Potential of Telomerase in Age-Related Macular Degeneration-Involvement of Senescence, DNA Damage Response and Autophagy and a Key Role of PGC-1α

Age-related macular degeneration (AMD), the main cause of vision loss in the elderly, is associated with oxidation in the retina cells promoting telomere attrition. Activation of telomerase was reported to improve macular functions in AMD patients. The catalytic subunit of human telomerase (hTERT) may directly interact with proteins important for senescence, DNA damage response, and autophagy, which are impaired in AMD. hTERT interaction with mTORC1 (mTOR (mechanistic target of rapamycin) complex 1) and PINK1 (PTEN-induced kinase 1) activates macroautophagy and mitophagy, respectively, and removes cellular debris accumulated over AMD progression. Ectopic expression of telomerase in retinal pigment epithelium (RPE) cells lengthened telomeres, reduced senescence, and extended their lifespan. These effects provide evidence for the potential of telomerase in AMD therapy. Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) may be involved in AMD pathogenesis through decreasing oxidative stress and senescence, regulation of vascular endothelial growth factor (VEGF), and improving autophagy. PGC-1α and TERT form an inhibitory positive feedback loop. In conclusion, telomerase activation and its ectopic expression in RPE cells, as well as controlled clinical trials on the effects of telomerase activation in AMD patients, are justified and should be assisted by PGC-1α modulators to increase the therapeutic potential of telomerase in AMD.

PPARGC1A DNA methylation in subcutaneous adipose tissue in low birth weight subjects--impact of 5 days of high-fat overfeeding

OBJECTIVE

Increased DNA methylation of the metabolic regulator peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PPARGC1A) has been reported in skeletal muscle from type 2 diabetes (T2D) subjects and from low birth weight (LBW) subjects with an increased risk of T2D. High-fat overfeeding increases PPARGC1A DNA methylation in muscle in a birth weight dependent manner. However, PPARGC1A DNA methylation in subcutaneous adipose tissue (SAT) in LBW subjects has not previously been investigated. Our objective was to determine PPARGC1A DNA methylation and mRNA expression in basal and insulin-stimulated SAT from LBW and matched normal birth weight (NBW) subjects during control and high-fat overfeeding.

MATERIALS/METHODS

Nineteen young healthy men with LBW and 26 NBW controls were studied after both a 5-day high-fat overfeeding and a control diet in a randomized crossover setting. DNA methylation was assessed with bisulfite sequencing and mRNA expression with quantitative real-time PCR.

RESULTS

Following high-fat overfeeding, increased SAT PPARGC1A DNA methylation was observed in LBW subjects but not in NBW controls. Basal SAT PPARGC1A mRNA expression was unaffected by diet and similar in the two groups. However, LBW subjects showed an increased SAT PPARGC1A mRNA expression during insulin-stimulation. SAT PPARGC1A methylation correlated inversely with mRNA expression during insulin-stimulation.

CONCLUSIONS

The study adds to the increasing awareness of PPARGC1A DNA methylation being flexible and influenced by high-fat overfeeding in a birth weight dependent manner with muscle and fat responding differently. Further data are needed to understand the role of PPARGC1A DNA methylation in insulin resistance and developmental programming of T2D.