Ubiquitin-specific protease-14 reduces cellular aggregates and protects against mutant huntingtin-induced cell degeneration: involvement of the proteasome and ER stress-activated kinase IRE1α.

Huntington's disease (HD) is an autosomal inherited neurological disease caused by a CAG-repeat expansion in the first exon of huntingtin gene encoding for the huntingtin protein (Htt). In HD, there is an accumulation of intracellular aggregates of mutant Htt that negatively influence cellular functions. The aggregates contain ubiquitin, and part of the HD pathophysiology could result from an imbalance in cellular ubiquitin levels. Deubiquitinating enzymes are important for replenishing the ubiquitin pool, but less is known about their roles in brain diseases. We show here that overexpression of the ubiquitin-specific protease-14 (Usp14) reduces cellular aggregates in mutant Htt-expressing cells mainly via the ubiquitin proteasome system. We also observed that the serine-threonine kinase IRE1 involved in endoplasmic reticulum (ER) stress responses is activated in mutant Htt-expressing cells in culture as well as in the striatum of mutant Htt transgenic (BACHD) mice. Usp14 interacted with IRE1 in control cells but less in mutant Htt-expressing cells. Overexpression of Usp14 in turn was able to inhibit phosphorylation of IRE1α in mutant Htt-overexpressing cells and to protect against cell degeneration and caspase-3 activation. These results show that ER stress-mediated IRE1 activation is part of mutant Htt toxicity and that this is counteracted by Usp14 expression. Usp14 effectively reduced cellular aggregates and counteracted cell degeneration indicating an important role of this protein in mutant Htt-induced cell toxicity.

Levels of glial cell line-derived neurotrophic factor are decreased, but fibroblast growth factor 2 and cerebral dopamine neurotrophic factor are increased in the hippocampus in Parkinson's disease.

Growth factors can facilitate hippocampus-based learning and memory and are potential targets for treatment of cognitive dysfunction via their neuroprotective and neurorestorative effects. Dementia is common in Parkinson's disease (PD), but treatment options are limited. We aimed to determine if levels of growth factors are altered in the hippocampus of patients with PD, and if such alterations are associated with PD pathology. Enzyme-linked immunosorbent assays were used to quantify seven growth factors in fresh frozen hippocampus from 10 PD and nine age-matched control brains. Western blotting and immunohistochemistry were used to explore cellular and inflammatory changes that may be associated with growth factor alterations. In the PD hippocampus, protein levels of glial cell line-derived neurotrophic factor were significantly decreased, despite no evidence of neuronal loss. In contrast, protein levels of fibroblast growth factor 2 and cerebral dopamine neurotrophic factor were significantly increased in PD compared to controls. Levels of the growth factors epidermal growth factor, heparin-binding epidermal growth factor, brain-derived neurotrophic factor and mesencephalic astrocyte-derived neurotrophic factor did not differ between groups. Our data demonstrate changes in specific growth factors in the hippocampus of the PD brain, which potentially represent targets for modification to help attenuate cognitive decline in PD. These data also suggest that multiple growth factors and direction of change needs to be considered when approaching growth factors as a potential treatment for cognitive decline.

Obesity Is Associated With Low NAD(+)/SIRT Pathway Expression in Adipose Tissue of BMI-Discordant Monozygotic Twins.

CONTEXT: Sirtuins (SIRTs) regulate cellular metabolism and mitochondrial function according to the energy state of the cell reflected by NAD(+) levels. OBJECTIVE: Our aim was to determine whether expressions of SIRTs and NAD(+) biosynthesis genes are affected by acquired obesity and how possible alterations are connected with metabolic dysfunction while controlling for genetic and familial factors. DESIGN AND PARTICIPANTS: We studied a cross-sectional sample of 40 healthy pairs of monozygotic twins, including 26 pairs who were discordant for body mass index (within-pair difference > 3 kg/m(2)), from the FinnTwin12 and FinnTwin16 cohorts. MAIN OUTCOME MEASURES: Subcutaneous adipose tissue (SAT) transcriptomics was analyzed by using Affymetrix U133 Plus 2.0 chips, total SAT (poly-ADP) ribose polymerase (PARP) activity by an ELISA kit, body composition by dual-energy x-ray absorptiometry and magnetic resonance imaging/spectroscopy, and insulin sensitivity by an oral glucose tolerance test. RESULTS: SIRT1, SIRT3, SIRT5, NAMPT, NMNAT2, NMNAT3, and NRK1 expressions were significantly down-regulated and the activity of main cellular NAD(+) consumers, PARPs, trended to be higher in the SAT of heavier co-twins of body mass index-discordant pairs. Controlling for twin-shared factors, SIRT1, SIRT3, NAMPT, NMNAT3, and NRK1 were significantly negatively correlated with adiposity, SIRT1, SIRT5, NMNAT2, NMNAT3, and NRK1 were negatively correlated with inflammation, and SIRT1 and SIRT5 were positively correlated with insulin sensitivity. Expressions of genes involved in mitochondrial unfolded protein response were also significantly down-regulated in the heavier co-twins. CONCLUSIONS: Our data highlight a strong relationship of reduced NAD(+)/SIRT pathway expression with acquired obesity, inflammation, insulin resistance, and impaired mitochondrial protein homeostasis in SAT.

Weight Loss Is Associated With Increased NAD(+)/SIRT1 Expression But Reduced PARP Activity in White Adipose Tissue.

CONTEXT: Sirtuins (SIRTs) and poly(ADP-ribose) polymerases (PARPs) are 2 important nicotinamide adenine dinucleotide (NAD)(+)-dependent enzyme families with opposing metabolic effects. Energy shortage increases NAD(+) biosynthesis and SIRT activity but reduces PARP activity in animals. Effects of energy balance on these pathways in humans are unknown. OBJECTIVE: We compared NAD(+)/SIRT pathway expressions and PARP activities in sc adipose tissue (SAT) between lean and obese subjects and investigated their change in the obese subjects during a 12-month weight loss. DESIGN, SETTING AND PARTICIPANTS: SAT biopsies were obtained from 19 clinically healthy obese subjects (mean ± SE body mass index, 34.6 ± 2.7 kg/m(2)) during a weight-loss intervention (0, 5, and 12 mo) and from 19 lean reference subjects (body mass index, 22.7 ± 1.1 kg/m(2)) at baseline. MAIN OUTCOME MEASURES: SAT mRNA expressions of SIRTs 1-7 and the rate-limiting gene in NAD(+) biosynthesis, nicotinamide phosphoribosyltransferase (NAMPT) were measured by Affymetrix, and total PARP activity by ELISA kit. RESULTS: SIRT1, SIRT3, SIRT7, and NAMPT expressions were significantly lower, whereas total PARP activity was increased in obese compared with lean subjects. SIRT1 and NAMPT expressions increased in obese subjects between 0 and 5 months, after a mean weight loss of 11.7%. In subjects who continued to lose weight between 5 and 12 months, SIRT1 expression increased progressively, whereas in subjects with weight regain, SIRT1 reverted to baseline levels. PARP activity significantly decreased in all subjects upon weight loss. CONCLUSIONS: Calorie restriction is an attractive strategy to improve the NAD(+)/SIRT pathway and decrease PARPs in SAT in human obesity.