89 research outputs found
A multifactorial approach to targeting signalling pathways in diabetic foot ulcers
Diabetic foot ulcers (DFU) are one of the most debilitating complication of diabetes that
adversely impacts the health, economics and quality of life of the afflicted individual.
The primary pathogenic factor of DFU is hyperglycemia, and its negative effects on
normal signaling pathways is still being investigated. As such, there is no specific
therapy that could target the underlying dysregulations caused by hyperglycemia. So,
it is important to delve into various pathways that are altered by hyperglycemia in
diabetic foot in order to successfully establish novel treatment paradigms.
Wound healing consists of various phases where different cellular processes such as
cell proliferation, migration, angiogenesis and apoptosis coordinate to achieve a swift
healing of the wound. In my thesis, I have investigated several signaling pathways
that play key roles in wound healing and are profoundly disturbed by hyperglycemia
in diabetes.
Notch signaling pathway is an important pathway where receptors and ligands from
juxtaposed cells activate signal transduction. Upon activation, an intracellular domain
of Notch (NICD) translocates to the nucleus and initiates the transcription of specific
targets to control cell proliferation, cell migration, angiogenesis, differentiation and
apoptosis. In paper-I, we show that Notch1 is activated in human and rodent skin and
several processes central to wound healing are impaired in response to hyperglycemia
in a Notch1 dependent manner. Mechanistically, we show that hyperglycemia activates
a Dll4-Notch1 feedforward loop that impairs wound healing in diabetes. Inhibition
of Notch signaling by chemical and genetic approaches improved wound healing in
diabetic mice significantly.
IGF-I is a growth hormone that is expressed in every cell of our body. The circulating
IGF-I is however derived mainly from the liver. IGF-I promotes wound healing and
its levels are decreased in diabetic wounds. However, the contribution of circulating
IGF-I to wound healing is unknown. In Paper II, we generated a liver-specific IGF-I
knockout mice and induced diabetes in these mice to study the effect of liver-derived
IGF-I on wound healing. We found that the lack of liver-derived IGF-I did not affect
healthy wound healing. Although diabetes
delayed wound healing, there was no difference
between knock-out mice and control mice. In addition, the processes contributing
to wound healing were not altered by the liver-derived IGF-I deficiency. In
summary, we found that a lack of liver-derived IGF-I did not affect wound healing.
Future therapies using IGF-I can be designed to be delivered locally since systemic
IGF-I therapy is known to carry risks of unfavorable side-effects.
In papers-III and IV, I have investigated the roles of miRNA-210 and miRNA-34a
in diabetic wound healing respectively. miR-210 is induced by transcription factor
HIF-1 in response to hypoxia. miR-210 mirrors HIF function in hypoxia by regulating
important processes such as cell proliferation, migration, apoptosis, metabolism and angiogenesis. We found that miR-210 expression is reduced in diabetic wounds
and locally reconstituting miR-210 using mimics improves diabetic wound healing
significantly. miR-210 reconstitution led to a reduction in the oxygen consumption rate
in the wounds that led to a decrease in ROS levels in the wound tissue. This metabolic
reprogramming by miR-210 ultimately resulted in the improvement in different cellular
processes central to wound healing.
miR-34a plays important roles in cell cycle and DNA repair. Importantly, miR-34a
has been shown to regulate Notch1 directly. Although there are contrasting reports
on their function in hypoxia and diabetes, their role in diabetic wound healing has not
been elucidated. In paper-IV, we show that miR-34a was reduced in DFUs and in the
wounds of diabetic mice. We also found that a long exposure to hypoxia increased
miR-34a expression exclusively in keratinocytes but exposing cells to high glucose
decreased its expression in hypoxia. Reciprocally, Notch1 expression levels increased
in keratinocytes under hypoxic and high glucose levels in a time-dependent manner.
Finally, we found that diabetic wounds injected with miR-34a mimic showed significantly
lower expression of Notch1, directly correlating with paper-I, indicating that
reconstitution of miR-34a could be a potential therapeutic strategy for diabetic wounds
Repression of hypoxia-inducible factor-1 contributes to increased mitochondrial reactive oxygen species production in diabetes
Background: Excessive production of mitochondrial reactive oxygen species (ROS) is a central mechanism for the development of diabetes complications. Recently, hypoxia has been identified to play an additional pathogenic role in diabetes. In this study, we hypothesized that ROS overproduction was secondary to the impaired responses to hypoxia due to the inhibition of hypoxia-inducible factor-1 (HIF-1) by hyperglycemia. Methods: The ROS levels were analyzed in the blood of healthy subjects and individuals with type 1 diabetes after exposure to hypoxia. The relation between HIF-1, glucose levels, ROS production and its functional consequences were analyzed in renal mIMCD-3 cells and in kidneys of mouse models of diabetes. Results: Exposure to hypoxia increased circulating ROS in subjects with diabetes, but not in subjects without diabetes. High glucose concentrations repressed HIF-1 both in hypoxic cells and in kidneys of animals with diabetes, through a HIF prolyl-hydroxylase (PHD)-dependent mechanism. The impaired HIF-1 signaling contributed to excess production of mitochondrial ROS through increased mitochondrial respiration that was mediated by Pyruvate dehydrogenase kinase 1 (PDK1). The restoration of HIF-1 function attenuated ROS overproduction despite persistent hyperglycemia, and conferred protection against apoptosis and renal injury in diabetes. Conclusions: We conclude that the repression of HIF-1 plays a central role in mitochondrial ROS overproduction in diabetes and is a potential therapeutic target for diabetic complications. These findings are timely since the first PHD inhibitor that can activate HIF-1 has been newly approved for clinical use. Funding: This work was supported by grants from the Swedish Research Council, Stockholm County Research Council, Stockholm Regional Research Foundation, Bert von Kantzows Foundation, Swedish Society of Medicine, Kung Gustaf V:s och Drottning Victorias Frimurarestifelse, Karolinska Institute's Research Foundations, Strategic Research Programme in Diabetes, and Erling-Persson Family Foundation for S-B.C.; grants from the Swedish Research Council and Swedish Heart and Lung Foundation for T.A.S.; and ERC consolidator grant for M.M.Peer reviewe
Epigenetic Regulation of Virulence Gene Expression in Parasitic Protozoa
Protozoan parasites colonize numerous metazoan hosts and insect vectors through their life cycles, with the need to respond quickly and reversibly while encountering diverse and often hostile ecological niches. To succeed, parasites must also persist within individuals until transmission between hosts is achieved. Several parasitic protozoa cause a huge burden of disease in humans and livestock, and here we focus on the parasites that cause malaria and African trypanosomiasis. Efforts to understand how these pathogens adapt to survive in varied host environments, cause disease, and transmit between hosts have revealed a wealth of epigenetic phenomena. Epigenetic switching mechanisms appear to be ideally suited for the regulation of clonal antigenic variation underlying successful parasitism. We review the molecular players and complex mechanistic layers that mediate the epigenetic regulation of virulence gene expression. Understanding epigenetic processes will aid the development of antiparasitic therapeutics
Optical molecular imaging of lysyl oxidase activity â detection of active fibrogenesis in human lung tissue
Biochemistry of periodontal connective tissues and their regeneration: A current perspective
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