Biglycan and related therapeutics and methods of use
The invention provides compositions and methods for treating, preventing, and diagnosing diseases or conditions associated with an abnormal level or activity of biglycan; disorders associated with an unstable cytoplasmic membrane, due, e.g., to an unstable dystrophin associated protein complex (DAPC); disorders associated with abnormal synapses or neuromuscular junctions, including those resulting from an abnormal MuSK activation or acetylcholine receptor (AChR) aggregation. Example of diseases include muscular dystrophies, such as Duchenne's Muscular Dystrophy, Becker's Muscular Dystrophy, neuromuscular disorders and neurological disorders.
1. A method for activating the cell-surface receptor muscle, skeletal, receptor tyrosine kinase (MuSK) in a cell having an abnormal dystrophin-associated protein complex (DAPC), comprising contacting the cell with a biglycan therapeutic in an amount effective to potentiate agrin-induced phosphorylation of the receptor MuSK, wherein the abnormal DAPC is caused by one or more of (i) a mutation in a DAPC component, or (ii) an abnormally lower level of a DAPC component compared to a control cell, wherein the DAPC component is: a dystroglycan, dystrophin, or a sarcoglycan, and wherein the receptor MuSK is activated thereby.
2. The method of claim 1 , wherein the biglycan therapeutic upregulates utrophin levels.
3. The method of claim 1 , wherein the biglycan therapeutic is a polypeptide including a biglycan amino acid sequence which is at least about 90% identical to SEQ ID NO: 9.
4. The method of claim 3 , wherein the biglycan amino acid sequence includes one or more Leucine Rich Repeats (LRRs) of human biglycan having SEQ ID NO: 9.
5. The method of claim 3 , wherein the polypeptide is derivatized with one or more glycosaminoglycan (GAG) side chains.
6. The method of claim 1 , wherein the biglycan amino acid sequence is at least about 90% identical to amino acids 38-365 of SEQ ID NO: 9.
7. The method of claim 6 , wherein the biglycan amino acid sequence is at least about 95% identical to amino acids 38-365 of SEQ ID NO: 9.
8. The method of claim 3 , wherein the cell is a muscle cell.
9. The method of claim 1 further comprising assaying activity of the receptor MuSK, wherein the assay for the receptor MuSK activity comprises determining the phosphorylation state of the receptor MuSK.
10. The method of claim 1 , wherein the biglycan therapeutic binds to alpha-sarcoglycan and gamma-sarcoglycan.
11. The method of claim 1 , wherein the biglycan therapeutic stimulates phosphorylation of alpha-sarcoglycan on a cell membrane.
12. The method of claim 3 , wherein the biglycan amino acid sequence is identical to amino acids 38-365 of SEQ ID NO: 9.
13. The method of claim 3 , wherein the biglycan amino acid sequence is encoded by a nucleic acid which hybridizes under stringent conditions of 6.0×sodium chloride/sodium citrate (SSC) at about 45° C. to a complementary strand of SEQ ID NO: 8.