Peptain-1 blocks ischemia/reperfusion-induced retinal capillary degeneration in mice.

Introduction: Neurovascular degeneration results in vascular dysfunction, leakage, ischemia, and structural changes that can lead to significant visual impairment. We previously showed the protective effects of peptain-1, a 20 amino acid peptide derived from the αB-crystallin core domain, on retinal ganglion cells in two animal models of glaucoma. Here, we evaluated the ability of peptain-1 to block apoptosis of human retinal endothelial cells (HRECs) and retinal capillary degeneration in mice subjected to retinal ischemia/reperfusion (I/R) injury.

Mechanisms contributing to inhibition of retinal ganglion cell death by cell permeable peptain-1 under glaucomatous stress.

This study assesses the neuroprotective potential of CPP-P1, a conjugate of an anti-apoptotic peptain-1 (P1) and a cell-penetrating peptide (CPP) in in vitro, in vivo, and ex vivo glaucoma models. Primary retinal ganglion cells (RGCs) were subjected to either neurotrophic factor (NF) deprivation for 48 h or endothelin-3 (ET-3) treatment for 24 h and received either CPP-P1 or vehicle. RGC survival was analyzed using a Live/Dead assay.

Quantifying Protein Acetylation in Diabetic Nephropathy from Formalin-Fixed Paraffin-Embedded Tissue.

Purpose: Diabetic kidney disease (DKD) is a serious complication of diabetes mellitus and a leading cause of chronic kidney disease and end-stage renal disease. One potential mechanism underlying cellular dysfunction contributing to kidney disease is aberrant protein post-translational modifications. Lysine acetylation is associated with cellular metabolic flux and is thought to be altered in patients with diabetes and dysfunctional renal metabolism.

Thiol-Mediated Enhancement of N-Acetyllysine Formation in Lens Proteins.

Lysine acetylation (AcK) is a prominent post-translational modification in eye lens crystallins. We have observed that AcK formation is preferred in some lysine residues over others in crystallins. In this study, we have investigated the role of thiols in such AcK formation.

Aggrelyte-2 promotes protein solubility and decreases lens stiffness through lysine acetylation and disulfide reduction: Implications for treating presbyopia.

Aging proteins in the lens become increasingly aggregated and insoluble, contributing to presbyopia. In this study, we investigated the ability of aggrelyte-2 (N,S-diacetyl-L-cysteine methyl ester) to reverse the water insolubility of aged human lens proteins and to decrease stiffness in cultured human and mouse lenses. Water-insoluble proteins (WI) of aged human lenses (65-75 years) were incubated with aggrelyte-2 (500 μM) for 24 or 48 h.

Peptains block retinal ganglion cell death in animal models of ocular hypertension: implications for neuroprotection in glaucoma.

Ocular hypertension is a significant risk factor for vision loss in glaucoma due to the death of retinal ganglion cells (RGCs). This study investigated the effects of the antiapoptotic peptides peptain-1 and peptain-3a on RGC death in vitro in rat primary RGCs and in mouse models of ocular hypertension. Apoptosis was induced in primary rat RGCs by trophic factor deprivation for 48 h in the presence or absence of peptains.

AAV2-Mediated Expression of HspB1 in RGCs Prevents Somal Damage and Axonal Transport Deficits in a Mouse Model of Ocular Hypertension.

Purpose: Ocular hypertension is a significant risk factor for vision loss in glaucoma caused by the death of retinal ganglion cells (RGCs). We investigated whether small heat shock proteins (sHsps) expressed in RGCs protect those cells against ocular hypertension in mice.

Methods: AAV2 vectors encoding genes for one of the following four human sHsps: HSPB1, HSPB4, HSPB5, or HSPB6 were constructed for RGC-specific expression.

Small Heat Shock Proteins in Retinal Diseases.

This review summarizes the latest findings on small heat shock proteins (sHsps) in three major retinal diseases: glaucoma, diabetic retinopathy, and age-related macular degeneration. A general description of the structure and major cellular functions of sHsps is provided in the introductory remarks. Their role in specific retinal diseases, highlighting their regulation, role in pathogenesis, and possible use as therapeutics, is discussed.

Glycation-mediated protein crosslinking and stiffening in mouse lenses are inhibited by carboxitin in vitro.

Proteins in the eye lens have negligible turnover and therefore progressively accumulate chemical modifications during aging. Carbonyls and oxidative stresses, which are intricately linked to one another, predominantly drive such modifications. Oxidative stress leads to the loss of glutathione (GSH) and ascorbate degradation; this in turn leads to the formation of highly reactive dicarbonyl compounds that react with proteins to form advanced glycation end products (AGEs).

Glycation-mediated inter-protein cross-linking is promoted by chaperone-client complexes of α-crystallin: Implications for lens aging and presbyopia.

Lens proteins become increasingly cross-linked through nondisulfide linkages during aging and cataract formation. One mechanism that has been implicated in this cross-linking is glycation through formation of advanced glycation end products (AGEs). Here, we found an age-associated increase in stiffness in human lenses that was directly correlated with levels of protein-cross-linking AGEs.

Kynurenic Acid Protects Against Ischemia/Reperfusion-Induced Retinal Ganglion Cell Death in Mice.

Background: Glaucoma is an optic neuropathy and involves the progressive degeneration of retinal ganglion cells (RGCs), which leads to blindness in patients. We investigated the role of the neuroprotective kynurenic acid (KYNA) in RGC death against retinal ischemia/reperfusion (I/R) injury.

Methods: We injected KYNA intravenously or intravitreally to mice.

Lysine malonylation and propionylation are prevalent in human lens proteins.

Acylated lysine residues represent major chemical modifications in proteins. We investigated the malonylation and propionylation of lysine residues (MalK, PropK) in the proteins of aging human lenses. Western blot results showed that the two modifications are present in human lens proteins.

Systemically administered peptain-1 inhibits retinal ganglion cell death in animal models: implications for neuroprotection in glaucoma.

Axonal degeneration and death of retinal ganglion cells (RGCs) are the primary causes of vision loss in glaucoma. In this study, we evaluated the efficacy of a peptide (peptain-1) that exhibits robust chaperone and anti-apoptotic activities against RGC loss in two rodent models and in cultured RGCs. In cultures of rat primary RGCs and in rat retinal explants peptain-1 significantly decreased hypoxia-induced RGC loss when compared to a scrambled peptide.

The absence of SIRT3 and SIRT5 promotes the acetylation of lens proteins and improves the chaperone activity of α-crystallin in mouse lenses.

Acetylation of lysine residues occurs in lens proteins. Previous studies have shown an improvement in the chaperone activity of αA-crystallin upon acetylation. Sirtuins are NAD-dependent enzymes that can deacylate proteins.

Succinylation Is a Gain-of-Function Modification in Human Lens αB-Crystallin.

Acylation of lysine residues is a common post-translational modification of cellular proteins. Here, we show that lysine succinylation, a type of acylation, occurs in human lens proteins. All of the major crystallins exhibited N-succinyllysine (SuccK) residues.

A monoclonal antibody targeted to the functional peptide of αB-crystallin inhibits the chaperone and anti-apoptotic activities.

αB-Crystallin is a member of the small heat shock protein family. It is a molecular chaperone and an anti-apoptotic protein. Previous studies have shown that the peptide (DRFSVNLDVKHFSPEELKVKV, hereafter referred to as peptain-1) from the core domain of αB-crystallin exhibits both chaperone and anti-apoptotic properties similar to the parent protein.

The role of HIF-1α in the TGF-β2-mediated epithelial-to-mesenchymal transition of human lens epithelial cells.

Human lens epithelial cells (HLE) undergo mesenchymal transition and become fibrotic during posterior capsule opacification (PCO), which is a frequent complication after cataract surgery. TGF-β2 has been implicated in this fibrosis. Previous studies have focused on the role of hypoxia-inducible factor-1α (HIF-1α) in fibrotic diseases, but the role of HIF-1α in the TGF-β2-mediated fibrosis in HLE is not known.

The Absence of Indoleamine 2,3-Dioxygenase Inhibits Retinal Capillary Degeneration in Diabetic Mice.

Purpose: Loss of retinal capillary endothelial cells and pericytes through apoptosis is an early event in diabetic retinopathy (DR). Inflammatory pathways play a role in early DR, yet the biochemical mechanisms are poorly understood. In this study, we investigated the role of indoleamine 2,3-dioxygenase (IDO), an inflammatory cytokine-inducible enzyme, on retinal endothelial apoptosis and capillary degeneration in the diabetic retina.

αB-crystallin is essential for the TGF-β2-mediated epithelial to mesenchymal transition of lens epithelial cells.

Transforming growth factor (TGF)-β2-mediated pathways play a major role in the epithelial to mesenchymal transition (EMT) of lens epithelial cells (LECs) during secondary cataract formation, which is also known as posterior capsule opacification (PCO). Although αB-crystallin is a major protein in LEC, its role in the EMT remains unknown. In a human LEC line (FHL124), TGF-β2 treatment resulted in changes in the EMT-associated proteins at the mRNA and protein levels.

Therapeutic potential of α-crystallin.

Background: The findings that α-crystallins are multi-functional proteins with diverse biological functions have generated considerable interest in understanding their role in health and disease. Recent studies have shown that chaperone peptides of α-crystallin could be delivered into cultured cells and in experimental animals with beneficial effects against protein aggregation, oxidation, inflammation and apoptosis.

Scope Of Review: In this review, we will summarize the latest developments on the therapeutic potential of α-crystallins and their functional peptides.

Effects of photobleaching on selected advanced glycation end products in the human lens.

Background: Cataract is the leading cause of blindness, especially in the developing world. To ease access to treatment, we have proposed that cataract could be treated non-invasively by photobleaching of the chemically modified proteins responsible for cataract formation. The present study was aimed at examining the optical and biochemical effects of the proposed treatment.

Identification of peptides in human Hsp20 and Hsp27 that possess molecular chaperone and anti-apoptotic activities.

Previous studies have identified peptides in the 'crystallin-domain' of the small heat-shock protein (sHSP) α-crystallin with chaperone and anti-apoptotic activities. We found that peptides in heat-shock protein Hsp20 (G71HFSVLLDVKHFSPEEIAVK91) and Hsp27 (D93RWRVSLDVNHFAPDELTVK113) with sequence homology to α-crystallin also have robust chaperone and anti-apoptotic activities. Both peptides inhibited hyperthermic and chemically induced aggregation of client proteins.

Pro-inflammatory cytokines downregulate Hsp27 and cause apoptosis of human retinal capillary endothelial cells.

The formation of acellular capillaries in the retina, a hallmark feature of diabetic retinopathy, is caused by apoptosis of endothelial cells and pericytes. The biochemical mechanism of such apoptosis remains unclear. Small heat shock proteins play an important role in the regulation of apoptosis.