IMPORTANCE Synaptic loss is an early pathologic substrate of Alzheimer disease (AD). Neurogranin is a postsynaptic neuronal protein that has demonstrated utility as a cerebrospinal fluid (CSF) marker of synaptic loss in AD.OBJECTIVE To investigate the diagnostic and prognostic utility of CSF neurogranin levels in a large, well-characterized cohort of individuals with symptomatic AD and cognitively normal controls. DESIGN, SETTING, AND PARTICIPANTSA cross-sectional and longitudinal observational study of cognitive decline in patients with symptomatic AD and cognitively normal controls was performed. Participants were individuals with a clinical diagnosis of early symptomatic AD and cognitively normal controls who were enrolled in longitudinal studies of aging and dementia at the Charles F.

One of the major protein components of the ocular lens, ␣-crystallin, is composed of ␣A and ␣B chain subunits that have structural homology to the family of mammalian small heat shock proteins. Like other small heat shock proteins, ␣-crystallin subunits associate to form large oligomeric aggregates that express chaperone-like activity, as defined by the ability to suppress nonspecific aggregation of proteins destabilized by treatment with a variety of denaturants including heat, UV irradiation, and chemical modification. It has been proposed that age-related loss of sequences at the C terminus of the ␣A chain subunit may be a factor in the pathogenesis of cataract due to diminished capacity of the truncated crystallin to protect against nonspecific aggregation of lens proteins. To evaluate the functional consequences of ␣-crystallin modification, two mutant forms of ␣A subunits were prepared by site-directed mutagenesis. Like wild type (WT), aggregates of ϳ540 kDa were formed from a tryptophan-free ␣A mutant (W9F). When added in stoichiometric amounts, both WT and W9F subunits completely suppressed the heat-induced aggregation of aldose reductase. In contrast, subunits encoded by a truncation mutant in which the Cterminal 17 residues were deleted (R157STOP), despite having spectroscopic properties similar to WT, formed much larger aggregates with a marked reduction in chaperone-like activity. Similar results were observed when the chaperone-like activity was assessed through inhibition of ␥-crystallin aggregation induced by singlet oxygen. These results demonstrate that the structurally conservative substitution of Phe for Trp-9 has a negligible effect on the functional interaction of ␣A subunits, and that deletion of C-terminal sequences from the ␣A subunit results in substantial loss of chaperone-like activity, despite overall preservation of secondary structure.The major components of the mammalian lens fiber cells are the ␣-, ␤-, and ␥-crystallins, which constitute an estimated 35% wet weight of the lens. The crystallins contribute to the transparency and refractive power of the lens by short range interactions among themselves and cytoskeletal elements in a highly concentrated matrix (1-3). ␣-Crystallin is one of the most abundant of the crystallins in mature lens fiber cells. It is a M r ϳ0.6 -1.0 ϫ 10 6 complex composed of two structurally related subunits, designated ␣A and ␣B, which are encoded by genes localized to chromosomes 21 and 11, respectively (4, 5).

The intestinal peptides GLP-1 and GIP potentiate glucosemediated insulin release. Agents that increase GLP-1 action are effective therapies in type 2 diabetes mellitus (T2DM). However, GIP action is blunted in T2DM, and GIP-based therapies have not been developed. Thus, it is important to increase our understanding of the mechanisms of GIP action. We developed mice lacking GIP-producing K cells. Like humans with T2DM, "GIP/DT" animals exhibited a normal insulin secretory response to exogenous GLP-1 but a blunted response to GIP. Pharmacologic doses of xenin-25, another peptide produced by K cells, restored the GIP-mediated insulin secretory response and reduced hyperglycemia in GIP/DT mice. Xenin-25 alone had no effect. Studies with islets, insulin-producing cell lines, and perfused pancreata indicated xenin-25 does not enhance GIP-mediated insulin release by acting directly on the ␤-cell. The in vivo effects of xenin-25 to potentiate insulin release were inhibited by atropine sulfate and atropine methyl bromide but not by hexamethonium. Consistent with this, carbachol potentiated GIP-mediated insulin release from in situ perfused pancreata of GIP/DT mice. In vivo, xenin-25 did not activate c-fos expression in the hind brain or paraventricular nucleus of the hypothalamus indicating that central nervous system activation is not required. These data suggest that xenin-25 potentiates GIP-mediated insulin release by activating non-ganglionic cholinergic neurons that innervate the islets, presumably part of an enteric-neuronal-pancreatic pathway. Xenin-25, or molecules that increase acetylcholine receptor signaling in ␤-cells, may represent a novel approach to overcome GIP resistance and therefore treat humans with T2DM.The entero-insulin axis is a physiologic system composed of peptides secreted from the gastrointestinal tract that play an important role in regulating insulin secretion from pancreatic islet ␤-cells (1, 2). To date, attention has focused on two intestinal peptides, glucagon-like peptide-1 (GLP-1) 2 and glucosedependent insulinotropic polypeptide (GIP). GIP is produced predominantly by intestinal K cells located in the proximal small intestine, whereas GLP-1 is produced primarily by intestinal L-cells present in the distal bowel (3-5). Release of GLP-1 and GIP is controlled by nutrient levels in the lumen of the gut rather than the bloodstream. Both hormones are released into the bloodstream immediately after ingestion of a meal and then potentiate glucose-stimulated insulin release. This increase in insulin secretion has been termed the incretin effect. Importantly, the incretin effect occurs only in the presence of elevated blood glucose and does not cause postprandial hypoglycemia.An increase in circulating GLP-1 activity has significant therapeutic benefit in patients with T2DM (1, 2, 6 -10). Two major classes of drugs that accomplish this goal have recently been introduced into the market with substantial success. Long acting analogs of GLP-1 potentiate glucose-stimulated insulin secretion leadin...

We utilized the budding yeast Saccharomyces cerevisiae as a model to systematically explore physiological roles for yeast and mammalian aldo-keto reductases. Six open reading frames encoding putative aldo-keto reductases were identified when the yeast genome was queried against the sequence for human aldose reductase, the prototypical mammalian aldo-keto reductase. Recombinant proteins produced from five of these yeast open reading frames demonstrated NADPH-dependent reductase activity with a variety of aldehyde and ketone substrates. A triple aldo-keto reductase null mutant strain demonstrated a glucose-dependent heat shock phenotype which could be rescued by ectopic expression of human aldose reductase. Catalytically-inactive mutants of human or yeast aldo-keto reductases failed to effect a rescue of the heat shock phenotype, suggesting that the phenotype results from either an accumulation of one or more unmetabolized aldo-keto reductase substrates or a synthetic deficiency of aldo-keto reductase products generated in response to heat shock stress. These results suggest that multiple aldo-keto reductases fulfill functionally redundant roles in the stress response in yeast.

Xenin-25 (Xen) is a neurotensin-related peptide secreted by a subset of glucose-dependent insulinotropic polypeptide (GIP)-producing enteroendocrine cells. In animals, Xen regulates gastrointestinal function and glucose homeostasis, typically by initiating neural relays. However, little is known about Xen action in humans. This study determines whether exogenously administered Xen modulates gastric emptying and/or insulin secretion rates (ISRs) following meal ingestion. Fasted subjects with normal (NGT) or impaired (IGT) glucose tolerance and Type 2 diabetes mellitus (T2DM; n = 10-14 per group) ingested a liquid mixed meal plus acetaminophen (ACM; to assess gastric emptying) at time zero. On separate occasions, a primed-constant intravenous infusion of vehicle or Xen at 4 (Lo-Xen) or 12 (Hi-Xen) pmol · kg(-1) · min(-1) was administered from zero until 300 min. Some subjects with NGT received 30- and 90-min Hi-Xen infusions. Plasma ACM, glucose, insulin, C-peptide, glucagon, Xen, GIP, and glucagon-like peptide-1 (GLP-1) levels were measured and ISRs calculated. Areas under the curves were compared for treatment effects. Infusion with Hi-Xen, but not Lo-Xen, similarly delayed gastric emptying and reduced postprandial glucose levels in all groups. Infusions for 90 or 300 min, but not 30 min, were equally effective. Hi-Xen reduced plasma GLP-1, but not GIP, levels without altering the insulin secretory response to glucose. Intense staining for Xen receptors was detected on PGP9.5-positive nerve fibers in the longitudinal muscle of the human stomach. Thus Xen reduces gastric emptying in humans with and without T2DM, probably via a neural relay. Moreover, endogenous GLP-1 may not be a major enhancer of insulin secretion in healthy humans under physiological conditions.