Michael E. Stern

Effect of TGF-β on ocular surface epithelial cells.

A role for transforming growth factor (TGF)-β in the pathogenesis of some ocular surface diseases has been proposed. We determined if secretion of TGF-β and expression of TGF-β receptors RI, RII, and RIII by human ocular surface epithelial cells were modified under inflammatory conditions. We also determined how these cells responded to TGF-β. A human corneal epithelial (HCE) cell line and a conjunctival epithelial cell line (IOBA-NHC) were exposed to TGF-β1 and -β2 and to proinflammatory cytokines. TGF-β receptor mRNAs were analyzed by real time reverse transcription polymerase chain reaction (RT-PCR) in both cell lines, and in conjunctival, limbal, and corneal epithelial cells from post-mortem human specimens. Expression of TGF-β receptors and pSMAD2/SMAD2 were determined by Western blot and immunofluorescence assays. Secretion of TGF-β isoforms, cytokine/chemokine, and metalloproteinases (MMPs) were analyzed in cell supernatants by immunobead-based assays. Secretory leukocyte proteinase inhibitor (SLPI) secretion was analyzed by enzyme-linked immunosorbent assay. TGF-β isoform and receptor gene expression was determined by RT-PCR in conjunctival epithelium of dry eye (DE) patients and healthy subjects. Our results showed that TGF-β RI expression was down-regulated with IL-4 exposure, whereas TGF-β RII and TGF-β2 were upregulated by TNF-α in HCE cells. TGF-β RIII receptor expression was upregulated in IOBA-NHC cells by TNF-α and IFN-γ. SMAD2 phosphorylation occurred in HCE and IOBA-NHC cells after TGF-β treatment. TGF-β significantly up- and down-regulated secretion of several cytokines/chemokines by both cell lines and MMP by HCE cells. TGF-β2 and TGF-β3 were upregulated and TGF-β RIII mRNA was down-regulated in DE conjunctival epithelium. These results show that TGF-β plays an important role in directing local inflammatory responses in ocular surface epithelial cells.

Pathogenesis: Emphasis on Dry Eye and the Role of the Lacrimal Functional Unit in Sjögren’s Syndrome

Sjogren’s syndrome lacrimal keratoconjunctivitis is a chronic autoimmune disease that has a significant impact on the quality of patient’s lives throughout the world. Current evidence suggests that dysfunction of the complex lacrimal function unit (LFU: cornea, conjunctiva, lacrimal glands, and meibomian glands) results in unstable tear film and chronic inflammation. Inflammatory cell (e.g., CD4+ T cells) infiltration, elevated pro-inflammatory cytokine levels, increased epithelial cell apoptosis, and diminished goblet cell numbers within the LFU, coupled with decreased tear production, are hallmark features of Sjogren’s syndrome. The inability of lacrimal glands to adequately respond to signals of ocular surface dryness, an early feature of Sjogren’s syndrome, is hypothesized to perpetuate chronic inflammation. The cycle of autoimmunity during Sjogren’s syndrome is simplified into two main stages: (1) the afferent arm, in which desiccating stress on the ocular surface elicits the initial immune response and (2) an efferent arm, which describes activation and homing of autoreactive CD4+ T cells to the ocular surface that contribute to local tissue remodeling and destruction. Indeed, early inflammatory intervention can restore secretory function within the LFU; however, if left untreated, chronic inflammation may irreversibly impact the function of the lacrimal glands and/or conjunctival goblet cells. Current research is focused on gaining a better understanding of the mechanisms that contribute to the immunopathogenesis of Sjogren’s syndrome with the goals of developing sensitive diagnostics and superior therapeutics.