Caused by the presence of an extra copy of human chromosome 21 (trisomy 21), Down syndrome (DS) is the most common genetic disorder with an incidence of one in 800 live births. DS patients suffer various symptoms, including mental retardation and an early-onset of Alzheimer's disease (AD). The brains of both DS and AD patients show increased amounts of b-amyloid (Ab), which leads to the formation of amyloid plaques, a hallmark of AD pathogenesis (Mann and Esiri 1989). Although the cause of an early-onset AD in DS patients is not clearly understood (Wisniewski et al. 1985), one potential mechanism is overexpression of the gene for b-amyloid precursor protein (APP) located on chromosome 21. Three copies of the APP gene are necessary for DS-affected individuals to develop AD pathology (Prasher et al. 1998). However, this genetic background does not sufficiently account for the full spectrum of pathologies seen in AD patients; over-expres- Abbreviations used: aa, amino acids; AD, Alzheimer's disease; APP, amyloid precursor protein; APPct, C-terminal fragment of APP; Ab, b-amyloid; BACE1, b-secretase APP Cleaving Enzyme 1; DS, Down syndrome; DYRK1A, dual-specificity tyrosine(Y)-phosphorylation regulated kinase 1A; GFP, green fluorescent protein; GST, glutathione S-transferase; NGF, nerve growth factor; p-AICD, phospho-APP intracellular domain; PBS, phosphate-buffered saline; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; TG, transgenic; WT, wild-type; YF, Y321F kinase-inactive mutant. AbstractMost individuals with Down Syndrome (DS) show an earlyonset of Alzheimer's disease (AD), which potentially results from the presence of an extra copy of a segment of chromosome 21. Located on chromosome 21 are the genes that encode b-amyloid (Ab) precursor protein (APP ), a key protein involved in the pathogenesis of AD, and dual-specificity tyrosine(Y)-phosphorylation regulated kinase 1A (DYRK1A ), a proline-directed protein kinase that plays a critical role in neurodevelopment. Here, we describe a potential mechanism for the regulation of AD pathology in DS brains by DYRK1A-mediated phosphorylation of APP. We show that APP is phosphorylated at Thr668 by DYRK1A in vitro and in mammalian cells. The amounts of phospho-APP and Ab are increased in the brains of transgenic mice that over-express the human DYRK1A protein. Furthermore, we show that the amounts of phospho-APP as well as those of APP and DYRK1A are elevated in human DS brains. Taken together, these results reveal a potential regulatory link between APP and DYRK1A in DS brains, and suggest that the overexpression of DYRK1A in DS may play a role in accelerating AD pathogenesis through phosphorylation of APP.

Most individuals with Down syndrome show early onset of Alzheimer disease (AD), resulting from the extra copy of chromosome 21. Located on this chromosome is a gene that encodes the dual specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A). One of the pathological hallmarks in AD is the presence of neurofibrillary tangles (NFTs), which are insoluble deposits that consist of abnormally hyperphosphorylated Tau. Previously it was reported that Tau at the Thr-212 residue was phosphorylated by Dyrk1A in vitro. To determine the physiological significance of this phosphorylation, an analysis was made of the amount of phospho-Thr-212-Tau (pT212) in the brains of transgenic mice that overexpress the human DYRK1A protein (DYRK1A TG mice) that we recently generated. A significant increase in the amount of pT212 was found in the brains of DYRK1A transgenic mice when compared with age-matched littermate controls. We further examined whether Dyrk1A phosphorylates other Tau residues that are implicated in NFTs. We found that Dyrk1A also phosphorylates Tau at Ser-202 and Ser-404 in vitro. Phosphorylation by Dyrk1A strongly inhibited the ability of Tau to promote microtubule assembly. Following this, using mammalian cells and DYRK1A TG mouse brains, it was demonstrated that the amounts of phospho-Ser-202-Tau and phospho-Ser-404-Tau are enhanced when DYRK1A amounts are high. These results provide the first in vivo evidence for a physiological role of DYRK1A in the hyperphosphorylation of Tau and suggest that the extra copy of the DYRK1A gene contributes to the early onset of AD. Down syndrome (DS)3 is the most common genetic disorder with a frequency of 1 in 800 live births, and it is caused by the presence of an extra copy of whole or part of human chromosome 21 (1, 2). DS patients suffer various symptoms, including congenital heart defects, immune and endocrine system defects, mental retardation, and early onset of Alzheimer disease (AD) (3). Both DS and AD patients have pathological hallmarks, amyloid plaques and neurofibrillary tangles (NFTs) that are insoluble deposits made of proteins called ␤-amyloid (A␤) and hyperphosphorylated Tau, respectively (4 -6). Although an early onset AD in DS patients is not clearly understood, one potential mechanism is the presence of three chromosomal copies of ␤-amyloid precursor protein (APP) gene. However, the APP overexpression alone in mice does not show the endosome abnormalities observed in AD-like pathology (7), implying the necessity of additional genes on the chromosome 21 for a full spectrum of AD pathologies.NFTs found in AD are composed of paired helical filaments (PHFs), which are mainly composed of hyperphosphorylated Tau protein (8). To date, more than 30 phosphorylation sites and 7-10 mol of phosphates per mol of Tau have been observed in PHF-Tau (9, 10). Although Tau protein is phosphorylated in vitro by numerous kinases, it is unclear how many kinases actually phosphorylate Tau in vivo. Currently, only glycogen synthase kinase 3␤ (GSK3␤), cyclin-dependent kinas...

Background Researchers have suggested models to predict the risk of postoperative AKI (PO-AKI), but an externally validated risk index that can be practically implemented before patients undergo noncardiac surgery is needed. MethodsWe performed a retrospective observational study of patients without preexisting renal failure who underwent a noncardiac operation ($1 hour) at two tertiary hospitals in Korea. We fitted a proportional odds model for an ordinal outcome consisting of three categories: critical AKI (defined as Kidney Disease Improving Global Outcomes AKI stage $2, post-AKI death, or dialysis within 90 days after surgery), low-stage AKI (defined as PO-AKI events not fulfilling the definition of critical AKI), and no PO-AKI. ResultsThe study included 51,041 patients in a discovery cohort and 39,764 patients in a validation cohort. The Simple Postoperative AKI Risk (SPARK) index included a summation of the integer scores of the following variables: age, sex, expected surgery duration, emergency operation, diabetes mellitus, use of renin-angiotensin-aldosterone inhibitors, baseline eGFR, dipstick albuminuria hypoalbuminemia, anemia, and hyponatremia. The model calibration plot showed tolerable distribution of observed and predicted probabilities in both cohorts. The discrimination power of the SPARK index was acceptable in both the discovery (c-statistic 0.80) and validation (c-statistic 0.72) cohorts. When four SPARK classes were defined on the basis of the sum of the risk scores, the SPARK index and classes fairly reflected the risks of PO-AKI and critical AKI.Conclusions Clinicians may consider implementing the SPARK index and classifications to stratify patients' PO-AKI risks before performing noncardiac surgery.

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