Hong Qing

Hypoxia facilitates Alzheimer's disease pathogenesis by up-regulating BACE1 gene expression

The molecular mechanism underlying the pathogenesis of the majority of cases of sporadic Alzheimers disease (AD) is unknown. A history of stroke was found to be associated with development of some AD cases, especially in the presence of vascular risk factors. Reduced cerebral perfusion is a common vascular component among AD risk factors, and hypoxia is a direct consequence of hypoperfusion. Previously we showed that expression of the β-site β-amyloid precursor protein (APP) cleavage enzyme 1 (BACE1) gene BACE1 is tightly controlled at both the transcriptional and translational levels and that increased BACE1 maturation contributes to the AD pathogenesis in Downs syndrome. Here we have identified a functional hypoxia-responsive element in the BACE1 gene promoter. Hypoxia up-regulated β-secretase cleavage of APP and amyloid-β protein (Aβ) production by increasing BACE1 gene transcription and expression both in vitro and in vivo. Hypoxia treatment markedly increased Aβ deposition and neuritic plaque formation and potentiated the memory deficit in Swedish mutant APP transgenic mice. Taken together, our results clearly demonstrate that hypoxia can facilitate AD pathogenesis, and they provide a molecular mechanism linking vascular factors to AD. Our study suggests that interventions to improve cerebral perfusion may benefit AD patients.

Valproic acid inhibits Aβ production, neuritic plaque formation, and behavioral deficits in Alzheimer's disease mouse models

Neuritic plaques in the brains are one of the pathological hallmarks of Alzheimers disease (AD). Amyloid β-protein (Aβ), the central component of neuritic plaques, is derived from β-amyloid precursor protein (APP) after β- and γ-secretase cleavage. The molecular mechanism underlying the pathogenesis of AD is not yet well defined, and there has been no effective treatment for AD. Valproic acid (VPA) is one of the most widely used anticonvulsant and mood-stabilizing agents for treating epilepsy and bipolar disorder. We found that VPA decreased Aβ production by inhibiting GSK-3β–mediated γ-secretase cleavage of APP both in vitro and in vivo. VPA treatment significantly reduced neuritic plaque formation and improved memory deficits in transgenic AD model mice. We also found that early application of VPA was important for alleviating memory deficits of AD model mice. Our study suggests that VPA may be beneficial in the prevention and treatment of AD.

Valproic acid inhibits Ab production, neuritic plaque formation, and behavioral deficits in Alzheimer's disease mouse models

Qing et al. 2008. J. Exp. Med. doi:10.1084/jem.20081588 [OpenUrl][1][Abstract/FREE Full Text][2] [1]: {openurl}?query=rft_id%253Dinfo%253Adoi%252F10.1084%252Fjem.20081588%26rft_id%253Dinfo%253Apmid%252F18955571%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%

Transcriptional Regulation of BACE1, the β-Amyloid Precursor Protein β-Secretase, by Sp1

ABSTRACT Proteolytic processing of the β-amyloid precursor protein (APP) at the β site is essential to generate Aβ. BACE1, the major β-secretase involved in cleaving APP, has been identified as a type 1 membrane-associated aspartyl protease. We have cloned a 2.1-kb fragment upstream of the human BACE1 gene and identified key regions necessary for promoter activity. BACE1 gene expression is controlled by a TATA-less promoter. The region of bp −619 to +46 is the minimal promoter to control the transcription of the BACE1 gene. Several putative cis-acting elements, such as a GC box, HSF-1, a PU box, AP1, AP2, and lymphokine response element, are found in the 5′ flanking region of the BACE1 gene. Transcriptional activation and gel shift assays demonstrated that the BACE1 promoter contains a functional Sp1 response element, and overexpression of the transcription factor Sp1 potentiates BACE gene expression and APP processing to generate Aβ. Furthermore, Sp1 knockout reduced BACE1 expression. These results suggest that BACE1 gene expression is tightly regulated at the transcriptional level and that the transcription factor Sp1 plays an important role in regulation of BACE1 to process APP generating Aβ in Alzheimers disease.

Oxidative stress potentiates BACE1 gene expression and Aβ generation

Summary.Alzheimer’s Disease (AD) is the most common neurodegenerative disorder leading to dementia and its prevalence increases with age. The pathological features of AD are characterized by the β-amyloid protein (Aβ) deposits in the core of neuritic plaques and abnormal neurofibrillary tangles in the brain of AD patients. BACE1 is the major β-secretase to cleave the β-amyloid precursor protein (APP) to generate Aβ. Oxidative stress has been shown to affect Aβ generation in the AD pathogenesis and the mechanism of such effect is unknown. In this report we generated a novel promoterless enhanced green fluorescent protein (EGFP) reporter gene cloning vector and cloned a 1.9-kb BACE1 gene promoter fragment in this vector. The BACE1 promoter fragment can efficiently activate EGFP or luciferase gene transcription. Oxidative stress induced by hydrogen peroxide resulted in significant increase in the BACE1 promoter activity. Furthermore, hydrogen peroxide treatment facilitated β-secretase activity and Aβ generation. Thus, upregulation of BACE1 transcription by oxidative stress may contribute to the pathogenesis of Alzheimer’s disease.

Degradation of BACE by the ubiquitin-proteasome pathway

The amyloid β protein (Aβ) is derived from β‐amyloid precursor protein (APP). Cleavage of APP by β‐secretase generates a C‐terminal fragment (APPCTFβ or C99), which is subsequently cleaved by γ‐secretase to produce Aβ. BACE (or BACE1), the major β‐secretase involved in cleaving APP, has been identified as a Type 1 membrane‐associated aspartyl protease. In this study, we found that treatment with proteasome inhibitors resulted in an increase in APP C99 levels, suggesting that APP processing at the β‐secretase site may be affected by the ubiquitin‐proteasome pathway. To investigate whether the degradation of BACE is mediated by the proteasome pathway, cells stably transfected with BACE were treated with lactacystin. We found that BACE protein degradation was inhibited by lactacystin in a time‐ and dose‐dependent manner. Non‐proteasome protease inhibitors had no effect on BACE degradation. BACE protein is ubiquitinated. Furthermore, lactacystin increased APP C99 production and Aβ generation. Our data demonstrate that the degradation of BACE proteins and APP processing are regulated by the ubiquitin‐proteasome pathway.

Lrrk2 phosphorylates alpha synuclein at serine 129: Parkinson disease implications

Mutations in the alpha synuclein gene (SNCA) are the most potent cause of autosomal dominant Parkinson disease (PD) while mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common cause. We hypothesized that a direct interaction may exist between their protein products. Here we show that full-length Lrrk2 or fragments containing its kinase domain have a significant capacity to phosphorylate recombinant alpha synuclein (Asyn) at serine 129. Such phosphorylated Asyn is the major component of pathological deposits in PD. We further show that the G2019S mutation in Lrrk2, which is the most common genetic determinant of PD, has a significantly greater capacity than wild-type Lrrk2 to phosphorylate Asyn. This suggests that the G2019S mutant protein may cause PD by generating pathological levels of phosphorylated Asyn. Controlling Lrrk2 Asyn phosphokinase activity may be an approach to disease modifying therapy for PD and other synucleinopathies.

Distinct transcriptional regulation and function of the human BACE2 and BACE1 genes

Amyloid β protein (Aβ) is the principal component of neuritic plaques in Alzheimers disease (AD). Aβ is derived from β amyloid precursor protein (APP) by β‐ and γ‐secretases. Beta‐site APP cleaving enzyme 1 (BACE1) has been identified as the major β‐secretase. BACE2 is the homolog of BACE1. The BACE2 gene is on chromosome 21 and has been implicated in the pathogenesis of AD. However, the function of BACE2 in Aβ generation is controversial. Some studies have shown that BACE2 cleaved APP at the β‐site whereas other studies showed it cleaved around the α‐secretase site. To elucidate the involvement of BACE2 in AD pathogenesis, we compared BACE2 and BACE1 gene regulation and their functions in Aβ generation. We cloned and functionally characterized the human BACE2 promoter. The BACE2 gene is controlled by a TATA‐less promoter. Though Sp1 can regulate both BACE1 and BACE2 genes, comparative sequence analysis and transcription factor prediction showed little similarity between the two promoters. BACE1 increased APP cleavage at the β‐site and Aβ production whereas BACE2 did not. Overexpression of BACE2 significantly increased sAPP levels in conditioned media but markedly reduced Aβ production. Knockdown of BACE2 resulted in increased APP C83. Our data indicate that despite being homologous in amino acid sequence, BACE2 and BACE1 have distinct functions and transcriptional regulation. BACE2 is not a β‐secretase, but processes APP within the Aβ domain at a site downstream of the α‐secretase cleavage site. Our data argue against BACE2 being involved in the formation of neuritic plaques in AD.—Sun, X., Wang, Y., Qing, H., Christensen, M. A., Liu, Y., Zhou, W., Tong, Y., Xiao, C., Huang, Y., Zhang, S., Liu, X., Song, W. Distinct transcriptional regulation and function of the human BACE2 and BACE1 genes. FASEB J. 19, 739–749 (2005)

Beta amyloid and hyperphosphorylated tau deposits in the pancreas in type 2 diabetes

Strong epidemiologic evidence suggests an association between Alzheimer disease (AD) and type 2 diabetes. To determine if amyloid beta (Abeta) and hyperphosphorylated tau occurs in type 2 diabetes, pancreas tissues from 21 autopsy cases (10 type 2 diabetes and 11 controls) were analyzed. APP and tau mRNAs were identified in human pancreas and in cultured insulinoma beta cells (INS-1) by RT-PCR. Prominent APP and tau bands were detected by Western blotting in pancreatic extracts. Aggregated Abeta, hyperphosphorylated tau, ubiquitin, apolipoprotein E, apolipoprotein(a), IB1/JIP-1 and JNK1 were detected in Langerhans islets in type 2 diabetic patients. Abeta was co-localized with amylin in islet amyloid deposits. In situ beta sheet formation of islet amyloid deposits was shown by infrared microspectroscopy (SIRMS). LPS increased APP in non-neuronal cells as well. We conclude that Abeta deposits and hyperphosphorylated tau are also associated with type 2 diabetes, highlighting common pathogenetic features in neurodegenerative disorders, including AD and type 2 diabetes and suggesting that Abeta deposits and hyperphosphorylated tau may also occur in other organs than the brain.

Increased BACE1 maturation contributes to the pathogenesis of Alzheimer's disease in Down syndrome

Almost all Down syndrome (DS) patients develop characteristic Alzheimers disease (AD) neuropathology, including neuritic plaques and neurofibrillary tangles, after middle age. The mechanism underlying AD neuropathology in DS has been unknown. Aβ is the central component of neuritic plaques and is generated from APP by cleavage by the β‐ and γ‐secretases. Here we show that β‐secretase activity is markedly elevated in DS. The ratio of mature to immature forms of BACE1 is altered in DS. DS has significantly higher levels of mature BACE1 proteins in Golgi than normal controls. Time‐lapse live image analysis showed that BACE1 proteins were predominantly immobile in Golgi in DS cells, while they underwent normal trafficking in controls. Thus, overproduction of Aβ in DS is caused by abnormal BACE1 protein trafficking and maturation. Our results provide a novel molecular mechanism by which AD develops in DS and support the therapeutic potential of inhibiting BACE1 in AD and DS.—Sun, X., Tong, Y., Qing, H., Chen, C‐H., Song, W. Increased BACE1 maturation contributes to Alzheimers disease pathogenesis in Down syndrome. FASEB J. 20, 1361–1368 (2006)