Dan Luciani

 
Prospective Graduate Students / Postdocs

This faculty member is currently not looking for graduate students or Postdoctoral Fellows. Please do not contact the faculty member with any such requests.

Associate Professor

Research Classification

Diabetes

Research Interests

Diabetes
Pancreatic beta-cell function and failure
Mitochondrial physiology
Cell calcium signalling
Cell stress signalling
Mechanisms of cell death
autophagy

Relevant Degree Programs

 

Research Methodology

Live-cell Confocal Microscopy
High Content Imaging
Cellular Bioenergetic Analysis (Seahorse XFe96 System)

Graduate Student Supervision

Master's Student Supervision (2010-2017)
Bcl-xL protects pancreatic beta-cells from high glucose-induced failure by dampening mitochondrial metabolism (2015)

Chronic nutrient oversupply, such as seen in obesity, increases metabolic load and oxidative stress in the insulin-secreting β-cells. This progressively impairs β-cell function and survival, contributing to the development of type 2 diabetes. Bcl-xL is an antiapoptotic protein of the Bcl-2 family. Recent studies have shown additional non-apoptotic functions of Bcl-xL in suppressing glucose signaling of non-diabetic β-cells. Conceivably, this metabolic dampening may be beneficial to counter β-cell dysfunction during nutrient excess of type 2 diabetes. To test the hypothesis that Bcl-xL protects β-cell function during metabolic stress via regulation of mitochondrial physiology, we examined the effects of gene deletion and overexpression of Bcl-xL in β-cells. In normal conditions, islets of β-cell-specific Bcl-x knockout (BclxβKO) mice tend to be metabolically more active compared to BclxβWT islets. This metabolic effect of Bcl-xL is further enhanced after prolonged high glucose culture, where BclxβKO islets display a pre-toxic state of metabolic amplification with dysregulated intracellular Ca²+ and insulin secretion. Islets overexpressing Bcl-xL display suppressed intracellular Ca²+ responses, in agreement with our knockout studies. Interestingly, cells expressing Bcl-xL at high levels have increased mitochondrial aggregates. We also demonstrated that Bcl-xL suppresses superoxide levels and cell death induced by ribose, but not islet-cell death under glucolipotoxic conditions. In conclusion, we propose that endogenous Bcl-xL protects β-cells from high glucose-induced failure by dampening mitochondrial activity, as well as suppressing oxidative stress-induced cell death.

View record

Novel functions of B7-H4 in β cell physiology and stress response (2015)

Stress-induced failure and death of pancreatic β-cells are integral steps in the pathogenesis of type 1 and type 2 diabetes. Better understanding of the molecular interactions that influence β-cell function and stress signaling may therefore identify therapeutic targets to protect endogenous β-cells or transplanted islet grafts. B7-H4 is a negative co-stimulatory molecule that is expressed on the cell membranes of antigen presenting cells and down-regulates the immune response. Interestingly, pancreatic β-cells also express high levels of B7-H4 mRNA and moderate levels of B7-H4 protein. Of note, various tumor cells have up-regulated levels of B7-H4, which has been linked to metabolic and anti-apoptotic effects. This raises the intriguing possibility that B7-H4 may also regulate β-cell function, stress signaling, and survival independent of immune-regulation. In this study, we used mice with β-cell-specific overexpression of B7-H4, as well as B7-H4 knockout mice to examine the possible roles of B7-H4 in β-cell physiology and responses to endoplasmic reticulum (ER) stress. Cytosolic Ca²+ imaging showed that B7-H4 transgenic islets had increased sensitivity to sub-maximal glucose stimulation. Additional experiments indicated no differences in ER Ca²+ uptake/release or glucose metabolism, but revealed that B7-H4 transgenic islets are sensitized to tolbutamide and are resistant to diazoxide, suggesting changes at the ATP-sensitive potassium channels. The B7-H4-induced amplification of glucose-stimulated Ca²+ did not translate into detectable differences in in vitro insulin secretion or in vivo glucose tolerance, suggesting secondary control between rise in intracellular calcium and exocytosis of insulin granules. ER stress was induced in vitro using thapsigargin, and gene expressions were compared by real time quantitative PCR. Moderate ER stress induced the expression of key unfolded protein response genes, BiP, CHOP, and XBP1s to significantly higher levels in B7-H4 transgenic islets compared with wild type. However, the death of dispersed B7-H4 and wild type islet-cells did not differ following more severe and prolonged ER stress. Together, our findings demonstrate that over-expression of B7-H4 amplifies β-cell glucose-stimulated Ca²+ responses and the unfolded protein response during ER stress, revealing novel roles for B7-H4 in the pancreatic β-cell.

View record

Pro-apoptotic bax and bak control beta-cell death and early endoplasmic reticulum stress signalling (2013)

Functional failure and loss of pancreatic β-cells are critical events in the pathogenesis of diabetes and there is mounting evidence that suggests chronic endoplasmic reticulum (ER) stress contributes significantly to β-cell dysfunction and apoptotic death. Two core pro-apoptosis proteins, Bax and Bak, mediate the execution of mitochondrial apoptosis and have also been suggested to regulate aspects of ER physiology and stress signalling. In this study we set out to determine the relative contributions of Bax and Bak in the execution of β-cell death and examine their putative roles in β-cell ER-stress signalling under diabetogenic conditions. We generated mice in which the single or combined knockout of Bax and Bak could be induced in the pancreatic β-cell. Physiological islet function assessed both in vivo and in vitro was not affected by the knockout of Bax and/or Bak. However, Bax and Bak knockout improved β-cell survival under stress conditions. Single knockout, double knockout, and wild-type cells were assayed for ER-stress and cell death following treatment with staurosporine, thapsigargin, and culture under glucolipotoxic conditions. Time-course kinetic cell death analysis demonstrated that single and double knockout cells were protected from staurosporine, and further revealed that Bax-Bak double knockout was required for significant protection from death under glucolipotoxic conditions. ER-stress signalling was evaluated by quantitative PCR for XBP1s and CHOP. Interestingly, spliced XBP1 expression was augmented in Bax-Bak double knockout islets in the early phase of ER-stress signalling compared to wild-type controls. Stress-induced CHOP expression increased in a time-dependent manner but was not significantly different between Bax-Bak double knockout and wild-type islets. These results suggest that Bax and Bak regulate the IRE1α arm of the ER-stress response upstream of apoptosis by suppressing maximal XBP1 splicing. Under glucolipotoxic conditions, pancreatic insulin content, insulin secretion, and insulin transcription were unaffected by Bax and Bak knockout, indicating Bax and Bak do not mediate their protective effects towards β-cell death by retaining islet function. Together these data demonstrate that Bax and Bak have both individual and combined contributions to β-cell death under various stress conditions and suggest novel non-apoptotic roles regulating early ER-stress signalling in the β-cell.

View record

Publications

 

Membership Status

Member of G+PS

Location

BC Children's Hospital

Department(s)

 

If this is your researcher profile you can log in to the Faculty & Staff portal to update your details and provide recruitment preferences.