevalence of significant fibrosis and inflammation on liver biopsy in patients with chronic hepatitis B.

METHODS

In this cross-sectional study of patients on St Vincent's Hospital HBV database, patients were classified into three groups on the basis of HBeAg status and HBV DNA level and the prevalence of significant (F2/3/4) fibrosis and (A2/3) inflammation in each group was established. Patients were also divided into HBeAg-positive and -negative groups and examined for the prevalence of significant fibrosis/inflammation in the strata of HBV DNA and ALT. Predictors of significant fibrosis and inflammation in HBeAg-positive and -negative patients were examined by logistic regression.

RESULTS

Three hundred and ninety four patients (HBeAg positive=198; HBeAg negative=196) with liver biopsy were identified. Fifty-eight percent of HBeAg-negative patients with HBV DNA >25,000 IU/ml had F2/3/4 fibrosis. HBV DNA and F2/3/4 were positively correlated in HBeAg-negative patients [odds ratio (OR) 1.42, P=0.001] but inversely correlated in HBeAg-positive patients (OR 0.71, P=0.03). HBV DNA was an independent predictor of significant fibrosis in HBeAg negative (P=0.03) but not HBeAg-positive patients. In HBeAg-positive patients, age was the only predictor of significant fibrosis (P=0.001) and ALT the only predictor of significant inflammation (P=0.003). In the whole cohort there was a close positive association between inflammation and fibrosis.

CONCLUSION

Increasing levels of HBV DNA are associated with increasing prevalence of significant fibrosis only in patients with HBeAg-negative CHB.