In vivo and in vitro studies to identify the biological function of peptides derived from the NGF precursor processing, and their role in the regulation of NGF receptors expression

Nerve growth factor (NGF), a well-explored neurotrophin primarily associated with neurons, has recently been discovered to have functional roles beyond the central nervous system (CNS) and peripheral nervous system (PNS), when working in conjunction with its precursor. The equilibrium between NGF and its precursor, proNGF, and their corresponding receptors, predominantly TrkA and P75NTR, plays a critical role in maintaining cellular, tissue, and organ homeostasis. Furthermore, this equilibrium has been recognized as an indicator of pathological conditions, including neurodegeneration, tissue damages and cancer. During the maturation process of proNGF, it undergoes enzymatic cleavage by proteases, leading to the production of mature NGF, while simultaneously releasing various fragments and peptides, including the prodomain fragments (pdNGF), the functions of which remain less understood. This research project aimed to investigate the biological functions of these proNGF fragments and their influence on the regulation of NGF receptors. In vivo studies were conducted to examine the processing of proNGF in the tissues of adult rats under normal physiological conditions and in response to inflammation induced by intraperitoneal injection of Lipopolysaccharide (LPS). It was observed that the processing of proNGF was tissue-specific, and an accumulation of prodomain fragments occurred following inflammation, indicating a potential correlation between organ function and the response to insults. Notably, in testis tissue, the increased levels of pdNGF were associated with heightened expression of p75NTR ICD, a decrease in the glycosylated form of TrkA, and an increase in the phosphorylated form of TrkA, around 100kDa. These findings suggest that the prodomain may bind to different forms of NGF receptors (NGFR) to mediate their functions. Additionally, in vitro studies were conducted to further assess the functions of these peptides. A pool of prodomain peptides, particularly those containing residues between 1-66, as distinct from those containing residues between 70-110, triggered a proapoptotic cascade in primary neurons. Synthetic prodomain peptides were also shown to induce the migration of MCF-7 breast cancer cells. This research contributes to our understanding of the multifaceted roles of proNGF fragments in the regulation of NGF receptors and their implications in various physiological and pathological conditions.