Probes for INS

ADAMTS18 is an orphan member of the ADAMTS family of metalloproteinase. ADAMTS18 mutation has been linked to developmental eye disorders, such as retinal dystrophies and ectopia lentis. Here, we report a new function of ADAMTS18 in modulating the lacrimal gland (LG) branching morphogenesis, and an association with dry eye in mice. Adamts18 mRNA was found to be enriched in the epithelium of branching tips of embryonic (E) LG, but its expression was barely detectable after 2 weeks of birth. Histological analyses of E16.5-E17.5 LG showed that ADAMTS18 deficiency resulted in a significant reduction of epithelial branching in embryonic LG. In vitro culture of E15.5 LG explants showed that the numbers of epithelial buds and branches in Adamts18 knockout (Adamts18-/-) LGs were significantly decreased when compared to those of wild type (Adamts18+/+) LGs after 0 h, 24 h, and 48 h of culture. Increased fibronectin deposition was detected in LG mesenchyme of E16.5 Adamts18-/- mice. At 14 months of age, Adamts18-/- mice manifested multiple LG pathological changes, including acinar atrophy and irregular duct ectasis with periductal fibrosis. The tear volume was significantly decreased in Adamts18-/- mice at 4 months of age, which corresponds to early adulthood in humans.

The ADAMTS (A Disintegrin and Metalloproteinase with Thrombospondin Motifs) enzymes are secreted metalloproteinases with major roles in development, morphogenesis, and tissue repair via the assembly and degradation of extracellular matrix (ECM). In this study, we investigated the role of ADAMTS18 in the development of the reproductive tract in female mice by phenotyping Adamts18 knockout (Adamts18-/-) mice. The results showed that Adamst18 mRNAs were abundantly expressed in vaginal epithelial cells and muscularis cells of the developing vagina. At the time of vaginal opening (5 weeks of age), about 41 % of Adamts18-/- females showed enlarged protrusions in the upper and middle parts of the vagina, reduced vaginal length, and simultaneously exhibited vaginal atresia. 6% Adamts18-/- females exhibited vaginal septum. Histological analyses revealed that the paired Mullerian ducts in ∼33 % female Adamts18-/- embryos failed to fuse at embryonic day 15.5 (E15.5) resulting in the formation of two vaginal cavities. Results of TUNEL assay and immunohistochemistry for caspase-3 showed that the number of apoptotic cells in the terminal portion of the vagina of 5-week-old Adamts18-/- females with vaginal atresia was significantly decreased. Adamts18-/- females also showed a significant decrease in serum estradiol E2 compared to age-matched Adamts18+/+ females. Results of qRT-PCR showed that the expression level of the anti-apoptosis gene Bcl-2 was significantly increased and that of the apoptosis-related gene Epha1 was decreased in the vagina of 5-week-old Adamts18-/- females. These results suggest that ADAMTS18 regulates vaginal opening through influencing the fusion of Mullerian ducts and apoptosis of vaginal cells in mice.

ADAMTS18 was identified in 2002 as a member of the ADAMTS family of 19 secreted Zinc-dependent metalloproteinases. Prior to 2016, ADAMTS18 was known as a candidate gene associated with a wide range of pathologies, particularly various malignancies and eye disorders. However, functions and substrates of ADAMTS18 in normal conditions were unknown. Since 2016, with the development of Adamts18 knockout models, many studies had been conducted on the Adamts18 gene in vivo. These studies revealed that ADAMTS18 is essential for the morphology and organogenesis of several epithelial organs (e.g., lung, kidney, breast, salivary glands, and lacrimal glands), vascular and neuronal systems, adipose tissue, and reproductive tracts. In this review, we describe the current understanding of ADAMTS18 and its substrates and regulators. Limitations in translating new findings on ADAMTS18 to clinical practice are also discussed.

Members of the ADAMTS family have been implicated in various vascular diseases. However, their functional roles in early embryonic vascular development are unknown. In this study, we showed that Adamts18 is highly expressed at E11.5-E14.5 in cells surrounding the embryonic aortic arch (AOAR) and the common carotid artery (CCA) during branchial arch artery development in mice. Adamts18 deficiency was found to cause abnormal development of AOAR, CCA, and the 3rd and 4th branchial arch appendages, leading to hypoplastic carotid body, thymus, and variation of middle cerebral artery. Adamts18 was shown to affect the accumulation of extracellular matrix (ECM) components, in particular fibronectin (Fn), around AOAR and CCA. As a result of increased Fn accumulation, the Notch3 signaling pathway was activated to promote the differentiation of cranial neural crest cells (CNCCs) to vascular smooth muscle cells. These data indicate that Adamts18-mediated ECM homeostasis is crucial for the differentiation of CNCCs.