Full-length amyloid precursor protein regulates lipoprotein metabolism and amyloid-β clearance in human astrocytes

Abstract

Mounting evidence suggests that alterations in cholesterol homeostasis are involved in Alzheimer's disease (AD) pathogenesis. Amyloid precursor protein (APP) or multiple fragments generated by proteolytic processing of APP have previously been implicated in the regulation of cholesterol metabolism. However, the physiological function of APP in regulating lipoprotein homeostasis in astrocytes, which are responsible for cholesterol biosynthesis and regulation in the brain, remains unclear. To address this, here we used CRISPR/Cas9 genome editing to generate isogenic APP-knockout (KO) human induced pluripotent stem cells (hiPSCs) and differentiated them into human astrocytes. We found that APP-KO astrocytes have reduced cholesterol and elevated levels of sterol regulatory element-binding protein (SREBP) target gene transcripts and proteins, which were both downstream consequences of reduced lipoprotein endocytosis. To elucidate which APP fragments regulate cholesterol homeostasis and to examine whether familial AD mutations in APP affect lipoprotein metabolism, we analyzed an isogenic allelic series harboring the APP Swedish and APP V717F variants. Only astrocytes homozygous for the APP Swedish (APP) mutation, which had reduced full-length APP (FL APP) due to increased β-secretase cleavage, recapitulated the APP-KO phenotypes. Astrocytic internalization of β-amyloid (Aβ), another ligand for low-density lipoprotein (LDL) receptors, was also impaired in APP-KO and APP astrocytes. Finally, impairing cleavage of FL APP through β-secretase inhibition in APP astrocytes reversed the LDL and Aβ endocytosis defects. In conclusion, FL APP is involved in the endocytosis of LDL receptor ligands and is required for proper cholesterol homeostasis and Aβ clearance in human astrocytes.

Cholesterol Metabolism Is a Druggable Axis that Independently Regulates Tau and Amyloid-β in iPSC-Derived Alzheimer’s Disease Neurons

“…Interestingly, in these APP null neurons, simvastatin still reduced pThr231Tau/tTau in a dose-dependent manner identical to that of its isogenic control lines (Figure 3H). Similarly, simvastatin reduced pThr231Tau/tTau the same in a previously generated isogenic set of NDC (APP wt ) and APP null neurons (CV line 151 and IB6) (Fong et al., 2018) (Figure 3H). Together, these data show that CE regulate both pTau and Aβ, but regulation of pTau by CE is APP- and Aβ-independent.…”

Chromatin establishes an immature version of neuronal protocadherin selection during the naive-to-primed conversion of pluripotent stem cells

“…For astrocytic differentiation, we also followed a protocol previously reported 67 . Briefly, NPCs derived from hiPSC1/4/5/8 were seeded in a 10-cm plate and grown in NPC media containing 20 ng/mL of bFGF (Millipore; GF003AF-MG) to confluency, scraped, and transferred to three uncoated wells of a 6-well plate.…”

Efficacy of the combined use of donepezil with either quetiapine or sodium valproate in patients with Alzheimer's disease with behavioral and psychological symptoms of dementia, and their effects on vascular endothelial growth factors

“…VEGF is a highly biologically active vascular growth promoting factor with neurotrophic, neuroprotective and angiogenic effects ( 25 ). It has been reported ( 26 ) that VEGF and β amyloid protein can promote each other in patients with AD, and β amyloid deposition is the main cause of the degeneration and death of peripheral neurons of senile plaques. The study by Mateo et al ( 27 ) demonstrated that VEGF expression in the serum of patients with AD was significantly decreased, while the study by Kakinuma et al ( 28 ) demonstrated that donepezil promoted cardiovascular growth and VEGF expression in mice.…”