Antisense oligonucleotides modulate high glucose-induced laminin overexpression and cell proliferation: a potential for therapeutic application in diabetic microangiopathy

siRNA: an alternative treatment for diabetes and associated conditions

Diabetes is a condition that is not completely treatable but life of a diabetic patient can be smoothed by preventing or delaying the associate conditions like diabetic retinopathy, nephropathy, impaired wound healing process, etc. Apart from conventional methods to regulate diabetic condition, new techniques using siRNA have been emerged to prevent the associated conditions. This paper focuses on how siRNA used as a tool to silence the expression of genes which plays critical role in pathogenesis of these conditions. A marked improvement in wound-healing process of diabetic patients has been observed with siRNA treatment by silencing of Keap1 gene. Glucagon plays critical role in glucose homoeostasis and increases blood glucose level during hypoglycaemia. Glucose homoeostasis is impaired in diabetic patient and suppressing the expression of glucagon secretion with siRNA is used to suppress the progress of diabetes. Similarly, silencing expression of several factors has demonstrated improvement of treatment of diabetic nephropathy, retinopathy and inflammation by the use of siRNA.

Impaired Hedgehog signalling-induced endothelial dysfunction is sufficient to induce neuropathy: implication in diabetes

AIMS

Microangiopathy, i.e. endothelial dysfunction, has long been suggested to contribute to the development of diabetic neuropathy, although this has never been fully verified. In the present paper, we have identified the role of Hedgehog (Hh) signalling in endoneurial microvessel integrity and evaluated the impact of impaired Hh signalling in endothelial cells (ECs) on nerve function.

METHODS AND RESULTS

By using Desert Hedgehog (Dhh)-deficient mice, we have revealed, that in the absence of Dhh, endoneurial capillaries are abnormally dense and permeable. Furthermore, Smoothened (Smo) conditional KO mice clarified that this increased vessel permeability is specifically due to impaired Hh signalling in ECs and is associated with a down-regulation of Claudin5 (Cldn5). Moreover, impairment of Hh signalling in ECs was sufficient to induce hypoalgesia and neuropathic pain. Finally in Lepr(db/db) type 2 diabetic mice, the loss of Dhh expression observed in the nerve was shown to be associated with increased endoneurial capillary permeability and decreased Cldn5 expression. Conversely, systemic administration of the Smo agonist SAG increased Cldn5 expression, decreased endoneurial capillary permeability, and restored thermal algesia to diabetic mice, demonstrating that loss of Dhh expression is crucial in the development of diabetic neuropathy.

CONCLUSION

The present work demonstrates the critical role of Dhh in maintaining blood nerve barrier integrity and demonstrates for the first time that endothelial dysfunction is sufficient to induce neuropathy.

Extracellular matrix, gap junctions, and retinal vascular homeostasis in diabetic retinopathy

The vascular basement membrane (BM) contains extracellular matrix (ECM) proteins that assemble in a highly organized manner to form a supportive substratum for cell attachment facilitating myriad functions that are vital to cell survival and overall retinal homeostasis. The BM provides a microenvironment in which bidirectional signaling through integrins regulates cell attachment, turnover, and functionality. In diabetic retinopathy, the BM undergoes profound structural and functional changes, and recent studies have brought to light the implications of such changes. Thickened vascular BM in the retinal capillaries actively participate in the development and progression of characteristic changes associated with diabetic retinopathy. High glucose (HG)-induced compromised cell-cell communication via gap junctions (GJ) in retinal vascular cells may disrupt homeostasis in the retinal microenvironment. In this review, the role of altered ECM synthesis, compromised GJ activity, and disturbed retinal homeostasis in the development of retinal vascular lesions in diabetic retinopathy are discussed.

SiRNA strategy against overexpression of extracellular matrix in diabetic retinopathy

Increased synthesis of extracellular matrix (ECM) contributes to the development of vascular BM thickening, a prominent abnormality in diabetic retinopathy. RNA interference (RNAi) approach was used in this study to examine the effect of small interfering RNAs (siRNAs) for their ability to inhibit ECM-specific gene overexpression under high glucose condition in rat microvascular endothelial cells (RMECs). Four fibronectin (FN)-siRNAs, three collagen IV (Coll IV)-siRNAs, and four laminin (LM)-siRNAs, a total of 11 siRNAs were screened. RMECs were transfected with 10, 30, or 100 nm of each siRNAs in the presence of 8 microm lipofectin and subjected to analysis 72 hr after transfection. In long-term studies siRNA-transfected cells were examined after 12 days. Two FN siRNAs, two Coll IV siRNAs, and two LM siRNAs significantly reduced the respective target expressions. Findings from this study indicate that high glucose-induced abnormal expression of BM components may contribute to increased vascular permeability. SiRNA may be a useful tool in preventing excess vascular permeability, a characteristic feature of early diabetic retinopathy.

Expression of placenta growth factor is regulated by both VEGF and hyperglycaemia via VEGFR-2

Placenta growth factor (PlGF) has been implicated in both physiological and pathological angiogenesis; however, little is known about what regulates its expression. In this study, retinal microvascular endothelial cells and pericytes were exposed to varying concentrations of VEGF and glucose and PlGF expression measured by RT-PCR and Western blotting. Both PlGF mRNA and protein were observed in unstimulated microvascular endothelial cells with only weak expression in pericytes. In endothelial cells, VEGF (100 ng/ml) and glucose (15 mM) induced an increase in expression of PlGF at both the mRNA and protein level while no effect was observed for pericytes. The increase in PlGF expression could be totally abolished by blocking VEGFR-2, and in the case of glucose by neutralising VEGF. VEGF-stimulated PlGF expression was largely inhibited by PD 98059, an inhibitor of mitogen-activated protein kinase (MAPK) and partially by GF 109203X, an inhibitor of protein kinase C (PKC), indicating that VEGF up-regulates PlGF expression via the MAPK signalling pathway and partially through PKC. Taken together, our findings suggest that VEGF orchestrates the contribution of PlGF in angiogenesis via more than one intracellular pathway and that hyperglycaemia, as occurs in diabetes, is an important regulator of PlGF expression via VEGF up-regulation.