UV-induced LESC damage causing pterygium is prevalent in sunny and dry climates, but also affects patients in Northern Europe (1-10%). It is estimated that an expected 10% of all refugees who came to Germany from southern countries are suffering from pterygium (i.e.>100.000), making new treatments more imperative. Understanding the mechanisms by which autophagy changes contribute to pterygium pathogenesis will lead to new therapies to limit recurrence, a major problem after pterygium surgery.

Vision is a key sensory function. The transparent and avascular cornea (“windscreen of the eye”) is essential for sight. It’s primary refractive layer, the corneal epithelium, is maintained via ABCB5-expressing limbal epithelial stem cells (LESC) located at the junction between the avascular cornea and the densely (lymph)vascularized conjunctiva.
Due to their position, LESC are exposed to UV irradiation, which can damage their niche and function. Increased levels of autophagic activity within the basal limbal epithelium indicate that LESCs employ autophagy to repair damage accumulating during their long cycle. Pterygium, a tumour of the conjunctiva which grows onto the cornea impairing vision is linked to UV-induced LESC damage. We have previously reported that LESCs differentiate under UV exposure, leading to a pro-inflammatory shift in their niche. Pterygium is linked to reduced autophagy via mTORC1in the epithelium which boosts proliferation and causes aberrant apoptosis. The direct involvement of the LESCS in pterygium pathogenesis via this mechanism is unclear.
Therefore, we aim to:

1. elucidate the molecular mechanisms by which autophagy affects the maintenance of ABCB5-positive LESCs phenotype and how these change in pterygium and
2. unravel if and how UV light damages ABCB5-positive LESCs via reduction of autophagic activity.

A better understanding of the autophagic activity mechanisms exerted by LESC and their damage by UV light will open the way to new treatment options in the form of mTOR inhibitors against UV-related stem cell disorders in the eye and beyond.

1. Assessment of the role of autophagy in UVB-response in pterygium, limbus and conjunctiva.

• In situ assessment of autophagy –related proteins and putative stem cell marker distribution in primary and recurrent pterygium, limbus and conjunctiva.
• Assessment of autophagy induction in the limbal stem cell compartment following UVB irradiation by UVB irradiation of human pterygium, limbal and conjunctiva ABCB5-positive stem cells.
• Evaluation of the function of autophagy following UVB irradiation of human pterygium, limbal and conjunctiva.
• Paracrine effect of autophagy deficient-sufficient UVB treated/non-treated ABCB5 positive and negative cells from pterygium, limbus and conjunctiva 2. Use of in vivo models to evaluate the role of autophagy following UVB irradiation (collaboration with Prof. Björn Schumacher)

2. Assessment of the autophagy response to UV-irradiation of an ABCB5-KO model

• We will study the response of the autophagy-defficent mice to UVB treatment in terms of assessment of lymphangiogenesis as well as assessment of immune cell infiltration

Our group has recently used an in vitro approach to study the effect of UVA and UVB on the phenotype and functionality of human limbal epithelial cells and their accessory limbal fibroblasts, as well as on their paracrine signalling activities associated with the regulation of inflammation and (lymph)angiogenesis^1,2. Our findings suggested that this short-term UV irradiation induced the loss of the stem-like character of limbal epithelial cells (Figure 1). Interestingly, limbal epithelial cells co-cultured with UV-irradiated limbal fibroblasts also exhibited loss of SC character and decrease of colony-forming efficiency^1,2.

Following UVB treatment, pro-angiogenic factors were down regulated while pro-inflammatory and macrophage-recruiting cytokines such as TNF-α, IFNγ and MCP1 were significantly upregulated (Figure 2).

This demonstrates that by producing these cytokines, both HLE and HLF cells may contribute to the inflammatory mechanisms taking place in the cornea following UVB irradiation. In addition, we have recently demonstrated that UV blocking contact prevented these UVB-induced adverse effects as well as DNA damage. These data demonstrated the significance of UV-protection in preserving the limbal niche in response to UVB irradiation, suggesting that protecting the niche, especially after LESC transplantation and in patients after pterygium surgery, may prevent recurrences³.Taken together, these observations demonstrate that UV irradiation dysregulates limbal niche cells while inducing a pro-inflammatory environment which promotes neovascularisation.
Although UV-induced changes in the limbal niche have already been described, the exact mechanisms through which these occur remain unidentified. Recent preliminary studies have shown that autophagy regulates cell cycle response in limbal epithelial cultures under UVA stress and that autophagy-deficient cells are not able to restore reactive oxygen species accumulation mediated by the nuclear to cytoplasm translocation of pax6; however, the events following UVB treatment as well as the specific effects on the stem cell population have not been investigated. This project will aim to address these questions.