ABCB5+ Limbal Epithelial Stem Cells Inhibit Developmental but Promote Inflammatory (Lymph) Angiogenesis While Preventing Corneal Inflammation.

The limbus, the vascularized junction between the cornea and conjunctiva, is thought to function as a barrier against corneal neovascularization. However, the exact mechanisms regulating this remain unknown. In this study, the limbal epithelial stem cell (LESC) marker ABCB5 was used to investigate the role of LESCs in corneal neovascularization. In an ABCB5KO model, a mild but significant increase of limbal lymphatic and blood vascular network complexity was observed in developing mice (4 weeks) but not in adult mice. Conversely, when using a cornea suture model, the WT animals exhibited a mild but significant increase in the number of lymphatic vessel sprouts compared to the ABCB5KO, suggesting a contextual anti-lymphangiogenic effect of ABCB5 on the limbal vasculature during development, but a pro-lymphangiogenic effect under inflammatory challenge in adulthood. In addition, conditioned media from ABCB5-positive cultured human limbal epithelial cells (ABCB5+) stimulated human blood and lymphatic endothelial cell proliferation and migration. Finally, a proteomic analysis demonstrated ABCB5+ cells have a pro(lymph)angiogenic as well as an anti-inflammatory profile. These data suggest a novel dual, context-dependent role of ABCB5+ LESCs, inhibiting developmental but promoting inflammatory (lymph)angiogenesis in adulthood and exerting anti-inflammatory effects. These findings are of high clinical relevance in relation to LESC therapy against blindness.

Short-Term UVB Irradiation Leads to Persistent DNA Damage in Limbal Epithelial Stem Cells, Partially Reversed by DNA Repairing Enzymes.

The cornea is frequently exposed to ultraviolet (UV) radiation and absorbs a portion of this radiation. UVB in particular is absorbed by the cornea and will principally damage the topmost layer of the cornea, the epithelium. Epidemiological research shows that the UV damage of DNA is a contributing factor to corneal diseases such as pterygium. There are two main DNA photolesions of UV: cyclobutane pyrimidine dimers (CPDs) and pyrimidine-pyrimidone (6-4) photoproducts (6-4PPs). Both involve the abnormal linking of adjacent pyrimide bases. In particular, CPD lesions, which account for the vast majority of UV-induced lesions, are inefficiently repaired by nucleotide excision repair (NER) and are thus mutagenic and linked to cancer development in humans. Here, we apply two exogenous enzymes: CPD photolyase (CPDPL) and T4 endonuclease V (T4N5). The efficacy of these enzymes was assayed by the proteomic and immunofluorescence measurements of UVB-induced CPDs before and after treatment. The results showed that CPDs can be rapidly repaired by T4N5 in cell cultures. The usage of CPDPL and T4N5 in ex vivo eyes revealed that CPD lesions persist in the corneal limbus. The proteomic analysis of the T4N5-treated cells shows increases in the components of the angiogenic and inflammatory systems. We conclude that T4N5 and CPDPL show great promise in the treatment of CPD lesions, but the complete clearance of CPDs from the limbus remains a challenge.

Egr1 loss-of-function promotes beige adipocyte differentiation and activation specifically in inguinal subcutaneous white adipose tissue.

In mice, exercise, cold exposure and fasting lead to the differentiation of inducible-brown adipocytes, called beige adipocytes, within white adipose tissue and have beneficial effects on fat burning and metabolism, through heat production. This browning process is associated with an increased expression of the key thermogenic mitochondrial uncoupling protein 1, Ucp1. Egr1 transcription factor has been described as a regulator of white and beige differentiation programs, and Egr1 depletion is associated with a spontaneous increase of subcutaneous white adipose tissue browning, in absence of external stimulation. Here, we demonstrate that Egr1 mutant mice exhibit a restrained Ucp1 expression specifically increased in subcutaneous fat, resulting in a metabolic shift to a more brown-like, oxidative metabolism, which was not observed in other fat depots. In addition, Egr1 is necessary and sufficient to promote white and alter beige adipocyte differentiation of mouse stem cells. These results suggest that modulation of Egr1 expression could represent a promising therapeutic strategy to increase energy expenditure and to restrain obesity-associated metabolic disorders.