(A-18) Influence of the Biomechanical Environment on β-cell Function and Maturity

Introduction:: It is well-established that cells respond to mechanical cues via cytoskeletal remodeling. However, it is not known whether the mechanical environment influences β-cell maturity and function. The coordination between β-cells, and potentially between other endocrine cells, is necessary for proper oscillatory insulin release in the presence of elevated glucose. Here we examine how mechanical stimuli impact coordinated β-cell Ca²⁺ oscillatory dynamics and expression of β-cell maturity markers.


Materials and Methods:: To examine how mechanical cues influence the β-cell, we used biocompatible substrates with tunable mechanical properties synthesized with elastic moduli ranging from ~3kPa–33 kPa (Fig.1A). The surface was coated with extracellular matrix and MIN6 β-like cells were seeded. To independently examine a link between β-cell function and maturity, we examined islet cells from mice in which β-cells express CaMPARI, a photoconvertible fluorescent protein that in the presence of high Ca²⁺ activity changes from green to red. The CaMPARI islets were gently dissociated, and individual islet cells were seeded atop substrates with varied stiffness. For all conditions in MIN6 cells and CAMPARI-expressing dissociated islets, we imaged Ca²⁺ dynamics via Fluo4 at low (2mM) and high glucose (11, 20mM). qPCR was conducted on MIN6 cells (6, 22 kPa) to examine expression of genes linked to β-cell function and maturity.

Results, Conclusions, and Discussions:: Results and Discussion: With increased substrate stiffness, MIN6 cell Ca²⁺ oscillations were more robust, including a significant increase in duty cycle (p < 0.01) and were more coordinated, consistent with increased excitability (Fig. 1B-D). With increasing stiffness, there was significantly decreased expression of Sur1, Kir6.2, Ins2, Pdx1, Fltp, and Ecad (Fig. 1D, p < 0.01). Thus, the dynamics and coordination of Ca²⁺ activity is mechanoresponsive and may result from altered β-cell maturity. In CaMPARI islets, Ca²⁺ oscillations were more robust and coordinated for photo-converted red cells which marks cells with higher Ca²⁺, compared to green cells (Fig.1F). With increased substrate stiffness, the fraction of these red cells that exhibit higher Ca²⁺ was increased, again showing that stiffness influences β-cell excitability. Taken together, we show evidence in both MIN6 cells and isolated primary β-cells that with increased substrate stiffness cells are more excitable and may have altered maturity.

Conclusions: In conclusion, our results suggest there may be an inverse relationship between β-cell maturity and function. Further, that the maturity and function of β-cells is responsive to the mechanical environment.


Acknowledgements (Optional): : Funding was provided by: BDC ACORN post-doctoral fellowship (KV) and NIH/NDDK grants –# R01 DK102950 and R01 DK106412 (RB). Additionally, we thank the BDC islet core for assistance with pancreas isolation.


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