Calpain Expression and Activity during Lens Fiber Cell Differentiation

Abstract

In animal models, the dysregulated activity of calcium-activated proteases, calpains, contributes directly to cataract formation. However, the physiological role of calpains in the healthy lens is not well defined. In this study, we examined the expression pattern of calpains in the mouse lens. Real time PCR and Western blotting data indicated that calpain 1, 2, 3, and 7 were expressed in lens fiber cells. Using controlled lysis, depth-dependent expression profiles for each calpain were obtained. These indicated that, unlike calpain 1, 2, and 7, which were most abundant in cells near the lens surface, calpain 3 expression was strongest in the deep cortical region of the lens. We detected calpain activities in vitro and showed that calpains were active in vivo by microinjecting fluorogenic calpain substrates into cortical fiber cells. To identify endogenous calpain substrates, membrane/cytoskeleton preparations were treated with recombinant calpain, and cleaved products were identified by twodimensional difference electrophoresis/mass spectrometry. Among the calpain substrates identified by this approach was ␣II-spectrin. An antibody that specifically recognized calpaincleaved spectrin was used to demonstrate that spectrin is cleaved in vivo, late in fiber cell differentiation, at or about the time that lens organelles are degraded. The generation of the calpain-specific spectrin cleavage product was not observed in lens tissue from calpain 3-null mice, indicating that calpain 3 is uniquely activated during lens fiber differentiation. Our data suggest a role for calpains in the remodeling of the membrane cytoskeleton that occurs with fiber cell maturation.

Biological glass: structural determinants of eye lens transparency

“…Recently, it has emerged that calpains also play a role in the normal process of fibre cell differentiation. Antibodies raised against calpain-cleaved spectrin label specifically lens fibre cells adjacent to the OFZ [34]. The calpain-dependent fragmentation of spectrin in this cohort of cells is direct evidence that one or more calpains are activated in this region of the lens.…”

“…Although studies have failed to show that caspase activation accompanies organelle breakdown, another class of cysteine proteases, calpains, are activated [34]. Calpains have long been known to be activated in the lens under pathological conditions of calcium overload and have been suspected of playing a role in human cataract formation.…”

Risk of cataract and glaucoma in patients with multiple sclerosis

“…8 Calpain 1 (µ-calpain), the lens-specific isoenzyme Lp85, calpain 2 (m-calpain), calpain 3, calpain 10 and the lens-specific Abbreviations: HR, Hazard Ratio; CI, Confidence Interval; N, number of cataract/glaucoma patients # : referent: patients without multiple sclerosis; adjusted for age and gender, smoking, body mass index, systemic glucocorticoids (unless stratified), hypnotics/anxiolytics, anticonvulsants (unless stratified), antidepressants use 6 months prior, diabetes mellitus, chronic obstructive pulmonary disease, cerebrovascular disease, epilepsy and any ocular surgery ever before & : referent: patients without multiple sclerosis; adjusted for age and gender, smoking, body mass index, systemic glucocorticoids (unless stratified), anticonvulsants (unless stratified), serotonin-selective reuptake inhibitors, tricyclic antidepressants, ocular glucocorticoids (unless stratified) use 6 months prior, cerebrovascular disease, epilepsy and any uveitis ever before § : Statistically significant difference (p < 0.05) of the exposure to the medication versus non-exposure to the medication ¥ : Statistically significant difference (p < 0.05) of the exposure to the disease versus non-exposure to the disease isoenzyme Lp82 are known to be active in the lens, with calpain 2 being the most prevalent in mammalian cells. 6,26 In the presence of elevated calcium ion (Ca 2+ ) levels, overactivation of calpains is thought to cause the degradation of lens proteins and changes in the cytoskeletal architecture. 6,7,26 These morphological and biological changes then result in the formation of cataract.…”

“…6,26 In the presence of elevated calcium ion (Ca 2+ ) levels, overactivation of calpains is thought to cause the degradation of lens proteins and changes in the cytoskeletal architecture. 6,7,26 These morphological and biological changes then result in the formation of cataract. Lower oestrogen levels in men versus women may explain why the risk in young men is increased compared with young women.…”

“…5 Lens membrane functions are altered, resulting in cataract formation. 6,7 Imam et al measured a significantly increased activity of proteolytic enzymes in patients with MS during a relapse. 8 Other studies showed that cataracts are caused by intraocular inflammation of the uveal tract, [9][10][11] which can be a complication in patients with MS. 12 Risk of cataract and glaucoma in patients with multiple sclerosis 39 …”