The protein encoded by this gene is a lysosomalcysteine protease composed of a dimer of disulfide-linked heavy and light chains, both produced from a single protein precursor. It is a member of the peptidase C1 family. At least five transcript variants encoding the same protein have been found for this gene.
A wide array of diseases result in elevated levels of cathepsin B, which causes numerous pathological processes including cell death, inflammation, and production of toxic peptides. Focusing on neurological diseases, cathepsin B gene knockout studies in an epileptic rodent model have shown cathepsin B causes a significant amount of the apoptotic cell death that occurs as a result of inducing epilepsy. Cathepsin B inhibitor treatment of rats in which a seizure was induced resulted in improved neurological scores, learning ability and much reduced neuronal cell death and pro-apoptotic cell death peptides. Similarly, cathepsin B gene knockout and cathepsin B inhibitor treatment studies in traumatic brain injury mouse models have shown cathepsin B to be key to causing the resulting neuromuscular dysfunction, memory loss, neuronal cell death and increased production of pro-necrotic and pro-apoptotic cell death peptides. In ischemic non-human primate and rodent models, cathepsin B inhibitor treatment prevented a significant loss of brain neurons, especially in the hippocampus.  In a streptococcus pneumoniae meningitis rodent model, cathepsin B inhibitor treatment greatly improved the clinical course of the infection and reduced brain inflammation and inflammatory Interleukin-1beta (IL1-beta) and tumor necrosis factor-alpha (TNFalpha). In a transgenic Alzheimer's disease (AD) animal model expressing human amyloid precursor protein (APP) containing the wild-type beta-secretase site sequence found in most AD patients or in guinea pigs, which are a natural model of human wild-type APP processing, genetically deleting the cathepsin B gene or chemically inhibiting cathepsin B brain activity resulted in a significant improvement in the memory deficits that develop in such mice and reduces levels of neurotoxic full-length Abeta(1-40/42) and the particularly pernicious pyroglutamate Abeta(3-40/42), which are thought to cause the disease.  In a non-transgenic senescence-accelerated mouse strain, which also has APP containing the wild-type beta-secretase site sequence, treatment with bilobalide, which is an extract of Ginko biloba leaves, also lowered brain Abeta by inhibiting cathepsin B.  Moreover, siRNA silencing or chemically inhibiting cathepsin B in primary rodent hippocampal cells or bovine chromaffin cells, which have human wild-type beta-secretase activity, reduces secretion of Abeta by the regulated secretory pathway. 
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^Hook V, Toneff T, Bogyo M, Greenbaum D, Medzihradszky KF, Neveu J et al. (2005). "Inhibition of cathepsin B reduces β-amyloid production in regulated secretory vesicles of neuronal chromaffin cells: evidence for cathepsin B as a candidate β-secretase of Alzheimer's disease". Biological Chemistry386 (9): 931–940. doi:10.1515/BC.2005.108. PMID16164418.
^Klein DM, Felsenstein KM, Brenneman DE (2009). "Cathepsins B and L differentially regulate amyloid precursor protein processing". J Pharmacol Exp Ther329 (3): 813–21. PMID19064719.
^ abPavlova A, Björk I (September 2003). "Grafting of features of cystatins C or B into the N-terminal region or second binding loop of cystatin A (stefin A) substantially enhances inhibition of cysteine proteinases". Biochemistry42 (38): 11326–33. doi:10.1021/bi030119v. PMID14503883.Vancouver style error (help)
^Estrada S, Nycander M, Hill NJ, Craven CJ, Waltho JP, Björk I (May 1998). "The role of Gly-4 of human cystatin A (stefin A) in the binding of target proteinases. Characterization by kinetic and equilibrium methods of the interactions of cystatin A Gly-4 mutants with papain, cathepsin B, and cathepsin L". Biochemistry37 (20): 7551–60. doi:10.1021/bi980026r. PMID9585570.Vancouver style error (help)
^Mai J, Finley RL, Waisman DM, Sloane BF (April 2000). "Human procathepsin B interacts with the annexin II tetramer on the surface of tumor cells". J. Biol. Chem.275 (17): 12806–12. doi:10.1074/jbc.275.17.12806. PMID10777578.