p75NTR antagonist THX-B increases mature nerve growth factor secretion by bladder cells through decreased activity of matrix metalloproteinase-9

Abstract

In urine samples from an aging female cohort with overactive bladder syndrome (OAB), the proteolytic activity of matrix metalloproteinase-9 (MMP-9), an enzyme which degrades mature NGF, was elevated and associated with low levels of nerve growth factor (NGF). Given that a substantial portion of urine constituents originate from bladder cellular processes, we examined the synthesis of NGF and MMP-9 in rat urothelial (UROs) and smooth muscle (SMCs) cells in culture. NGF and proNGF were found expressed and released by both cell types while UROs were the major source of secreted MMP-9. THX-B, a highly specific p75^NTR antagonist, decreased the expression of MMP-9 resulting in increased mature NGF levels in culture medium of UROs while displaying minor effects on SMCs. Likewise, CRISPR-cas9 genomic deletion of MMP-9 potently increased mature NGF levels in both cell types. On the other hand, THX-B decreased the synthesis and release of α2 Macroglobulin (α2M), a protein that stabilizes proNGF in UROs but increased it in SMCs. THX-B also increased the activity of enzymes furin and matrix metalloproteinase-7 (MMP-7), that convert proNGF to mature NGF in UROs, yielding a net increase in mature NGF and a decrease of proNGF. We conclude that p75^NTR is involved in the control of proNGF and mature NGF secretion from bladder cells through modulation of proteolytic activities. Since neurotrophins and binding to their receptors are relevant to pathologies, inhibition of p75^NTR by THX-B may be exploited in a therapeutic strategy.