A decrease in NAD+ contributes to the loss of osteoprogenitors and bone mass with aging.

Age-related osteoporosis is caused by a deficit in osteoblasts, the cells that secrete bone matrix. The number of osteoblast progenitors also declines with age associated with increased markers of cell senescence. The forkhead box O (FoxO) transcription factors attenuate Wnt/ß-catenin signaling and the proliferation of osteoprogenitors, thereby decreasing bone formation. The NAD+-dependent Sirtuin1 (Sirt1) deacetylates FoxOs and ß-catenin in osteoblast progenitors and, thereby, increases bone mass. However, it remains unknown whether the Sirt1/FoxO/ß-catenin pathway is dysregulated with age in osteoblast progenitors. We found decreased levels of NAD+ in osteoblast progenitor cultures from old mice, associated with increased acetylation of FoxO1 and markers of cell senescence. The NAD+ precursor nicotinamide riboside (NR) abrogated FoxO1 and ß-catenin acetylation and several marker of cellular senescence, and increased the osteoblastogenic capacity of cells from old mice. Consistent with these effects, NR administration to C57BL/6 mice counteracted the loss of bone mass with aging. Attenuation of NAD+ levels in osteoprogenitor cultures from young mice inhibited osteoblastogenesis in a FoxO-dependent manner. In addition, mice with decreased NAD+ in cells of the osteoblast lineage lost bone mass at a young age. Together, these findings suggest that the decrease in bone formation with old age is due, at least in part, to a decrease in NAD+ and dysregulated Sirt1/FoxO/ß-catenin pathway in osteoblast progenitors. NAD+ repletion, therefore, represents a rational therapeutic approach to skeletal involution.

The maize α-zein promoter can be utilized as a strong inducer of cellulase enzyme expression in maize kernels.

Expression of recombinant proteins in plants is a technology for producing vaccines, pharmaceuticals and industrial enzymes. For the past several years, we have produced recombinant proteins in maize kernels using only the embryo, primarily driving expression of foreign genes with the maize globulin-1 promoter. Although strong expression is obtained, these lines use only 10-12% of the seed tissue. If strong embryo expression could be combined with strong endosperm expression, much more recombinant protein could be recovered from a set amount of seed biomass. In this study, we tested three endosperm promoters for expression of a cellulase gene. Promoters tested were rice globulin and glutelin promoters and a maize 19 kDa α-zein promoter. The rice promoters were used in two tandem expression constructs as well. Although the rice promoters were active in producing stable amounts of cellulase, the α-zein promoter was by far the most effective: as much as 9% of total soluble protein was recovered from seed of several independent events and plants. One or two inserts were detected by Southern blot in several lines, indicating that copy number did not appear to be responsible for the differences in protein accumulation. Tissue print analysis indicated that expression was primarily in the endosperm.

The Role of FoxOs in Bone Health and Disease.

Recent studies with murine models of cell-specific loss- or gain-of-function of FoxOs have provided novel insights into the function and signaling of these transcription factors on the skeleton. They have revealed that FoxO actions in chondrocytes are critical for normal skeletal development, and FoxO actions in cells of the osteoclast or osteoblast lineage greatly influence bone resorption and formation and, consequently, bone mass. FoxOs also act in osteoblast progenitors to inhibit Wnt signaling and bone formation. Additionally, FoxOs decrease bone resorption via direct antioxidant effects on osteoclasts and upregulation of the antiosteoclastogenic cytokine OPG in cells of the osteoblast lineage. Deacetylation of FoxOs by the NAD-dependent histone deacetylase Sirt1 in both osteoblasts and osteoclasts stimulates bone formation and inhibits bone resorption, making Sirt1 activators promising therapeutic agents for diseases of low bone mass. In this chapter, we review these advances and discuss their implications for the pathogenesis and treatment of estrogen deficiency-, Type 1 diabetes-, and age-related osteoporosis.

A role for hippocampal PSA-NCAM and NMDA-NR2B receptor function in flavonoid-induced spatial memory improvements in young rats.

The increase in incidence and prevalence of neurodegenerative diseases highlights the need for a more comprehensive understanding of how food components may affect neural systems. In particular, flavonoids have been recognized as promising agents capable of influencing different aspects of synaptic plasticity resulting in improvements in memory and learning in both animals and humans. Our previous studies highlight the efficacy of flavonoids in reversing memory impairments in aged rats, yet little is known about the effects of these compounds in healthy animals, particularly with respect to the molecular mechanisms by which flavonoids might alter the underlying synaptic modifications responsible for behavioral changes. We demonstrate that a 3-week intervention with two dietary doses of flavonoids (Dose I: 8.7 mg/day and Dose II: 17.4 mg/day) facilitates spatial memory acquisition and consolidation (24 recall) (p < 0.05) in young healthy rats. We show for the first time that these behavioral improvements are linked to increased levels in the polysialylated form of the neural adhesion molecule (PSA-NCAM) in the dentate gyrus (DG) of the hippocampus, which is known to be required for the establishment of durable memories. We observed parallel increases in hippocampal NMDA receptors containing the NR2B subunit for both 8.7 mg/day (p < 0.05) and 17.4 mg/day (p < 0.001) doses, suggesting an enhancement of glutamate signaling following flavonoid intervention. This is further strengthened by the simultaneous modulation of hippocampal ERK/CREB/BDNF signaling and the activation of the Akt/mTOR/Arc pathway, which are crucial in inducing changes in the strength of hippocampal synaptic connections that underlie learning. Collectively, the present data supports a new role for PSA-NCAM and NMDA-NR2B receptor on flavonoid-induced improvements in learning and memory, contributing further to the growing body of evidence suggesting beneficial effects of flavonoids in cognition and brain health.

Captodiamine, a putative antidepressant, enhances hypothalamic BDNF expression in vivo by synergistic 5-HT2c receptor antagonism and sigma-1 receptor agonism.

The putative antidepressant captodiamine is a 5-HT2c receptor antagonist and agonist at sigma-1 and D3 dopamine receptors, exerts an anti-immobility action in the forced swim paradigm, and enhances dopamine turnover in the frontal cortex. Captodiamine has also been found to ameliorate stress-induced anhedonia, reduce the associated elevations of hypothalamic corticotrophin-releasing factor (CRF) and restore the reductions in hypothalamic BDNF expression. Here we demonstrate chronic administration of captodiamine to have no significant effect on hypothalamic CRF expression through sigma-1 receptor agonism; however, both sigma-1 receptor agonism or 5-HT2c receptor antagonism were necessary to enhance BDNF expression. Regulation of BDNF expression by captodiamine was associated with increased phosphorylation of transcription factor CREB and mediated through sigma-1 receptor agonism but blocked by 5-HT2c receptor antagonism. The existence of two separate signalling pathways was confirmed by immunolocalisation of each receptor to distinct cell populations in the paraventricular nucleus of the hypothalamus. Increased BDNF induced by captodiamine was also associated with enhanced expression of synapsin, but not PSD-95, suggesting induction of long-term structural plasticity between hypothalamic synapses. These unique features of captodiamine may contribute to its ability to ameliorate stress-induced anhedonia as the hypothalamus plays a prominent role in regulating HPA axis activity.