Small molecule activators of SIRT1 replicate signaling pathways triggered by calorie restriction in vivo.

BACKGROUND: Calorie restriction (CR) produces a number of health benefits and ameliorates diseases of aging such as type 2 diabetes. The components of the pathways downstream of CR may provide intervention points for developing therapeutics for treating diseases of aging. The NAD+-dependent protein deacetylase SIRT1 has been implicated as one of the key downstream regulators of CR in yeast, rodents, and humans. Small molecule activators of SIRT1 have been identified that exhibit efficacy in animal models of diseases typically associated with aging including type 2 diabetes. To identify molecular processes induced in the liver of mice treated with two structurally distinct SIRT1 activators, SIRT501 (formulated resveratrol) and SRT1720, for three days, we utilized a systems biology approach and applied Causal Network Modeling (CNM) on gene expression data to elucidate downstream effects of SIRT1 activation. RESULTS: Here we demonstrate that SIRT1 activators recapitulate many of the molecular events downstream of CR in vivo, such as enhancing mitochondrial biogenesis, improving metabolic signaling pathways, and blunting pro-inflammatory pathways in mice fed a high fat, high calorie diet. CONCLUSION: CNM of gene expression data from mice treated with SRT501 or SRT1720 in combination with supporting in vitro and in vivo data demonstrates that SRT501 and SRT1720 produce a signaling profile that mirrors CR, improves glucose and insulin homeostasis, and acts via SIRT1 activation in vivo. Taken together these results are encouraging regarding the use of small molecule activators of SIRT1 for therapeutic intervention into type 2 diabetes, a strategy which is currently being investigated in multiple clinical trials.

Essential roles for cohesin in kinetochore and spindle function in Xenopus egg extracts.

To facilitate their accurate distribution by the mitotic spindle, sister chromatids are tethered during DNA replication, attached by their kinetochores and bi-oriented on the spindle, and then simultaneously released at the metaphase to anaphase transition, allowing for their segregation to opposite spindle poles. The highly conserved cohesin complex is fundamental to this process, yet its role in mitosis is not fully understood. We show that depletion of cohesin from Xenopus egg extracts impairs sister chromatid cohesion and kinetochore-microtubule interactions, causing defective spindle attachments and chromosome alignment during metaphase and mis-segregation during anaphase. In the absence of cohesin, sister kinetochore pairing and centromeric localization of chromosomal passenger proteins INCENP and aurora B were lost upon bipolar spindle attachment. However, kinetochores remained paired with normal passenger localization if bipolar spindle formation was prevented by inhibiting the kinesin-5 motor (Eg5). These observations indicate that cohesin is not required to establish sister association, but is necessary to maintain cohesion in the presence of bipolar spindle forces. Co-depletion of cohesin together with another major SMC complex, condensin, revealed cumulative effects on spindle assembly and chromosome architecture. These data underscore the essential requirement for cohesin in sister chromatid cohesion, kinetochore and spindle function.