Recombinant BRICHOS chaperone domains delivered to mouse brain parenchyma by focused ultrasound and microbubbles are internalized by hippocampal and cortical neurons

The BRICHOS domain is found in human precursor proteins associated with cancer, dementia (Bri2) and amyloid lung disease (proSP-C). Recombinant human (rh) proSP-C and Bri2 BRICHOS domains delay amyloid-β peptide (Aβ) fibril formation and reduce associated toxicity in vitro and their overexpression reduces Aβ neurotoxicity in animal models of Alzheimer's disease. After intravenous administration in wild-type mice, rh Bri2, but not proSP-C, BRICHOS was detected in the brain parenchyma, suggesting that Bri2 BRICHOS selectively bypasses the blood-brain barrier (BBB). Here, our objective was to increase the brain delivery of rh proSP-C (trimer of 18 kDa subunits) and Bri2 BRICHOS (monomer to oligomer of 15 kDa subunits) using focused ultrasound combined with intravenous microbubbles (FUS + MB), which enables targeted and transient opening of the BBB. FUS + MB was targeted to one hemisphere of wild type mice and BBB opening in the hippocampal region was confirmed by magnetic resonance imaging. Two hours after FUS + MB brain histology showed no signs of tissue damage and immunohistochemistry showed abundant delivery to the brain parenchyma in 13 out of 16 cases given 10 mg/kg of proSP-C or Bri2 BRICHOS domains. The Bri2, but not proSP-C BRICHOS domain was detected also in the non-targeted hemisphere. ProSP-C and Bri2 BRICHOS domains were taken up by a subset of neurons in the hippocampus and cortex, and were detected to a minor extent in early endosomes. These results indicate that rh Bri2, but not proSP-C, BRICHOS, can be efficiently delivered into the mouse brain parenchyma and that both BRICHOS domains can be internalized by cell-specific mechanisms.

Current and future treatment of amyloid diseases

There are more than 30 human proteins whose aggregation appears to cause degenerative maladies referred to as amyloid diseases or amyloidoses. These disorders are named after the characteristic cross-β-sheet amyloid fibrils that accumulate systemically or are localized to specific organs. In most cases, current treatment is limited to symptomatic approaches and thus disease-modifying therapies are needed. Alzheimer's disease is a neurodegenerative disorder with extracellular amyloid β-peptide (Aβ) fibrils and intracellular tau neurofibrillary tangles as pathological hallmarks. Numerous clinical trials have been conducted with passive and active immunotherapy, and small molecules to inhibit Aβ formation and aggregation or to enhance Aβ clearance; so far such clinical trials have been unsuccessful. Novel strategies are therefore required and here we will discuss the possibility of utilizing the chaperone BRICHOS to prevent Aβ aggregation and toxicity. Type 2 diabetes mellitus is symptomatically treated with insulin. However, the underlying pathology is linked to the aggregation and progressive accumulation of islet amyloid polypeptide as fibrils and oligomers, which are cytotoxic. Several compounds have been shown to inhibit islet amyloid aggregation and cytotoxicity in vitro. Future animal studies and clinical trials have to be conducted to determine their efficacy in vivo. The transthyretin (TTR) amyloidoses are a group of systemic degenerative diseases compromising multiple organ systems, caused by TTR aggregation. Liver transplantation decreases the generation of misfolded TTR and improves the quality of life for a subgroup of this patient population. Compounds that stabilize the natively folded, nonamyloidogenic, tetrameric conformation of TTR have been developed and the drug tafamidis is available as a promising treatment.

BRI2 ectodomain affects Aβ42 fibrillation and tau truncation in human neuroblastoma cells

Alzheimer's disease (AD) is pathologically characterized by the presence of misfolded proteins such as amyloid beta (Aβ) in senile plaques, and hyperphosphorylated tau and truncated tau in neurofibrillary tangles (NFT). The BRI2 protein inhibits Aβ aggregation via its BRICHOS domain and regulates critical proteins involved in initiating the amyloid cascade, which has been hypothesized to be central in AD pathogenesis. We recently detected the deposition of BRI2 ectodomain associated with Aβ plaques and concomitant changes in its processing enzymes in early stages of AD. Here, we aimed to investigate the effects of recombinant BRI2 ectodomain (rBRI276-266) on Aβ aggregation and on important molecular pathways involved in early stages of AD, including the unfolded protein response (UPR), phosphorylation and truncation of tau, as well as apoptosis. We found that rBRI276-266 delays Aβ fibril formation, although less efficiently than the BRI2 BRICHOS domain (BRI2 residues 113-231). In human neuroblastoma SH-SY5Y cells, rBRI276-266 slightly decreased cell viability and increased up to two-fold the Bax/Bcl-2 ratio and the subsequent activity of caspases 3 and 9, indicating activation of apoptosis. rBRI276-266 upregulated the chaperone BiP but did not modify the mRNA expression of other UPR markers (CHOP and Xbp-1). Strikingly, rBRI276-266 induced the activation of GSK3β but not the phosphorylation of tau. However, exposure to rBRI276-266 significantly induced the truncation of tau, indicating that BRI2 ectodomain can contribute to NFT formation. Since BRI2 can also regulate the metabolism of Aβ, the current data suggests that BRI2 ectodomain is a potential nexus between Aβ, tau pathology and neurodegeneration.