Human serum albumin fusion protein as therapeutics for targeting amyloid beta in Alzheimer's diseases

Alzheimer's disease (AD) is characterized by amyloid beta (Aβ) plaques and neurofibrillary tangles. AD drug development has been limited due to the presence of the blood-brain barrier (BBB), which prevents efficient uptake of therapeutics into the brain. To solve this problem, we used trans-activator of transcription (TAT)-transducing domain and added the human serum albumin (HSA) carrier to increase the half-life of the drug within the body. In addition, we included the protein of interest for lowering Aβ deposition and/or neurofibrillary tangles. We made HSA fusion protein (designated AL04) which contains Cystatin C (CysC) as core mechanism of action moiety in the construct containing tandem repeat TAT (dTAT). After purification of 80KDa AL04, we investigate the therapeutic potential of AL04 in vitro and AD mouse model Tg2576. We evaluated the permeability of AL04 through the BBB using a cell-basedhuman BBB model and show that dTAT plays a role in facilitating the delivery of 80 kDa protein. We found out that AL04 attenuates Aβ-induced neurotoxicity in PC12 cells. In Tg2576 mice brain, Aβ plaques were dramatically reduced in AL04 treated mice. These data suggest that BBB-crossing albumin fusion protein AL04 with CysC active moiety can be a disease modifying treatment for AD.

Cystatin C uptake in the eye

BACKGROUND

As a secreted protein, cystatin C is assumed to play its role in the extracellular compartment, where it can inhibit virtually all cysteine proteases of families C1 (cathepsin B, L, S) and C13 (mammalian legumain-related proteases). Since many of its potential target enzymes in the eye reside in intracellular compartments, we sought evidence for a cellular uptake of the inhibitor in ocular tissues.

METHODS

Fluorescence-labeled human cystatin C was injected intravitreally into normal rat eyes. Ocular tissues were subsequently examined using ELISA, fluorescence microscopy, and immunohistochemistry. Cystatin C uptake was additionally studied in an in vitro retina model.

RESULTS

Cystatin C administered intravitreally in vivo is taken up into cells of the corneal endothelium and epithelium, the epithelial cells lining the ciliary processes, and into cells in the neuroretina (mostly ganglion cells) and the retinal pigment epithelium. The uptake is demonstrable also in vitro and was, in the neuroretina, found to be a high-affinity system, inhibited by cooling the specimens or by adding the microfilament polymerization inhibitor, cytochalasin D, to the medium.

CONCLUSIONS

There is an active, temperature-dependent uptake system for cystatin C into several cell types in the cornea, ciliary body, and retina. The cell types that take up cystatin C are generally the same that contain endogenous cystatin C, suggesting that much or all cystatin C seen intracellularly in the normal eye may have been taken up from the surrounding extracellular space. The uptake indicates that the inhibitor may exert biological functions in intracellular compartments. It is also possible that this uptake system may regulate the extracellular levels of cystatin C in the eye.