Increased blood glucose concentrations promote reactions between glucose and proteins to form advanced glycation end-products (AGE). Circulating AGE in the blood plasma can activate the receptor for advanced end-products (RAGE), which is present on both endothelial and vascular smooth muscle cells (VSMC). RAGE exhibits a complex signaling that involves small G-proteins and mitogen activated protein kinases (MAPK), which lead to increased nuclear factor kappa B (NF-κB) activity. While RAGE signaling has been previously addressed in endothelial cells, little is known regarding its impact on the function of VSMC. Therefore, we hypothesized that RAGE signaling leads to alterations in the mechanical and functional properties of VSMC, which could contribute to complications associated with diabetes. We demonstrated that RAGE is expressed and functional in the A7r5 VSMC model, and its activation by AGE significantly increased NF-κB activity, which is known to interfere with the contractile phenotype of VSMC. The protein levels of the contraction-related transcription factor myocardin were also decreased by RAGE activation with a concomitant decrease in the mRNA and protein levels of transgelin (SM-22α), a regulator of VSMC contraction. Interestingly, we demonstrated that RAGE activation increased the overall cell rigidity, an effect that can be related to an increase in myosin activity. Finally, although RAGE stimulation amplified calcium signaling and slightly myosin activity in VSMC challenged with vasopressin, their contractile capacity was negatively affected. Overall, RAGE activation in VSMC could represent a keystone in the development of vascular diseases associated with diabetes by interfering with the contractile phenotype of VSMC through the modification of their mechanical and functional properties.

Apoptosis can be routinely characterized using biomolecular markers such as in the TUNEL and the annexin V assays or by using fluorescent caspase substrates. Apoptosis can also be semi-quantitatively characterized using microscopy, which targets morphological features such as cell rounding, nuclear condensation and fragmentation as well as cell membrane blebbing. This label-free approach provides a limited resolution for the evolution of these events in time and relies heavily on subjective identification of the morphological features. Here we propose a label-free assay based on surface plasmon resonance (SPR) detection of minute morphology changes occurring as a result of apoptosis induction in an endothelial cell model (EA.hy926). At first, annexin V assays confirmed that our cellular model was responsive to TRAIL over a 12-hour period. Then, we show that SPR allows accurate monitoring of apoptosis by measuring (1) the duration of the latency period during which the apoptotic signal is integrated by the initiator caspases and transmitted to the executioner caspases, (2) the rate of the execution phase in which death substrates are cleaved and morphological changes occur, and (3) the total extent of apoptosis. Using these parameters, we characterized the responses obtained with TRAIL (EA.hy926, HeLa, AD-293) and the anti-Fas antibody (HeLa) for the extrinsic pathways and UV exposure (HeLa) for the intrinsic pathways. By comparing the SPR time-course of apoptosis with phase contrast micrographs, we demonstrate that the cell morphological hallmarks of apoptosis are the major contributors to the SPR signal. Altogether, our results validate the use of SPR as an accurate label-free assay for the real-time monitoring of apoptosis-triggered cell morphological changes.

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