Activation of the unfolded protein response in aged human lenses.

Cataract formation is a multifactorial disease, induced by a variety of stressors. The endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR) is known to produce reactive oxygen species (ROS) leading to apoptosis. The present study aimed to investigate whether activation of the UPR occurs in human lenses, using human lens epithelial cell (HLEC) lines and lenses obtained from an eye bank, from individuals aged between 50 and 90 years. In vitro analysis was performed using calcimycin (10 µM) as an ER stressor. The level of ER stress was measured by the production of ROS, staining for cell death, detection of binding immunoglobulin proteins (BIP) and levels of other UPR proteins, including inositol-requiring enzyme-1 (IRE), activating transcription factor (ATF) 6 and PKR-like eukaryotic initiation factor 2a kinase (PERK). These parameters were examined in HLECs exposed to calcimycin for 12, 24, 48 and 72 h. Fluorescent activated cell sorting analysis of the levels of ROS and apoptosis revealed an increase following 24 h calcimycin exposure. The reverse transcription quantitative polymerase chain reaction results demonstrated a gradual increase in the mRNA levels of BIP, IRE1, ATF6 and PERK between 12 and 72 h. A similar effect was observed in the protein levels, which also demonstrated a gradual increase in the levels of endoplasmic oxidoreductin-1-like (Ero1-L)-ß and protein disulfide isomerase, but a lower level of Ero1-Lα. Activation of the UPR involved the apoptotic pathway, revealed by increased levels of C/EBP homologous protein, ATF4 and caspase-4. Additionally, the antioxidant protein levels were also suppressed. The investigation of aged human lenses revealed a similar increase in the protein expression of UPR. These results indicated that activation of the UPR­induced ROS production suppressed the antioxidant status and triggered the apoptotic pathway, ultimately leading to the formation of age-related cataracts.

Evaluation of the effects of systemic treatment with a sclerostin neutralizing antibody on bone repair in a rat femoral defect model.

Systemic administration of a sclerostin neutralizing antibody (Scl-Ab) has been shown to enhance fracture callus density and strength in several animal models. In order to further evaluate the potential of Scl-Ab to improve healing in a bone defect model,we evaluated Scl-Ab in a 3mm femoral defect in young male outbred rats. Scl-Ab was given either continuously for 6 or 12 weeks after surgery or with 2 weeks of delay for 10 weeks. Bone formation was assessed by radiographs, µ-CT, and histology. Complete bony union was achieved in only a few defects after 12 weeks of healing (Scl-Ab treated 5/30, vehicle treated 1/15). µ-CT evaluation demonstrated a significant increase in the BV/TV in the defect in the delayed treatment group (65%, p<0.05), but a non-significant increase in the continuous group (35%, p = 0.11) compared to control. However, both regimens induced an anabolic response in the bone proximal and distal to the defect and in the un-operated femurs. We demonstrate that treatment with Scl-Ab can enhance bone repair in a bone defect and in the surrounding host bone, but lacks the osteoinductive activity to heal it. This agent seems to be most effective in bone repair scenarios where there is cortical integrity.

Systemic administration of sclerostin antibody enhances bone repair in a critical-sized femoral defect in a rat model.

BACKGROUND: Systemic administration of sclerostin neutralizing antibody has led to increased bone formation in animal models of osteoporosis. The purpose of this study was to determine if systemic administration of sclerostin neutralizing antibody could increase the healing response in a critical-sized femoral defect in rats. METHODS: Critical-sized femoral defects were created in Lewis rats, and the rats were randomized into four groups. The sclerostin antibody (Scl-Ab) treatment groups included the continuous Scl-Ab group (twenty-one animals), the early Scl-Ab group (fifteen animals), and the delayed Scl-Ab group (fifteen animals), which received sclerostin antibody (25 mg/kg) twice weekly for weeks 0 through 12; weeks 0 through 2; and weeks 2 through 4; respectively. Twenty-one animals in the control group received vehicle from weeks 0 through 12. In a subsequent study, bone turnover markers were measured at zero, two, six, and twelve weeks after surgery in rats receiving vehicle or sclerostin neutralizing antibody for twelve weeks (fifteen rats per group). The quality of bone formed was evaluated with radiographs, microcomputed tomography, biomechanical testing, and histologic and histomorphometric analysis. RESULTS: In the primary study, four of fifteen defects in the continuous (zero to twelve-week) Scl-Ab group, three of fifteen defects in the early (zero to two-week) Scl-Ab group, and four of fifteen defects in the delayed (two to four-week) Scl-Ab group healed at twelve weeks, while none of the defects healed in the control group. In both studies, treatment with sclerostin antibody for twelve weeks demonstrated a significant increase in new bone formation (p < 0.05) compared with the control group. The three treatment groups did not differ significantly with respect to the healing rates and the quality of new bone formed in the defect. The serum markers of bone formation were significantly elevated in the animals in the continuous Scl-Ab group (p < 0.05) compared with the controls. CONCLUSIONS: Administration of sclerostin neutralizing antibody led to increased bone formation, resulting in complete healing of femoral defects in a small subset of rats, with a majority of the animals not healing the defect by twelve weeks.