Circadian variations of transforming growth factor-beta2 and basic fibroblast growth factor in the rabbit aqueous humor

Circadian CLOCK Mediates Activation of Transforming Growth Factor-β Signaling and Renal Fibrosis through Cyclooxygenase 2

The circadian rhythm regulates blood pressure and maintains fluid and electrolyte homeostasis with central and peripheral clock. However, the role of circadian rhythm in the pathogenesis of tubulointerstitial fibrosis remains unclear. Here, we found that the amplitudes of circadian rhythm oscillation in kidneys significantly increased after unilateral ureteral obstruction. In mice that are deficient in the circadian gene Clock, renal fibrosis and renal parenchymal damage were significantly worse after ureteral obstruction. CLOCK-deficient mice showed increased synthesis of collagen, increased oxidative stress, and greater transforming growth factor-β (TGF-β) expression. TGF-β mRNA expression oscillated with the circadian rhythms under the control of CLOCK-BMAL1 heterodimers. The expression of cyclooxygenase 2 was significantly higher in kidneys from CLOCK-deficient mice with ureteral obstruction. Treatment with a cyclooxygenase 2 inhibitor celecoxib significantly improved renal fibrosis in CLOCK-deficient mice. Taken together, these data establish the importance of the circadian rhythm in tubulointerstitial fibrosis and suggest CLOCK/TGF-β signaling as a novel therapeutic target of cyclooxygenase inhibition.

Retinal and choroidal TGF-beta in the tree shrew model of myopia: isoform expression, activation and effects on function

A visually evoked signalling cascade, which begins in the retina, transverses the choroid, and mediates scleral remodelling, is considered to control eye growth. The ubiquitous cytokine TGF-beta has been associated with alterations in ocular growth, where alterations in scleral TGF-beta isoforms mediate the scleral remodelling that results in myopia. However, while the TGF-beta isoforms have been implicated in the scleral change during myopia development, it is unclear whether alterations in retinal and choroidal isoforms constitute part of the retinoscleral cascade. This study characterised the retinal and choroidal TGF-beta isoform profiles and TGF-beta2 activation during different stages of myopia development, as induced by form deprivation, in a mammalian model of eye growth. Using quantitative real-time PCR, the mRNA for all three mammalian isoforms of TGF-beta was detected in tree shrew retina and choroid. Distinct tissue-specific isoform profiles were observed for the retina (TGF-beta1:TGF-beta2:TGF-beta3=20:2085:1) and choroid (TGF-beta1:TGF-beta2:TGF-beta3=16:23:1), which remained constant over the development period under investigation. The active and latent pools of retinal TGF-beta2 were quantified using ELISA with the majority (>94%) of total TGF-beta2 found in the latent form. Unlike previous scleral data showing early and continuous decreases in TGF-beta isoform expression during myopia development, the levels of the three isoforms remained within normal ranges for retinal (TGF-beta1, -14 to +14%; TGF-beta2, -2 to +20%; TGF-beta3, -10 to +26%) and choroidal (TGF-beta1, -19 to +21%; TGF-beta2, -26 to +8%; TGF-beta3, -11 to +28%) tissues during myopia development (induction times of 3h, 7h, 11h, 24h, and 5 days). A 40% decrease in retinal TGF-beta2 activation was observed after 5 days of myopia development, however, there was no functional correlate of altered TGF-beta2 activity, as assessed by the retinal ERG response. Overall, these data highlight the specific nature of TGF-beta isoform expression, which reflects the differences in tissue structure and function. While TGF-beta isoforms are involved in scleral regulation during myopia development in mammals, they do not have a primary role in the retinal and choroidal signals. Thus, the regulation of eye growth via the retinoscleral cascade involves more than one factor, which is likely to be tissue-specific in nature.

Direct effect of light on 24-h variation of aqueous humor protein concentration in Sprague-Dawley rats

Sprague-Dawley rats 10-12 weeks of age were entrained to a standard light-dark cycle with lights turned on at 6 am and off at 6 pm. Variations of 24-h aqueous humor protein concentration were determined. Samples were taken every 4h (N=10-14) under the standard light-dark condition at 8 pm, midnight, 4 am, 8 am, noon, and 4 pm. Under an acute constant dark condition, when lights were not turned on at 6 am, samples were collected at 8 am, noon, 4 pm, and 8 pm. Aqueous humor protein concentrations under the standard light-dark condition were found in the range of 0.305+/-0.115 mg/ml (mean+/-SD, N=10) at midnight to 1.505+/-0.342 mg/ml (N=14) at noon. The 3 light-phase protein concentrations were each higher than the 3 dark-phase concentrations. Aqueous humor protein concentrations at 8 am, noon, and 4 pm under the acute constant dark condition were each higher than the concentrations at 8 pm (after both 2h and 26 h in the dark), midnight, and 4 am, demonstrating an endogenously driven 24-h pattern. At 8 am, noon, and 4 pm, protein concentrations were 56-147% higher when exposed to light. Intraocular pressure (IOP) was monitored using telemetry in separate groups of light-dark entrained rats under the standard light-dark condition and the acute constant dark condition. The 24-h IOP pattern was inverse to the 24-h pattern of aqueous humor protein concentration under the standard light-dark condition, and this IOP pattern was not altered by the acute constant dark condition. In conclusion, an endogenously driven 24-h variation of aqueous humor protein concentration occurred in Sprague-Dawley rats with higher concentrations during the light-phase than the dark-phase. This endogenous pattern of protein concentration was accentuated by a direct effect of light, which was unrelated to the 24-h pattern of IOP.

Proteomics of the aqueous humor in healthy New Zealand rabbits

There are several physiological roles postulated for aqueous humor, a liquid located in the anterior and posterior chamber of the eye, such as maintenance of the intraocular pressure, provision of nutrients, and removal of metabolic waste from neighboring tissues and provision of an immune response and protection during inflammation and infection. To link these function to specific or classes of proteins, identification of the aqueous humor proteome is essential. Aqueous humor obtained from healthy New Zealand white rabbits was analyzed using three synergistic protein separation methods: 1-D gel electrophoresis, 2-DE, and 1-DLC (RPLC) prior to protein identification by MS. As each of these separation methods separates intact proteins based on different physical properties (pIs, molecular weights, hydrophobicity, solubility, etc.) the proteome coverage is expanded. This was confirmed, since overlap between all three separation technologies was only about 8.2% with many proteins found uniquely by a single method. Although the most dominant protein presented in normal aqueous humor is albumin, by using this extensive separation/MS strategy, additional proteins were identified in total amount of 98 nonredundant proteins (plus an additional ten proteins for consideration). This expands the current protein identifications by approximately 65%. The aqueous humor proteome comprises a specific selection of cellular and plasma based proteins and can almost exclusively be divided into four functional groups: cell-cell interactions/wound healing, proteases and protease inhibitors, antioxidant protection, and antibacterial/anti-inflammatory proteins.

The role of mammalian circadian proteins in normal physiology and genotoxic stress responses

The last two decades have significantly advanced our understanding of the organization of the circadian system at all levels of regulation-molecular, cellular, tissue, and systemic. It has been recognized that the circadian system represents a complex temporal regulatory network, which plays an important role in synchronizing various biological processes within an organism and coordinating them with the environment. It is believed that deregulation of this synchronization may result in the development of various pathologies. However, recent studies using various circadian mutant mouse models have demonstrated that at least some of the components of the molecular oscillator are actively involved in physiological processes not directly related to their role in the circadian clock. The growing amount of evidence suggests that, in addition to their circadian function, circadian proteins are important in maintaining tissue homeostasis under normal and stress conditions. In this chapter, we will summarize recent data about the regulation of the mammalian molecular circadian oscillator and will focus on a new role of the circadian system and individual circadian proteins in the organism's physiology and response to genotoxic stress in connection with diseases treatment and prevention.

Circadian clock genes as modulators of sensitivity to genotoxic stress

A broad variety of organisms display circadian rhythms (i.e., oscillations with 24-hr periodicities) in many aspects of their behavior, physiology and metabolism. These rhythms are under genetic control and are generated endogenously at the cellular level. In mammals, the core molecular mechanism of the oscillator consists of two transcriptional activators, CLOCK and BMAL1, and their transcriptional targets, CRYPTOCHROMES (CRYS) and PERIODS (PERS). The CRY and PER proteins function as negative regulators of CLOCK/BMAL1 activity, thus forming the major circadian autoregulatory feedback loop. It is believed that the circadian clock system regulates daily variations in output physiology and metabolism through periodic activation/repression of the set of clock-controlled genes that are involved in various metabolic pathways. Importantly, circadian-controlled pathways include those that determine in vivo responses to genotoxic stress. By using circadian mutant mice deficient in different components of the molecular clock system, we have established genetic models that correlate with the two opposite extremes of circadian cycle as reflected by the activity of the CLOCK/BMAL1 transactivation complex. Comparison of the in vivo responses of these mutants to the chemotherapeutic drug, cyclophosphamide (CY), has established a direct correlation between drug toxicity and the functional status of the CLOCK/BMAL1 transcriptional complex. We have also demonstrated that CLOCK/BMAL1 modulates sensitivity to drug-induced toxicity by controlling B cell responses to active CY metabolites. These results suggest that the sensitivity of cells to genotoxic stress induced by anticancer therapy may be modulated by CLOCK/BMAL1 transcriptional activity. Further elucidation of the molecular mechanisms of circadian control as well as identification of specific pharmacological modulators of CLOCK/BMAL1 activity are likely to lead to the development of new anti-cancer treatment schedules with increased therapeutic index and reduced morbidity.

The human FGF2 level is influenced by genetic predisposition

BACKGROUND

The fibroblast growth factor 2 (FGF2) is involved in various processes possibly leading to the development of complex diseases such as atherosclerosis. In recent studies, its cardioprotective properties, due to its ability to stimulate the proliferation of collateral vessels, could be shown.

STUDY DESIGN

In this clinical study, the relation between clinical risk markers, a genomic variant of FGF2, namely the c.223C>T polymorphism, and the in vivo FGF2 expression was evaluated. Therefore, 198 clinically well-characterized probands, all of Caucasian origin, were included. The FGF2 mRNA level was determined in monocytes by competitive RT-PCR, whereas the plasma level of circulating FGF2 protein was analysed by ELISA. By considering the angiographically proven stenotic state of the patient, a significant increase in FGF2 mRNA, but not in protein level, could be shown for patients with significant stenosis. Apart from this, no influence on FGF2 expression was found in the case of all of the clinical and biochemical markers investigated. However, in the case of the c.223C>T polymorphism, a significant increase in the individual FGF2 mRNA and protein level in CC-carriers was shown. In multivariate analysis, this relation was independent of all other risk markers investigated.

CONCLUSIONS

Our results suggest that an increase in FGF2 mRNA expression, related to coronary atherosclerosis, may be necessary for the maintenance of the individual FGF2 plasma level. Since the individual FGF2 mRNA and protein level are, to a large extent, triggered off by genetic background, the FGF2 expression cannot be referred to as an independent clinical marker for CAD.

Circadian sensitivity to the chemotherapeutic agent cyclophosphamide depends on the functional status of the CLOCK/BMAL1 transactivation complex

The circadian clock controls many aspects of mammalian physiology, including responses to cancer therapy. We find that wild-type and circadian mutant mice demonstrate striking differences in their response to the anticancer drug cyclophosphamide (CY). While the sensitivity of wild-type mice varies greatly, depending on the time of drug administration, Clock mutant and Bmal1 knockout mice are highly sensitive to treatment at all times tested. On the contrary, mice with loss-of-function mutations in Cryptochrome (Cry1-/-Cry2-/- double knockouts) were more resistant to CY compared with their wild-type littermates. Thus, both time-of-day and allelic-dependent variations in response to chemotherapy correlate with the functional status of the circadian CLOCK/BMAL1 transactivation complex. Pharmacokinetic analysis of plasma concentration of different CY metabolites shows that, in contrast to the traditional view, circadian variations in drug sensitivity cannot be attributed to the changes in the rates of CY metabolic activation and/or detoxification. At the same time, mice of different circadian genotypes demonstrate significant differences in B cell responses to toxic CY metabolites: B cell survival/recovery rate was directly correlated with the in vivo drug sensitivity. Based on these results, we propose that the CLOCK/BMAL1 transcriptional complex affects the lethality of chemotherapeutic agents by modulating the survival of the target cells necessary for the viability of the organism.