Nerve Growth Factor Regulates Neurolymphatic Remodeling during Corneal Inflammation and Resolution

Abstract

The cellular and physiologic mechanisms that regulate the resolution of inflammation remain poorly defined despite their widespread importance in improving inflammatory disease outcomes. We studied the resolution of two cardinal signs of inflammation–pain and swelling–by investigating molecular mechanisms that regulate neural and lymphatic vessel remodeling during the resolution of corneal inflammation. A mouse model of corneal inflammation and wound recovery was developed to study this process in vivo. Administration of nerve growth factor (NGF) increased pain sensation and inhibited neural remodeling and lymphatic vessel regression processes during wound recovery. A complementary in vivo approach, the corneal micropocket assay, revealed that NGF-laden pellets stimulated lymphangiogenesis and increased protein levels of VEGF-C. Adult human dermal lymphatic endothelial cells did not express canonical NGF receptors TrkA and p75NTR or activate downstream MAPK- or Akt-pathway effectors in the presence of NGF, although NGF treatment increased their migratory and tubulogenesis capacities in vitro. Blockade of the VEGF-R2/R3 signaling pathway ablated NGF-mediated lymphangiogenesis in vivo. These findings suggest a hierarchical relationship with NGF functioning upstream of the VEGF family members, particularly VEGF-C, to stimulate lymphangiogenesis. Taken together, these studies show that NGF stimulates lymphangiogenesis and that NGF may act as a pathogenic factor that negatively regulates the normal neural and lymphatic vascular remodeling events that accompany wound recovery.

The lymphatic system and pancreatic cancer

“…Such mediators include growth factors fibroblast growth factor-2 (FGF-2) [129], platelet-derived growth factor-BB (PDGF-BB) [130,131], nerve growth factor (NGF) [132], insulin-like growth factor-1 (IGF-1) and -2 [133], and hepatocyte growth factor (HGF) [134]; inflammatory cytokines interleukin-1 β (IL-1β) [135,136] and tumor necrosis factor- α (TNF-α) [135–137]; and other non-traditional signaling molecules lipid sphingosine-1-phosphate [138], cyclooxygenase 2 (Cox2), and EP3/4 [139]. A role for integrins in lymphangiogenesis is also emerging with evidence of binding of VEGF-A, -C, and -D to lymphatic endothelial-specific integrin-α9β1 [140,141].…”

“…This likely occurs through activation of the NFκB promoter to induce VEGF-C expression [137]. Other indirect inducers of lymphangiogenesis include Cox2 and EP3/4, which may increase expression of VEGF-C and -D to modulate cell growth during inflammation [139], and NGF, which increased expression of VEGF-C, but not VEGF-A, in a mouse corneal model of lymphangiogenesis [132]. Some studies have attributed the secondary production of VEGFs, specifically VEGF-C, to an infiltrating macrophage population during periods of inflammation and malignancy [135,138,143,144].…”

“…Studies have shown that lymphatic vessels are, in fact, innervated [289,290] and have suggested that these connections may represent an additional route of metastatic dissemination of tumor cells from either network to the other [77,291]. It is well documented that vasculature and nerves can respond to the same molecular cues—termed neurovascular guidance molecules—for development and remodeling [132,168–170,292,293], and many of these molecules, such as Nrp-1 and -2, NGF, brain-derived neurotrophic factor (BDNF), FGF, IGF-2, Netrin-1, Semaphorin-3A, Ephrin receptor B4, Slit2, and Robo1 may be differentially expressed or have altered signaling functions in the pancreatic tumor microenvironment, implicating them in cancer progression [171,172,294–300]. As well, somatic alterations in axon guidance pathway genes are observed in a subset of pancreatic cancer genomes [301].…”

“…Corneal injury can be recapitulated experimentally by placement of sutures, mechanical debridement, or chemical burn. A refinement of this inflammatory model enabling more mechanistic dissection of lymphatic vessel behavior is the corneal micropocket assay in which a micropellet can be loaded with a protein or drug of interest and implanted into the cornea [132,308,309]. Further modifications of traditional acute inflammatory protocols can induce wound recovery [132,310] and recurrent inflammation [132,311]—two additional distinct physiological microenvironments with implications for wound healing, chronic inflammatory disease, and tumor microenvironment research.…”

Advances in Biomedical Imaging, Bioengineering, and Related Technologies for the Development of Biomarkers of Pancreatic Disease

“…As one example, CDK5, a kinase with homology to cyclin dependent kinases, but with distinct functions that include contributions to neural tissue patterning and nociception, is overexpressed and hyperactivated in a high percentage of human pancreatic cancers, especially in areas of perinerual invasion 39 . The concept that pancreatic cancers undertake tissue remodeling including perineural invasion during progression led to investigations of the influence of inflammation and tumor growth on neurolymphatic remodeling 40 , nociception, and other pain related processes.…”