A gradient of matrix-bound FGF-2 and perlecan is available to lens epithelial cells

Abstract

Fibroblast growth factors play a key role in regulating lens epithelial cell proliferation and differentiation via an anteroposterior gradient that exists between the aqueous and vitreous humours. FGF-2 is the most important for lens epithelial cell proliferation and differentiation. It has been proposed that the presentation of FGF-2 to the lens epithelial cells involves the lens capsule as a source of matrix-bound FGF-2. Here we used immunogold labelling to measure the matrix-bound FGF-2 gradient on the inner surface of the lens capsule in flat-mounted preparations to visualize the FGF-2 available to lens epithelial cells. We also correlated FGF-2 levels with levels of its matrix-binding partner perlecan, a heparan sulphate proteoglycan (HSPG) and found the levels of both to be highest at the lens equator. These also coincided with increased levels of phosphorylated extracellular signal-regulated kinase 1 and 2 (pERK1/2) in lens epithelial cells that localised to condensed chromosomes of epithelial cells that were Ki-67 positive. The gradient of matrix-bound FGF-2 (anterior pole: 3.7 ± 1.3 particles/μm2; equator: 8.2 ± 1.9 particles/μm2; posterior pole: 4 ± 0.9 particles/μm2) and perlecan (anterior pole: 2.1 ± 0.4 particles/μm2; equator: 5 ± 2 particles/μm2; posterior pole: 1.9 ± 0.7 particles/μm2) available at the inner lens capsule surface was measured for the bovine lens. These data support the anteroposterior gradient hypothesis and provide the first measurement of the gradient for an important morphogen and its HSPG partner, perlecan, at the epithelial cell-lens capsule interface.

Regulation of c-Maf and αA-Crystallin in Ocular Lens by Fibroblast Growth Factor Signaling

“…Primary rodent lens cell culture experiments showed that addition of a "high" concentration of bFGF/FGF2 (40 ng/ml) alone induced lens fiber cell terminal differentiation while "low" (0.15 ng/ml) and moderate (3 ng/ml) concentrations control cell survival and migration, respectively (3)(4)(5). FGF signaling is also modulated by the lens capsule, an extracellular matrix serving as an interface between the lens, aqueous and vitreous humor (6,7). Subsequent genetic studies of FGF receptors (8,9), components of the Frs2␣/Ras/MAPK signaling arm (10 -13), and the cooperating heparan sulfate biosynthesis pathway (14,15) demonstrated in vivo roles of FGF signaling in mouse lens fiber cell survival and differentiation, and identified a set of lens regulatory genes, including c-Maf, Prox1, Etv1 (ER81), and Etv5 (ERM), whose expression was attenuated following genetic disruption of the FGF signaling pathway (9,14,15).…”

Fibroblast Growth Factor 2 Protein Stability Provides Decreased Dependence on Heparin for Induction of FGFR Signaling and Alters ERK Signaling Dynamics

“…Because the intensity, duration and gradients of FGF2 signaling are important determinants of developmental outcomes in vivo and cell behavior in vitro (Serls et al, 2005;Roszell et al, 2009;Ameri et al, 2010;Wu et al, 2014), any potential use of FGF2-STABs in established protocols, such as for stem cell culture, directed differentiation of cells, organoid formation, or in tissue engineering requires additional testing to determine optimal FGF2-STAB concentration and treatment duration.…”

β1‐integrin controls cell fate specification in early lens development

“…Low levels of FGF induced ERK phosphorylation induces LEC proliferation (Iyengar et al, 2009) while increased FGF induced ERK phosphorylation drives fiber cell differentiation (Lovicu and McAvoy, 2001), at least in part via upregulation of Maf and Prox1 expression (Audette et al, 2016; Xie et al, 2016; Zhao et al, 2008). 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).…”