TGFβ-Smad signalling in postoperative human lens epithelial cells

S Saika

T Miyamoto

I Ishida

K Shirai

Y Ohnishi

A Ooshima

J McAvoy

^{Department of Ophthalmology, Wakayama Medical University, Wakayama, Japan}

^{Department of Pathology, Wakayama Medical University, Wakayama, Japan}

^{Save Sight Institute and Department of Anatomy and Histology, University of Sydney, Sydney, NSW, Australia}

Correspondence to:
Shizuya Saika, MD, PhD, Department of Ophthalmology, Wakayama Medical University, 811-1 Kimiidera, Wakayama, 641-0012, Japan;
pj.ca.dem-amayakaw@ayuzihs

Accepted 2002 Jul 17.

Abstract

Aims: To localise Smads3/4 proteins in lens epithelial cells (LECs) of fresh and postoperative human specimens. Smads3/4 are involved in signal transduction between transforming growth factor β (TGFβ) cell surface receptors and gene promoters. Nuclear localisation of Smads indicates achievement of endogenous TGFβ signalling in cells.

Methods: Three circular sections of the anterior capsule, one lens, and 17 capsules undergoing postoperative healing were studied. Immunohistochemistry was performed for Smads3/4 in paraffin sections of the specimens. The effect of exogenous TGFβ2 on Smad3 subcellular localisation was examined in explant cultures of extracted human anterior lens epithelium.

Results: The cytoplasm, but not the nuclei, of LECs of uninjured lenses was immunoreactive for Smads3/4. In contrast, nuclear immunoreactivity for Smads3/4 was detected in LECs during capsular healing. Nuclei positive for Smads3/4 were observed in monolayered LECs adjacent to the regenerated lens fibres of Sommerring’s ring. Interestingly, the nuclei of LECs that were somewhat elongated, and appeared to be differentiating into fibre-like cells, were negative for Smads3/4. Fibroblast-like, spindle-shaped lens cells with nuclear immunoreactivity for nuclear Smads3/4 were occasionally observed in the extracellular matrix accumulated in capsular opacification. Exogenous TGFβ induced nuclear translocation of Smad3 in LECs of anterior capsule specimens in explant culture.

Conclusions: This is consistent with TGFβ induced Smad signalling being involved in regulating the behaviour of LECs during wound healing after cataract surgery.

Keywords: lens epithelial cell, transforming growth factor β, Smad, cataract surgery

Abstract

Cytokines are thought to orchestrate the behaviour of lens epithelial cells during healing after cataract extraction. In many cases this results in aberrant growth of residual lens epithelial cells and the formation of fibrotic scar tissue (posterior capsular opacification, also referred to as secondary cataract or after-cataract).^1–⁶ Transforming growth factor β (TGFβ), mainly TGFβ2, is abundant in the aqueous humour.^7–⁹ TGFβ is pivotal in regulating proliferation, differentiation, and extracellular matrix (ECM) expression by cells in a positive or negative manner.^10,¹¹ Lens cells express TGFβ isoforms and TGFβ receptors.^12–¹⁵ Moreover, we have reported that human lens epithelial cells and macrophages adhering to implanted intraocular lenses (IOLs) express TGFβ family members.^15–¹⁷

Smads are proteins involved in mediating intracellular signal transduction between TGFβ/bone morphogenic protein (BMP) receptors and gene promoters,^18,¹⁹ although other signalling pathways have also been reported.²⁰ On ligand binding to the TGFβ receptor, phosphorylated Smad2 or Smad3 translocates to the nucleus in a complex with Smad4, and binds to a site in a promoter region. We observed that Smads3/4 translocate to the nuclei of lens epithelial cells in the healing murine lens following an anterior capsular injury. This is also the case in lens epithelial cells from murine lenses organ cultured in the presence of TGFβ2. Taken together this indicates that healing murine lens cells are regulated by endogenous TGFβ2 through the Smad system.¹⁴ We hypothesised that human lens epithelial cells are also regulated by endogenous TGFβ during healing following cataract extraction and implantation of an IOL. To explore this hypothesis, in the present study we examined Smads3/4 localisation in lens cells in postoperative lens capsule specimens from humans. We also examined phenotypic alterations in lens cells by immunodetection of β-crystallin and α-smooth muscle actin (αSMA), these being key markers for lens fibres and myofibroblastic cells respectively.^21–²³

Acknowledgments

The authors thank the members of IOL Implant Data System Committee of the Japanese Society of Cataract and Refractive Surgery for providing specimens.

Acknowledgments

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