Multiomics Analyses Identify Proline Endopeptidase-Like Protein As a Key Regulator of Protein Trafficking, a Pathway Underlying Alzheimer's Disease Pathogenesis.

Current treatments for Alzheimer's disease (AD) help reduce symptoms for a limited time but do not treat the underlying pathology. To identify potential therapeutic targets for AD, an integrative network analysis was previously carried out using 364 human postmortem control, mild cognitive impairment, and AD brains. This analysis identified proline endopeptidase-like protein (PREPL), an understudied protein, as a downregulated protein in late-onset AD patients. In this study we investigate the role of PREPL. Analyses of data from human postmortem samples and PREPL knockdown (KD) cells suggest that PREPL expression modulates pathways associated with protein trafficking, synaptic activities, and lipid metabolism. Furthermore, PREPL KD impairs cell proliferation and modulates the structure of vesicles, levels of neuropeptide-processing enzymes, and secretion of neuropeptides. In addition, decrease in PREPL levels leads to changes in the levels of a number of synaptic proteins as well as changes in the levels of secreted amyloid beta (Aß) 42 peptide and Tau phosphorylation. Finally, we report that local decrease in PREPL levels in mouse hippocampus attenuates long-term potentiation, suggesting a role in synaptic plasticity. Together, our results indicate that PREPL affects neuronal function by modulating protein trafficking and synaptic function, an important mechanism of AD pathogenesis. SIGNIFICANCE STATEMENT: Integrative network analysis reveals proline endopeptidase-like protein (PREPL) to be downregulated in human sporadic late-onset Alzheimer's disease brains. Down regulation of PREPL leads to increases in amyloid beta secretion, Tau phosphorylation, and decreases in protein trafficking and long-term potentiation.

γ-Secretase fanning the fire of innate immunity.

Innate immunity is the first line of defense against pathogens, alerting the individual cell and surrounding area to respond to this potential invasion. γ-secretase is a transmembrane protease complex that plays an intricate role in nearly every stage of this innate immune response. Through regulation of pattern recognition receptors (PRR) such as TREM2 and RAGE γ-secretase can modulate pathogen recognition. γ-secretase can act on cytokine receptors such as IFNαR2 and CSF1R to dampen their signaling capacity. While γ-secretase-mediated regulated intramembrane proteolysis (RIP) can further moderate innate immune responses through downstream signaling pathways. Furthermore, γ-secretase has also been shown to be regulated by the innate immune system through cytokine signaling and γ-secretase modulatory proteins such as IFITM3 and Hif-1α. This review article gives an overview of how γ-secretase is implicated in innate immunity and the maintenance of its responses through potentially positive and negative feedback loops.

Hypoxia Inducible Factor-1α binds and activates γ-secretase for Aß production under hypoxia and cerebral hypoperfusion.

Hypoxic-ischemic injury has been linked with increased risk for developing Alzheimer's disease (AD). The underlying mechanism of this association is poorly understood. Here, we report distinct roles for hypoxia-inducible factor-1α (Hif-1α) in the regulation of BACE1 and γ-secretase activity, two proteases involved in the production of amyloid-beta (Aß). We have demonstrated that Hif-1α upregulates both BACE1 and γ-secretase activity for Aß production in brain hypoxia-induced either by cerebral hypoperfusion or breathing 10% O2. Hif-1α binds to γ-secretase, which elevates the amount of active γ-secretase complex without affecting the level of individual subunits in hypoxic-ischemic mouse brains. Additionally, the expression of full length Hif-1α increases BACE1 and γ-secretase activity in primary neuronal culture, whereas a transcriptionally incompetent Hif-1α variant only activates γ-secretase. These findings indicate that Hif-1α transcriptionally upregulates BACE1 and nontranscriptionally activates γ-secretase for Aß production in hypoxic-ischemic conditions. Consequently, Hif-1α-mediated Aß production may be an adaptive response to hypoxic-ischemic injury, subsequently leading to increased risk for AD. Preventing the interaction of Hif-1α with γ-secretase may therefore be a promising therapeutic strategy for AD treatment.

Salvianolic Acid A Protects Against Diabetic Nephropathy through Ameliorating Glomerular Endothelial Dysfunction via Inhibiting AGE-RAGE Signaling.

BACKGROUND/AIMS: Glomerular endothelium dysfunction leads to the progression of renal architectonic and functional abnormalities in early-stage diabetic nephropathy (DN). Advanced glycation end products (AGEs) and receptor for AGEs (RAGE) are proved to play important roles in diabetic nephropathy. This study investigated the role of Salvianolic acid A (SalA) on early-stage DN and its possible underlying mechanism. METHODS: In vitro AGEs formation and breaking rate were measured to illustrate the effect of SalA on AGEs. Type 2 diabetic nephropathy rats were induced by high-fat diet and low-dose streptozocin (STZ). After eight-week treatment with SalA 1 mg/kg/day, 24h-urine protein, creatinine clearance was tested and renal structural injury was assessed by PAS and PASM staining. Primary glomerular endothelial cell permeability was evaluated after exposed to AGEs. AGEs-induced RhoA/ROCK and subsequently activated disarrange of cytoskeleton were assessed by western blot and immunofluorescence. RESULTS: Biochemical assay and histological examination demonstrated that SalA markedly reduced endothelium loss and glomerular hyperfiltration, suppressed glomerular hypertrophy and mesangial matrix expansion, eventually reduced urinary albumin and ameliorated renal function. Further investigation suggested that SalA exerted its renoprotective effects through inhibiting AGE-RAGE signaling. It not only inhibited formation of AGEs and increased its breaking in vitro, but also reduced AGEs accumulation in vivo and downregulated RAGE expression. SalA restored glomerular endothelial permeability through suppressing AGEs-induced rearrangement of actin cytoskeleton via AGE-RAGE-RhoA/ ROCK pathway. Moreover, SalA attenuated oxidative stress induced by AGEs, subsequently alleviated inflammation and restored the disturbed autophagy in glomerular endothelial cell and diabetic rats via AGE-RAGE-Nox4 axis. CONCLUSION: Our study indicated that SalA restored glomerular endothelial function and alleviated renal structural deterioration through inhibiting AGE-RAGE, thus effectively ameliorated early-stage diabetic nephropathy. SalA might be a promising therapeutic agent for the treatment of diabetic nephropathy.

Puerarin Mitigates Diabetic Hepatic Steatosis and Fibrosis by Inhibiting TGF-ß Signaling Pathway Activation in Type 2 Diabetic Rats.

Lipid metabolism disorder and inflammation are essential promoters in pathogenesis of liver injury in type 2 diabetes. Puerarin (PUR) has been reported to exert beneficial effects on many diabetic cardiovascular diseases and chemical-induced liver injuries, but its effects on diabetic liver injury and its mechanism are still unclear. The current study was designed to explore the therapeutic effect and mechanism of PUR on liver injury in a type 2 diabetic rat model induced by a high-fat diet combined with low-dose streptozotocin. The diabetic rats were treated with or without PUR (100 mg/kg/day) by gavaging for 8 weeks, and biochemical and histological changes in liver were examined. Results showed that treatment with PUR significantly attenuated hepatic steatosis by regulating blood glucose and ameliorating lipid metabolism disorder. Liver fibrosis was relieved by PUR treatment. PUR inhibited oxidative stress and inflammation which was associated with inactivation of NF-κB signaling, thereby blocking the upregulation of proinflammatory cytokines (IL-1ß, TNF-α) and chemokine (MCP-1). This protection of PUR on diabetic liver injury is possibly related with inhibition on TGF-ß/Smad signaling. In conclusion, the present study provides evidence that PUR attenuated type 2 diabetic liver injury by inhibiting NF-κB-driven liver inflammation and the TGF-ß/Smad signaling pathway.