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3). were unchanged. Thus, we document multiple biochemical changes in the insulin-controlled DM monkey brain that can link DM with the risk of developing AD, including dysregulation of the insulin-signaling pathway, changes in tau phosphorylation, and a decrease in NEP expression in the hippocampus that is coupled with a localized increase in A. SIGNIFICANCE STATEMENT Given that diabetes mellitus (DM) appears to increase the risk of developing Alzheimer’s disease (AD), understanding the mechanisms by which DM promotes AD is important. We statement that DM in a nonhuman primate brain leads to changes in the levels or posttranslational processing of proteins central to AD pathobiology, including tau, amyloid- (A), and the A-degrading protease neprilysin. Additional evidence from this model suggests that alterations in brain insulin signaling occurred that are reminiscent of insulin signaling pathway changes seen in human AD. Thus, in an model highly relevant to humans, we show multiple alterations in the brain resulting from DM that are mechanistically linked to AD risk. = 1 control; = 0 diabetic), 8 weeks (= 3 control; = 3 diabetic), 12 weeks (= 0 control; = 1 diabetic), 16 Zamicastat weeks (= 2 control; = 4 diabetic), and 20 weeks (= 1 control; = 2 diabetic) after STZ or saline treatment. For plasma A ELISA measurements, we analyzed a total of 25 samples, consisting of Ptprc these 17 animals and an additional eight (= 3 control; = 5 diabetic; Kavanagh et al., 2011). These additional eight monkeys were treated Zamicastat identically to the previously explained 17 monkeys, but brain tissue was not available. These monkeys were killed at 4 weeks (= 1 control; = 3 diabetic), 12 weeks (= 1 control; = 2 diabetic), and 20 weeks (= 1 control; = 0 diabetic) after STZ or saline treatment. Diabetic animals received insulin treatment on the day the animals were killed. All collected tissues and terminal blood Zamicastat plasmas were immediately snap-frozen for subsequent biochemical analyses; no tissue was fixed or stored frozen in a cryopreservant. Regional dissections of the hippocampus, frontal cortex, superior temporal cortex, and cerebellum were obtained from frozen coronal-sectioned brain slabs. Antibodies. Full-length APP was detected with the antibody C1/6.1 (Mathews et al., 2002). Antibodies 22C11 (Millipore), JRF/Atot/17 (Morales-Corraliza et al., 2013), and 242 (Nishitomi et al., 2006) recognize soluble APP total (sAPP total: sAPP + sAPP), sAPP, and sAPP, respectively, APP metabolites that we have shown previously to be highly stable in the brain (Morales-Corraliza et al., 2009). Monoclonal antibody 56C6 (CD10; Novocastra) was used to detect neprilysin (NEP). Insulin-degrading enzyme (IDE) was acknowledged with the antibody IDE1 (Qiu et al., 1998; a gift from Dr. Dennis Selkoe, Ann Romney Center for Neurologic Diseases, Harvard Institutes of Medicine, Boston, MA). Endothelin Transforming Enzyme 1 (ECE1) was detected with an antibody from Abgent. Levels of receptor for advanced glycation end products (RAGEs) and low-density lipoprotein receptor-related protein-1 (LRP1) were detected with the antibodies anti-RAGE (Abcam) and anti-LRP1 (American Diagnostica), respectively. Phosphorylated tau was detected using the antibodies PHF-1 (phospho-epitope at Ser396/404; a gift from Dr. Peter Davies, Feinstein Institute for Medical Research, Hofstra North Shore-LIJ School of Medicine, Manhasset, NY; Weaver et al., 2000) and CP13 (phospho-epitope at Ser202; a gift from Dr. Peter Davies). The tau1 antibody (Millipore) was used to recognize tau protein that is not phosphorylated at serines 195, 198, 199, and 202 (Szendrei et al., 1993), and DA9 (a gift from Dr. Peter Davies) detects total tau impartial of its phosphorylation state. Tau kinases/phosphatases extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), phospho-ERK1/2 (Thr202/204), glycogen synthase kinase-3 (GSK3), phospho-GSK3 (Ser9), and protein phosphatase PP2A and PP2B were detected with antibodies from Cell Signaling Technology and p35/p25 and cyclin-dependent kinase 5 (CDK5) were from Santa Cruz Biotechnology. ERK1/2-mediated phosphorylation of tau at both the PHF-1 and CP13 antibody epitope sites.