Physiological ß-amyloid clearance by the liver and its therapeutic potential for Alzheimer's disease.

Cerebral amyloid-ß (Aß) accumulation due to impaired Aß clearance is a pivotal event in the pathogenesis of Alzheimer's disease (AD). Considerable brain-derived Aß is cleared via transporting to the periphery. The liver is the largest organ responsible for the clearance of metabolites in the periphery. Whether the liver physiologically clears circulating Aß and its therapeutic potential for AD remains unclear. Here, we found that about 13.9% of Aß42 and 8.9% of Aß40 were removed from the blood when flowing through the liver, and this capacity was decreased with Aß receptor LRP-1 expression down-regulated in hepatocytes in the aged animals. Partial blockage of hepatic blood flow increased Aß levels in both blood and brain interstitial fluid. The chronic decline in hepatic Aß clearance via LRP-1 knockdown specific in hepatocytes aggravated cerebral Aß burden and cognitive deficits, while enhancing hepatic Aß clearance via LRP-1 overexpression attenuated cerebral Aß deposition and cognitive impairments in APP/PS1 mice. Our findings demonstrate that the liver physiologically clears blood Aß and regulates brain Aß levels, suggesting that a decline of hepatic Aß clearance during aging could be involved in AD development, and hepatic Aß clearance is a novel therapeutic approach for AD.

Blood cell-produced amyloid-ß induces cerebral Alzheimer-type pathologies and behavioral deficits.

It is traditionally believed that cerebral amyloid-beta (Aß) deposits are derived from the brain itself in Alzheimer's disease (AD). Peripheral cells such as blood cells also produce Aß. The role of peripherally produced Aß in the pathogenesis of AD remains unknown. In this study, we established a bone marrow transplantation model to investigate the contribution of blood cell-produced Aß to AD pathogenesis. We found that bone marrow cells (BMCs) transplanted from APPswe/PS1dE9 transgenic mice into wild-type (Wt) mice at 3 months of age continuously expressed human Aß in the blood, and caused AD phenotypes including Aß plaques, cerebral amyloid angiopathy (CAA), tau hyperphosphorylation, neuronal degeneration, neuroinflammation, and behavioral deficits in the Wt recipient mice at 12 months after transplantation. Bone marrow reconstitution in APPswe/PS1dE9 mice with Wt-BMCs at 3 months of age reduced blood Aß levels, and alleviated brain Aß burden, neuronal degeneration, neuroinflammation, and behavioral deficits in the AD model mice at 12 months after transplantation. Our study demonstrated that blood cell-produced Aß plays a significant role in AD pathogenesis, and the elimination of peripheral production of Aß can decrease brain Aß deposition and represents a novel therapeutic approach for AD.

Physiological clearance of amyloid-beta by the kidney and its therapeutic potential for Alzheimer's disease.

Amyloid-ß (Aß) accumulation in the brain is a pivotal event in the pathogenesis of Alzheimer's disease (AD), and its clearance from the brain is impaired in sporadic AD. Previous studies suggest that approximately half of the Aß produced in the brain is cleared by transport into the periphery. However, the mechanism and pathophysiological significance of peripheral Aß clearance remain largely unknown. The kidney is thought to be responsible for Aß clearance, but direct evidence is lacking. In this study, we investigated the impact of unilateral nephrectomy on the dynamic changes in Aß in the blood and brain in both humans and animals and on behavioural deficits and AD pathologies in animals. Furthermore, the therapeutic effects of the diuretic furosemide on Aß clearance via the kidney were assessed. We detected Aß in the kidneys and urine of both humans and animals and found that the Aß level in the blood of the renal artery was higher than that in the blood of the renal vein. Unilateral nephrectomy increased brain Aß deposition; aggravated AD pathologies, including Tau hyperphosphorylation, glial activation, neuroinflammation, and neuronal loss; and aggravated cognitive deficits in APP/PS1 mice. In addition, chronic furosemide treatment reduced blood and brain Aß levels and attenuated AD pathologies and cognitive deficits in APP/PS1 mice. Our findings demonstrate that the kidney physiologically clears Aß from the blood, suggesting that facilitation of Aß clearance via the kidney represents a novel potential therapeutic approach for AD.

Rejuvenation of peripheral immune cells attenuates Alzheimer's disease-like pathologies and behavioral deficits in a mouse model.

Immunosenescence contributes to systematic aging and plays a role in the pathogenesis of Alzheimer's disease (AD). Therefore, the objective of this study was to investigate the potential of immune rejuvenation as a therapeutic strategy for AD. To achieve this, the immune systems of aged APP/PS1 mice were rejuvenated through young bone marrow transplantation (BMT). Single-cell RNA sequencing revealed that young BMT restored the expression of aging- and AD-related genes in multiple cell types within blood immune cells. The level of circulating senescence-associated secretory phenotype proteins was decreased following young BMT. Notably, young BMT resulted in a significant reduction in cerebral Aß plaque burden, neuronal degeneration, neuroinflammation, and improvement of behavioral deficits in aged APP/PS1 mice. The ameliorated cerebral amyloidosis was associated with an enhanced Aß clearance of peripheral monocytes. In conclusion, our study provides evidence that immune system rejuvenation represents a promising therapeutic approach for AD.

Associations of Blood and Cerebrospinal Fluid Aß and tau Levels with Renal Function.

Amyloid ß (Aß) and tau play pivotal roles in the pathogenesis of Alzheimer's disease (AD). Previous studies have shown that brain-derived Aß and tau can be cleared through transport into the periphery, and the kidneys may be vital organs involved in the clearance of Aß and tau. However, the effects of deficiency in the clearance of Aß and tau by the kidneys on brain AD-type pathologies in humans remain largely unknown. In this study, we first recruited 41 patients with chronic kidney disease (CKD) and 40 age- and sex-matched controls with normal renal function to analyze the associations of the estimated glomerular filtration rate (eGFR) with plasma Aß and tau levels. To analyze the associations of eGFR with cerebrospinal fluid (CSF) AD biomarkers, we recruited 42 cognitively normal CKD patients and 150 cognitively normal controls with CSF samples. Compared with controls with normal renal function, CKD patients had higher plasma levels of Aß40, Aß42 and total tau (T-tau), lower CSF levels of Aß40 and Aß42 and higher levels of CSF T-tau/Aß42 and phosphorylated tau (P-tau)/Aß42. Plasma Aß40, Aß42, and T-tau levels were negatively correlated with eGFR. In addition, eGFR was negatively correlated with CSF levels of T-tau, T-tau/Aß42, and P-tau/Aß42 but positively correlated with Mini-Mental State Examination (MMSE) scores. Thus, this study showed that the decline in renal function was correlated with abnormal AD biomarkers and cognitive decline, which provides human evidence that renal function may be involved in the pathogenesis of AD.

The Correlation of Tau Levels with Blood Monocyte Count in Patients with Alzheimer's Disease.

BACKGROUND: Recent studies have shown that monocytes can phagocytize the tau protein, which may ameliorate tau-type pathology in Alzheimer's disease (AD). However, there are few clinical studies on the relationship between monocytes and tau-type pathology in AD patients. OBJECTIVE: We aimed to explore changes in peripheral monocytes and their association with tau protein in AD patients. METHODS: A total of 127 clinically diagnosed AD patients and 100 age- and sex-matched cognitively normal controls were recruited for analysis of the correlation of plasma tau levels with the blood monocyte count. Cerebrospinal fluid (CSF) samples from 46 AD patients and 88 controls were further collected to analyze the correlation of CSF tau and amyloid-ß (Aß) levels with the blood monocyte count. 105 clinically diagnosed mild cognitive impairment (MCI) patients and 149 age- and sex-matched cognitively normal controls were recruited from another cohort for verification. RESULTS: Compared to normal controls, AD patients showed a significant reduction in the blood monocyte count. In addition, the monocyte count of AD patients was negatively correlated with CSF t-tau and p-tau levels but not with plasma tau levels. In normal people, monocyte count lack correlation with tau levels both in plasma and CSF. Monocyte count were not correlated with CSF Aß levels in either group but were negatively correlated with CSF tau/Aß42 levels in the AD group. We had further verified the correlations of monocyte count with CSF tau levels in another cohort. CONCLUSION: This study suggests that monocytes may play an important role in the clearance of tau protein in the brain.

Associations of plasma soluble CD22 levels with brain amyloid burden and cognitive decline in Alzheimer's disease.

CD22 has been suggested to contribute to Alzheimer's disease (AD) pathogenesis by inhibiting microglial amyloid ß (Aß) phagocytosis. Soluble CD22 (sCD22) generated by cleavage from cell membranes may be a marker of inflammation and microglial dysfunction; but alterations of sCD22 levels in AD and their correlation with AD biomarkers remain unclear. Plasma sCD22 levels were measured in cognitively normal non-AD participants and patients with preclinical AD and AD dementia from a Chinese cohort and the Australian Imaging, Biomarkers and Lifestyle Flagship Study of Ageing. Plasma sCD22 levels were elevated in patients with preclinical and dementia AD. Plasma sCD22 levels were negatively correlated with cerebrospinal fluid (CSF) Aß42 levels and Aß42/Aß40, and positively correlated with CSF phosphorylated tau levels and brain Aß burden, but negatively correlated with cognitive function. Moreover, higher plasma sCD22 levels were associated with faster cognitive decline during follow-up. These findings suggest that CD22 plays important roles in AD development, and that sCD22 is a potential biomarker for AD.

The Correlations Between Plasma Fibrinogen With Amyloid-Beta and Tau Levels in Patients With Alzheimer's Disease.

Recent studies show that fibrinogen plays a role in the pathogenesis of Alzheimer's disease (AD), which may be crucial to neurovascular damage and cognitive impairment. However, there are few clinical studies on the relationship between fibrinogen and AD. 59 11C-PiB-PET diagnosed AD patients and 76 age- and gender-matched cognitively normal controls were included to analyze the correlation between plasma ß-amyloid (Aß) and tau levels with fibrinogen levels. 35 AD patients and 76 controls with cerebrospinal fluid (CSF) samples were included to further analyze the correlation between CSF Aß and tau levels with fibrinogen levels. In AD patients, plasma fibrinogen levels were positively correlated with plasma Aß40 and Aß42 levels, and negatively correlated with CSF Aß42 levels. Besides, fibrinogen levels were positively correlated with CSF total tau (t-tau), and phosphorylated tau-181 (p-tau) levels and positively correlated with the indicators of Aß deposition in the brain, such as t-tau/Aß42, p-tau/Aß42 levels. In normal people, fibrinogen levels lack correlation with Aß and tau levels in plasma and CSF. This study suggests that plasma fibrinogen levels are positively correlated with Aß levels in the plasma and brain in AD patients. Fibrinogen may be involved in the pathogenesis of AD.

Amyloid-beta uptake by blood monocytes is reduced with ageing and Alzheimer's disease.

Deficits in the clearance of amyloid ß-protein (Aß) play a pivotal role in the pathogenesis of sporadic Alzheimer's disease (AD). The roles of blood monocytes in the development of AD remain unclear. In this study, we sought to investigate the alterations in the Aß phagocytosis function of peripheral monocytes during ageing and in AD patients. A total of 104 cognitively normal participants aged 22-89 years, 24 AD patients, 25 age- and sex-matched cognitively normal (CN) subjects, 15 Parkinson's disease patients (PD), and 15 age- and sex-matched CN subjects were recruited. The Aß uptake by blood monocytes was measured and its alteration during ageing and in AD patients were investigated. Aß1-42 uptake by monocytes decreased during ageing and further decreased in AD but not in PD patients. Aß1-42 uptake by monocytes was associated with Aß1-42 levels in the blood. Among the Aß uptake-related receptors and enzymes, the expression of Toll-like receptor 2 (TLR2) was reduced in monocytes from AD patients. Our findings suggest that monocytes regulate the blood levels of Aß and might be involved in the development of AD. The recovery of the Aß uptake function by blood monocytes represents a potential therapeutic strategy for AD.

Plasma α-synuclein levels are increased in patients with obstructive sleep apnea syndrome.

OBJECTIVE: Obstructive sleep apnea syndrome (OSAS) is characterized by nocturnal intermittent hypoxemia and can increase the risk of Parkinson's disease. This study aimed to investigate the association between plasma α-synuclein levels and hypoxia in the patients with OSAS. METHODS: We recruited 42 OSAS patients and 46 controls with simple snoring matched for age and gender. OSAS was diagnosed on the basis of the clinical symptoms as well as the nighttime polysomnography. Plasma total α-synuclein and phosphorylated α-synuclein levels were measured by ELISA kits. RESULTS: The OSAS patients had significant higher levels of plasma total α-synuclein and phosphorylated α-synuclein levels. Both of the above indexes were positively correlated with the apnea-hypopnea index and the oxygen desaturation index, while they were negatively correlated with the mean and lowest oxyhemoglobin saturations. INTERPRETATION: This study suggests that chronic intermittent hypoxia can increase the α-synuclein levels, which may contribute to the pathogenesis of Parkinson's disease.

Gut Microbiota Alteration and Its Time Course in a Tauopathy Mouse Model.

Emerging evidence suggests that gut microbiota dysbiosis plays a role in neurodegenerative disorders. However, whether the composition and diversity of the gut microbiota are altered in tauopathies remains largely unknown. This study was aimed to examine the diversity and composition of the gut microbiota in tauopathies, as well as the correlation with pathological changes in the brain. We collected fecal samples from 32 P301L tau transgenic mice and 32 age- and gender-matched littermate mice at different ages. The 16S ribosomal RNA sequencing technique was used to analyze the microbiota composition in feces. Brain tau pathology levels were measured by immunohistochemistry. The diversity and composition of the gut microbiota significantly changed with aging. At the phylum level, the relative abundance of Bacteroidetes was increased, while Firmicutes were decreased in P301L mice compared with that in Wt mice after 3 months of age. In addition, Actinobacteria was decreased in P301L mice at 3 and 6 months of age, meanwhile Tenericutes was decreased in P301L mice at 10 months of age. Moreover, several specific macrobiota were highly associated with the levels of AT8-tau or pT231-tau protein in the brain. Our findings suggest that gut microbiota changed with aging, as well as in the tauopathy mice model. Modulation of the gut microbiota may be a potential strategy for treatment of tauopathy.

The Correlations of Plasma and Cerebrospinal Fluid Amyloid-Beta Levels with Platelet Count in Patients with Alzheimer's Disease.

PURPOSE: Recent study shows that blood-derived amyloid-beta (Aß) can induce cerebral amyloidosis and is involved in the pathogenesis of Alzheimer's disease (AD). The vast majority of blood Aß is generated from platelet. Whether blood Aß levels are associated with the count of platelets remains unknown. METHODS: 58 clinically diagnosed AD patients, 18 11C-PIB-PET diagnosed AD patients, and 61 age- and gender-matched cognitively normal controls were included to analyze the correlation of plasma Aß levels with platelet count. 13 AD patients and 40 controls with cerebrospinal fluid (CSF) samples were included to further analyze the correlation of CSF Aß levels with platelet count. Aß40 and Aß42 levels in plasma and CSF were measured by ELISA kits. RESULTS: The plasma Aß42 level was positively correlated with platelet count in both AD patients and control group, especially in AD patients with positive PIB-PET, while there was no correlation as to Aß40. The CSF Aß levels also had no significant correlation with platelet count. CONCLUSION: It suggests that platelets may be involved in the pathogenesis of AD and become a potential peripheral biomarker for AD.