Thrombospondin-1 Is Necessary for the Development and Repair of Corneal Nerves

Abstract

Thrombospondin-1-deficient (TSP-1−/−) mice are used as an animal model of Sjögren’s Syndrome because they exhibit many of the symptoms associated with the autoimmune type of dry eye found in primary Sjögren’s Syndrome. This type of dry eye is linked to the inflammation of the lacrimal gland, conjunctiva, and cornea, and is thought to involve dysfunction of the complex neuronal reflex arc that mediates tear production in response to noxious stimuli on the ocular surface. This study characterizes the structural and functional changes to the corneal nerves that are the afferent arm of this arc in young and older TSP-1−/− and wild type (WT) mice. The structure and subtype of nerves were characterized by immunohistochemistry, in vivo confocal microscopy, and confocal microscopy. Cytokine expression analysis was determined by Q-PCR and the number of monocytes was measured by immunohistochemistry. We found that only the pro-inflammatory cytokine MIP-2 increased in young corneas of TSP-1−/− compared to WT mice, but tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein-1 (MCP-1), and macrophage inflammatory protein-2 (MIP-2) all increased in older TSP-1−/− mouse corneas. In contrast, CD11b+ pro-inflammatory monocytes did not increase even in older mouse corneas. Calcitonin gene-related peptide (CGRP)-, but not Substance P (SubP)-containing corneal nerves decreased in older, but not younger TSP-1−/− compared to WT mouse corneas. We conclude that CGRP-containing corneal sensory nerves exhibit distinct structural deficiencies as disease progresses in TSP-1−/− mice, suggesting that: (1) TSP-1 is needed for the development or repair of these nerves and (2) impaired afferent corneal nerve structure and hence function may contribute to ocular surface dysfunction that develops as TSP-1−/− mice age.

Topical Application of TGF-β-Activating Peptide, KRFK, Prevents Inflammatory Manifestations in the TSP-1-Deficient Mouse Model of Chronic Ocular Inflammation

“…Well-established signs of ocular surface inflammation are evident at twelve weeks of age. These include the disruption of corneal epithelial barrier integrity, reduced tear mucin levels, and the expression of inflammatory cytokines in cornea, conjunctiva, and lacrimal gland tissues [6,16,17,18,19]. When considering the ability of KRFK to alter the induction of the systemic immune response, here we evaluate its ability to prevent disease progression in TSP-1-deficient mice in a proof-of-concept study.…”

“…Spontaneously developed chronic ocular surface inflammation in TSP-1-deficient mice progresses with age [6,16,18]. While normal at birth, these mice gradually develop chronic ocular surface inflammation, which is fully established by twelve weeks of age with quantifiable clinical signs, like the disrupted corneal epithelial barrier integrity and the secretory dysfunction of mucin secreting conjunctival goblet cells.…”

Mouse Models of Sjögren’s Syndrome with Ocular Surface Disease

“…While CGRP is reported to mediate an anti-inflammatory pathway [45,46], Substance P is known to induce and mediate inflammation [47]. In TSP-1−/− mice, a significant decline in corneal nerves containing CGRP, but not Substance P, is consistent with the presence of inflammation [43]. These observations strongly implicate the contribution of inflammation-mediated impairment of corneal nerves to the loss of LG secretory function noted in TSP-1−/− mice.…”

“…(a) Abnormalities of corneal nerves: neural abnormalities are reported in the corneas of patients with SS and neuropathic corneal mechanical hypersensitivity in SS appears to be induced by ocular surface inflammation [41,42]. Although corneal sensory nerve density is lower in TSP-1−/− mice compared to WT mice, there is no change in the nerve density corresponding with the expression of inflammatory factors in the tissue [43]. Altered morphology of corneal nerves in TSP-1−/− mice, however, is concomitant with an increased expression of the pro-inflammatory cytokines MCP-1, TNFα, and MIP2.…”

Mechanisms of Disease in Sjögren Syndrome—New Developments and Directions

“…Tatematsu et al investigate the structure of corneal nerves, specifically neurotransmitter containing nerves in female Thrombospondin 1 −/− mice of two different ages (4-7 and 9-12 weeks) [23]. Compared to age-matched wild-type mice, Thrombospondin 1 −/− mice had a lower number of corneal nerves both by immunofluorescence in wholemount specimens and in vivo confocal microscopy, which worsened by 12 weeks.…”