SummaryAging is a result of gradual and overall functional deteriorations across the body; however, it is unknown if an individual tissue works to primarily mediate aging progress and lifespan control. Here we found that the hypothalamus is important for the development of whole-body aging in mice, and the underlying basis involves hypothalamic immunity mediated by IKKβ/NF-κB and related microglia-neuron immune crosstalk. Several interventional models were developed showing that aging retardation and lifespan extension are achieved in mice through preventing against aging-related hypothalamic or brain IKKβ/NF-κB activation. Mechanistic studies further revealed that IKKβ/NF-κB inhibits GnRH to mediate aging-related hypothalamic GnRH decline, and GnRH treatment amends aging-impaired neurogenesis and decelerates aging. In conclusion, the hypothalamus has a programmatic role in aging development via immune-neuroendocrine integration, and immune inhibition or GnRH restoration in the hypothalamus/brain represent two potential strategies for optimizing lifespan and combating aging-related health problems.

The brain, in particular the hypothalamus, plays a role in regulating glucose homeostasis; however, it remains unclear if the brain is causally involved in diabetic development. Here, we identified that hypothalamic TGF-β is excessive under conditions of not only obesity but aging, which are two general etiological factors of diabetes. Pharmacological and genetic approaches consistently revealed that brain TGF-β excess caused hyperglycemia and glucose intolerance in a body weight-independent manner. Cell-specific genetic models demonstrated that astrocytes are responsible for brain TGF-β excess, and POMC neurons are crucial for the pro-diabetic effect of TGF-β excess. Mechanistically, TGF-β excess induced hypothalamic RNA stress response to accelerate IκBα mRNA decay, leading to an atypical, mRNA metabolism-driven hypothalamic NF-κB activation which links obesity as well as aging to hypothalamic inflammation. In conclusion, brain TGF-β excess and induction of RNA stress response and hypothalamic inflammation are important for the pro-diabetic effects of obesity or aging.

␥-Secretase activity is associated with a presenilin (PS)-containing macromolecular complex. Whether PS contains the active site of ␥-secretase has been controversial. One challenge is to find PS that is engaged in the active ␥-secretase complex at the cell surface, where some substrates appear to be processed. In this study, we developed an intact cell photolabeling technique that allows the direct visualization of active ␥-secretase at the cell surface. We demonstrated that active ␥-secretase is present in the plasma membrane. Moreover, the PS1 heterodimer is specifically photolabeled at the cell surface by a potent inhibitor that binds to only the active ␥-secretase. We also explored the cellular processing sites of ␥-secretase for amyloid precursor protein (APP) and Notch by using small molecular probes. MRL631, a ␥-secretase inhibitor that is unable to penetrate the cell membrane, significantly blocks ␥-secretase-mediated Notch cleavage but has little effect on APP processing. These results indicate that Notch is processed at the cell surface and that the majority of APP is processed by intracellular ␥-secretase. Furthermore, the fact that inhibitors first target ␥-secretase in the plasma membrane for Notch processing, and not for APP, will have important implications for drug development to treat Alzheimer's disease and cancer.intact cell photolabeling ͉ intramembrane protease ͉ presenilin

Mutation of the amyloid precursor protein (APP), presenilin-1, or presenilin-2 results in the development of early onset autosomal dominant forms of Alzheimer disease (AD). These mutations lead to an increased A␤42/A␤40 ratio that correlates with the onset of disease. However, it remains unknown how these mutations affect ␥-secretase, a protease that generates the termini of A␤40 and A␤42. Here we have determined the reaction mechanism of ␥-secretase with wild type and three mutated APP substrates. Our findings indicate that despite the overall outcome of an increased A␤42/A␤40 ratio, these mutations each display rather distinct reactivity to ␥-secretase. Intriguingly, we found that the ratio of A␤42/A␤40 is variable with substrate concentration; increased substrate concentrations result in higher ratios of A␤42/A␤40. Moreover, we demonstrated that reduction of ␥-secretase substrate concentration by BACE1 inhibition in cells decreased the A␤42/A␤40 ratio. This study indicates that biological factors affecting targets such as BACE1 and APP, which ultimately cause an increased concentration of ␥-secretase substrate, can augment the A␤42/A␤40 ratio and may play a causative role in sporadic AD. Therefore, strategies lowering the A␤42/A␤40 ratio through partial reduction of ␥-secretase substrate production may introduce a practical therapeutic modality for treatment of AD.␥-Secretase cleaves the amyloid precursor protein (APP) to generate the C termini of ␤-amyloid (A␤) 2 peptides, generally 40 or 42 amino acids in length (A␤40 and A␤42, respectively). A␤ peptides are believed to be a major causative factor in the pathogenesis of Alzheimer disease (AD) (1). A␤42 is more prone to aggregation than A␤40 (2), and therefore biological or environmental factors that promote increased A␤42 production accelerate the pathological cascade leading to AD. Expression of A␤42, rather than A␤40, in Drosophila and mice leads to the formation of A␤ plaques (3, 4). Furthermore, mouse model studies suggest that the ratio of A␤42/A␤40, rather than total amount of A␤, correlates with the load of characteristic AD plaques in the brain (5, 6). Moreover, evidence suggests A␤40 may play a beneficial role in that it antagonizes A␤42 aggregation (5, 6). Therefore, inhibition of ␥-secretase activity that specifically generates A␤42 or reduction of the Ab42/A␤40 ratio would be an appealing strategy for treatment of AD. However, despite intensive studies on ␥-secretase, the mechanism of cleavage specificity for ␥-secretase is still unknown.APP was the first gene found to be linked with inherited AD (7). Each mutation surrounding the ␥-secretase cleavage site appears to alter the production of A␤40 and A␤42. Suzuki et al. (8) demonstrated that mutating APP at Val-46 to Phe or Ile increased the ratio of secreted A␤42 to A␤40 in transfected cells. An increased ratio of A␤42/A␤40 was also observed with other mutations (9 -11). De Jonghe et al. (9) found certain mutations enhanced the stability of the ␥-secretase substrates known as C-terminal fragm...

The ␥-secretase complex, consisting of presenilins (PS), nicastrin (NCT), APH-1, and PEN-2, catalyzes the intramembranous proteolysis of truncated ␤-amyloid precursor protein (APP) and Notch derivatives to generate the APP intracellular domain (AICD) and Notch intracellular domain (NICD), respectively. To examine the intracellular sites in which active ␥-secretase resides, we expressed NCT variants harboring either an endoplasmic reticulum (ER) retention signal (NCT-ER) or a trans-Golgi network (TGN) targeting motif (NCT-TGN) along with PS1, APH-1, and PEN-2 and examined ␥-secretase activity in these settings. In cells expressing NCT-ER and the other components, PS1 fragments hyperaccumulated, but AICD levels were not elevated. On the other hand, upon coexpression of an ER-retained APP variant or a constitutionally active Notch mutant, N⌬E, we observed enhanced production of AICD or NICD, respectively, in cells expressing NCT-ER. Moreover, we show that membranes from cells expressing NCT-ER, NCT-TGN, or NCT-WT contain identical levels of PS1 derivatives that can be photoaffinity cross-linked to a biotinylated, benzophenone-derivatized ␥-secretase inhibitor. Finally, our cell-free ␥-secretase assays revealed nearly equivalent ␥-secretase activities in cells expressing PS1, APH-1, PEN-2, and either NCT-WT or NCT-ER. Taken together, we interpret these findings as suggesting that active ␥-secretase complex is generated in the early compartments of the secretory pathway but that these complexes are transported to late compartments in which substrates are encountered and subsequently processed within respective transmembrane segments.