Integrin linked kinase (ILK) is required for lens epithelial cell survival, proliferation and differentiation

Abstract

While the role of growth factors in lens development has been investigated extensively, the role of extracellular matrix signalling is less well understood. The developing lens expresses predominantly laminin-binding integrins (such as α3β1, α6β1), which are cooperatively required in the lens epithelium during development. We investigated the role of ILK, a downstream mediator of integrin signalling in mice conditionally null for Ilk. Mutant lenses showed epithelial thinning at E17.5 with reduced proliferation and epithelial cell number and aberrant fibre differentiation. There was complete loss of the central epithelium from postnatal day (P) 2 due to cell death followed by fibre cell degeneration and death by P10 as well as rupture of the lens capsule between P10 and P21. At E17.5 there was significant inhibition (∼50%) of epithelial cell cycle progression, as shown by BrdU incorporation, cyclin D1/D2 and phospho-histone H3 immunostaining. The epithelial marker, E-cadherin, was decreased progressively from E17.5 to P2, in the central epithelium, but there was no significant change in Pax6 expression. Analyses of ERK and Akt phosphorylation indicated marked depression of MAPK and PI3K-Akt signalling, which correlated with decreased phosphorylation of FRS2α and Shp2, indicating altered activation of FGF receptors. At later postnatal stages there was reduced or delayed expression of fibre cell markers (β-crystallin and p57(kip2)). Loss of Ilk also affected deposition of extracellular matrix, with marked retention of collagen IV within differentiating fibre cells. By quantitative RT-PCR array there was significantly decreased expression of 19 genes associated with focal adhesions, actin filament stability and MAPK and PI3K/Akt signalling. Overall, these data indicate that ILK is required for complete activation of signalling cascades downstream of the FGF receptor in lens epithelium and fibre cells during development and thus is involved in epithelial proliferation, survival and subsequent fibre differentiation.

Efficacy of Postnatal In Vivo Nonsense Suppression Therapy in a Pax6 Mouse Model of Aniridia

“…Through the ruptured lens capsule, lens fiber cells were extruded into the vitreous cavity, an uncommon but striking phenomenon observed in several other mouse mutants ( Ilk , Abi2 , Bcar3 ) 28, 29, 30. Although these examples are gene specific and show high levels of penetrance, the rupture of the lens capsule could be a secondary event due to failure of hyaloid vasculature regression 23 .…”

Nonlinear ionizing radiation-induced changes in eye lens cell proliferation, cyclin D1 expression and lens shape

“…Interestingly, RAD51 is thought to bind cyclin D1, which can also participate in the repair of DSBs [ 38 , 39 ]. In the lens, cyclin D1 levels correlate with cell proliferation in the GZ at the lens periphery [ 11 , 40 ]. This zone is also believed to be most sensitive to IR damage [ 12 , 13 ].…”

β1‐integrin controls cell fate specification in early lens development

“…In contrast, all lens cells of E12.5 β1LE lenses (Figure 7D – arrowheads) strongly stain for pAKT, including the cells of the posterior lens exhibiting the morphological characteristics of lens fibers. We next tested whether these elevations in pERK and pAKT could be mediated by FGF receptor (FGFR) signaling by staining lenses for pFRS2α, a downstream effector of FGF signaling (Li et al, 2014; Madakashira et al, 2012; Teo et al, 2014). At E13.5, control lenses exhibited pFRS2α staining throughout the lens epithelium into the transition zone (Figure 7E), while β1LE lenses exhibited intense pFRS2α staining in the cells of the anterior lens at this stage (Figure 7F, arrowheads).…”

“…In the eye, the selective differentiation of lens fiber cells at the lens equator has been attributed to a gradient of FGF that is produced in the posterior compartment of the eye (Wu et al, 2014). However, the entire anterior lens epithelium of the early lens exhibits FGF signaling as measured by phosphorylation of the FGF receptor effector, FRS2α, (Madakashira et al, 2012; Teo et al, 2014) (see Figure 7). Overall, the mechanisms that fine-tune the differential response of the anterior and posterior lens vesicle to FGF in vivo are less well understood…”