Effects of long-term diabetes and galactosaemia upon lens and retinal mRNA levels in the rat

Evaluation of the possibility of selective modulation of retinal glucose transporters in diabetic complications: An experimental study

PURPOSE:

To identify the possibility of modulating retinal glucose transporters in diabetic conditions to prevent retinal complications of diabetic retinopathy.

MATERIALS AND METHODS:

In silico and in vitro binding assays were performed to assess the effect of genistein and positive controls (pioglitazone and estradiol) on nuclear receptor estrogen receptor beta and peroxisome proliferator-activated receptor gamma (PPARγ). In vivo effects of compounds were tested on diabetic rats. Structural and functional analysis of retina was performed at 28^th day followed by gene expression analysis of glucose transporters and nuclear receptors. Pioglitazone and genistein levels were analyzed by liquid chromatography with tandem mass spectrometry.

RESULTS:

Genistein showed equi-affinity toward PPARγ in In silico experiments contrary to in vitro findings. In multidose study, their therapeutic effects were observed by analyzing the retinal function. Retinal gene expression studies revealed that both test agents significantly up regulated PPARγ, GLUT4, and down regulated GLUT1. Genistein showed significant up regulation of GLUT4 and down regulation of GLUT1 as compared to PGZ which has been well correlated with the Electroretinography (ERG) outcome.

CONCLUSION:

This study showed the possibility of selective upregulation of GLUT4 (independent of PPARγ activation) in the retina of diabetic rats using genistein. Selective modulation of retinal glucose transporters as therapeutic target in ocular diabetic complications can be possibly explored.

Gene cloning to clinical trials-the trials and tribulations of a life with collagen

This review, based on the BSMB Fell-Muir Lecture I presented in July 2018 at the Matrix Biology Europe Conference in Manchester, gives a personal perspective of my own laboratory's contributions to research into type X collagen, metaphyseal chondrodysplasia type Schmid and potential treatments for this disorder that are currently entering clinical trial. I have tried to set the advances made in the context of the scientific technologies available at the time and how these have changed over the more than three decades of this research.

Focusing on Sodium Glucose Cotransporter-2 and the Sympathetic Nervous System: Potential Impact in Diabetic Retinopathy

The prevalence of diabetes is at pandemic levels in today's society. Microvascular complications in organs including the eye are commonly observed in human diabetic subjects. Diabetic retinopathy (DR) is a prominent microvascular complication observed in many diabetics and is particularly debilitating as it may result in impaired or complete vision loss. In addition, DR is extremely costly for the patient and financially impacts the economy as a range of drug-related therapies and laser treatment may be essential. Prevention of microvascular complications is the major treatment goal of current therapeutic approaches; however, these therapies appear insufficient. Presently, sodium glucose cotransporter-2 (SGLT2) inhibitors may offer a novel therapy beyond simple glucose lowering. Excitingly, the EMPA-REG clinical trial, which focuses on the clinically used SGLT2 inhibitor empagliflozin, has been extremely fruitful and has highlighted beneficial cardiovascular and renal outcomes. The effects of SGLT2 inhibitors on DR are currently a topic of much research as outlined in the current review, but future studies are urgently needed to fully gain mechanistic insights. Here, we summarize current evidence and identify gaps that need to be addressed.

Glucose transport in brain and retina: implications in the management and complications of diabetes

Neural tissue is entirely dependent on glucose for normal metabolic activity. Since glucose stores in the brain and retina are negligible compared to glucose demand, metabolism in these tissues is dependent upon adequate glucose delivery from the systemic circulation. In the brain, the critical interface for glucose transport is at the brain capillary endothelial cells which comprise the blood-brain barrier (BBB). In the retina, transport occurs across the retinal capillary endothelial cells of the inner blood-retinal barrier (BRB) and the retinal pigment epithelium of the outer BRB. Because glucose transport across these barriers is mediated exclusively by the sodium-independent glucose transporter GLUT1, changes in endothelial glucose transport and GLUT1 abundance in the barriers of the brain and retina may have profound consequences on glucose delivery to these tissues and major implications in the development of two major diabetic complications, namely insulin-induced hypoglycemia and diabetic retinopathy. This review discusses the regulation of brain and retinal glucose transport and glucose transporter expression and considers the role of changes in glucose transporter expression in the development of two of the most devastating complications of long-standing diabetes mellitus and its management.

Levels and molecular size distribution of serum laminin in adult type I diabetic patients with and without microangiopathy

The glycoprotein laminin, a cross-shaped complex of three genetically different polypeptide chains, is a structural component of the capillary basement membrane. Serum laminin concentrations of healthy controls (n = 60) and adult type I diabetic patients (n = 170) were not age-dependent. Laminin was correlated with hemoglobin A1 (HbA1) values in normoalbuminuric patients (rs = .33, P < .0005, n = 116). Type I diabetic patients without nephropathy or retinopathy in good metabolic control had normal laminin levels. However, increasing stages of microangiopathy were associated with higher laminin levels. The molecular size distribution of serum laminin of control subjects (n = 4) and type I diabetic patients (n = 15) was analyzed by molecular-sieve chromatography. Laminin was eluted in two peaks with a molecular mass of 900 and 300 kd, most likely representing intact laminin and its P1 fragment, respectively. The areas of the two peaks were determined by two-gaussian function fitting. In patients without microangiopathy in poor metabolic control, an increase in the high-molecular weight (HMW) fraction could be detected as compared with healthy subjects and patients with acceptable metabolic control. Furthermore, the HMW laminin fraction and the ratio between the areas of the first and second peak increased with the stage of nephropathy (P < .001, Jonckheere-Terpstra test). These results provide evidence that (1) laminin concentration is increased in chronic hyperglycemia, (2) laminin may be a marker of microangiopathic lesions, and (3) elevated laminin levels may reflect an increased synthesis and/or a defective incorporation of laminin into the capillary basement membrane.

Expression of laminin and type IV collagen by basement membrane-producing EHS tumors in streptozotocin-induced diabetic mice: in vivo modulation by low-molecular-weight heparin fragments

The biosynthesis of basement membrane components in Engelberth Holm Swarm-bearing mice with or without streptozotocin-induced diabetes and the effect of low-molecular-weight heparin derivatives (CY222, Sanofi Recherche/Institut Choay) on the relative rates of these synthetic activities were studied. In diabetic mice, the laminin mRNA level increased, whereas type IV collagen mRNA decreased. In vivo treatment with heparin fragments decreased the mRNA level of laminin to control values without altering the mRNA level of collagen IV. Biosynthetic studies with radiolabeled precursors ([3H]-proline for collagen and [35S]-methionine for laminin) confirmed these results. Laminin protein biosynthesis increased in diabetic mice. Treatment with CY222 corrected this alteration. Our results suggested an increased labeling of polymeric forms of collagen IV in diabetic mice. In addition, we showed that biosynthesis of acid-extractable collagen IV decreased in diabetic mice and that CY222 treatment corrected this disturbance. These experiments suggest that low-molecular-weight heparin fragments CY222 can modulate the biosynthesis of extracellular matrix macromolecules altered in diabetic animals by different pathways, including pretranslational and posttranslational steps.

Increased expression of basement membrane collagen in human diabetic retinopathy

Basement membrane thickening is the most prominent and characteristic feature of early diabetic microangiopathy. Unknown is not only the causative process but also whether the thickening reflects increased synthesis of specific components. Because collagen type IV is uniquely present in basement membranes and represents their predominant structural element, we studied its expression in retinas obtained postmortem from five patients with 8 +/- 3 yr of diabetes and six nondiabetic controls. The collagen IV transcript proved to be rare in adult human retina and undetectable by Northern analysis. We thus identified a set of primers and conditions to detect the transcript by the reverse transcriptase polymerase chain reaction and to measure its level relative to an endogenous internal standard (beta-actin mRNA). In the diabetic patients the levels of collagen IV mRNA were increased twofold over levels in controls, whereas the actin mRNA levels were similar in the two groups. Hence, the collagen IV/actin ratio was 0.53 +/- 0.15 in diabetic samples and 0.24 +/- 0.09 in control samples (P = 0.004). These results indicate that diabetes induces a twofold increase in the expression of collagen IV by the cells that synthesize basement membranes in the adult retina (vascular cells). Insofar as high ambient glucose in vitro elicits the same effect, it may be proposed that basement membrane thickening in diabetes results from enhanced synthesis of specialized component molecules sustained by hyperglycemia.

Dose-dependent alterations in nerve polyols and (Na+,K+)-ATPase activity in galactose intoxication

Nerve polyol content and (Na+,K+)-adenosine triphosphatase (ATPase) activity of nerve homogenates were studied in a colony of rats fed diets containing either 0%, 10%, 20%, or 40% galactose for 4 months. Nerve water and dulcitol content exhibited dose-dependent increases, whereas nerve myo-inositol content declined with increasing dietary galactose. Homogenate (Na+,K+)-ATPase activity increased with increasing galactose consumption of up to 20% dietary intake and thereafter remained consistently elevated at twice the activity of 0% galactose-fed values. Nerves of rats fed 40% galactose were also examined at the light microscope level and showed evidence of both edema and myelin splitting. These data demonstrate that increased nerve water content, dulcitol accumulation, and myo-inositol depletion parallel the previously reported dose-related increase of endoneurial fluid sodium and chloride in nerves of galactose-fed rats and suggest that elevated nerve homogenate (Na+,K+)-ATPase activity may be related to one or more of these consequences of exaggerated polyol pathway flux.

Dopamine D2-receptor mRNA level in rat striatum after chronic haloperidol treatment

Chronic treatment with haloperidol, a D2-receptor antagonist and a neuroleptic, increases the number of D2-receptors in rat striatum. However, there have been inconsistent reports on the D2-receptor mRNA level, one showing the increase in the mRNA level and another detecting no changes. Furthermore, they did not distinguish the two isoforms of D2-receptor, D2A and D2B. In the present work, both D2- and DeA-receptor mRNA levels in rat striatum were estimated after chronic administration of haloperidol. There was, within the sensitivity of the assay, no significant increase in either of them between 3 and 24 h after the last administration. This suggests that chronic haloperidol treatment does not affect the transcriptional regulation of the D2-receptor gene or the alternative splicing process of its transcripts.