Collagen type VI interaction improves human islet survival in immunoisolating microcapsules for treatment of diabetes

Abstract

Collagens are the most abundant fibrous protein in the human body and constitute the main structural element of the extracellular matrix. It provides mechanical and physiological support for cells. In the pancreas, collagen VI content is more than double that of collagen I or IV. It is a major component of the islet-exocrine interface and could be involved in islet-cell survival. To test the impact of collagen VI on human encapsulated pancreatic islets-cells, we tested the effects of exogenous collagen type VI on in vitro functional survival of alginate encapsulated human islet-cells. Concentrations tested ranged from 0.1 to 50 µg/ml. Islets in capsules without collagen type VI served as control. Islet-cell interaction with collagen type VI at concentrations of 0.1 and 10 µg/ml, promoted islet-cell viability (p<0.05). Although no improvement in glucose induced insulin secretion (GSIS) was observed, islets in capsules without incorporation of collagen type VI showed more dysfunction and oxygen consumption rates was improved by inclusion of collagen type VI. Our results demonstrate that incorporation of collagen type VI in immunoisolated human islets supports in vitro viability and survival of human pancreatic islets.

Keywords: alginate capsules; collagen; glucose induced insulin secretion; oxygen consumption rate; pancreatic islets; viability.

Figure 1.

Glucose induced insulin secretion (GSIS) of human islets encapsulated in alginate-based capsules supplemented with collagen VI. Concentrations of 0.1, 10 and 50 µg/ml collagen VI tested at day 3 (a), 5 (b) and 7 (c). The bars from left to right indicate insulin production upon incubation with low (2.75 mM), high (16.7 mM), and low glucose solution of sets of 25 pancreatic human islets for each condition. Values represent mean ± SEM (n = 4, different donors).

Figure 2.

The figure shows the stimulation index (SI) of encapsulated islet in response to low (2.75 mM), and high (16.7 mM) glucose. Results from human islets encapsulated in alginate-based capsules supplemented with collagen VI at concentrations of 0.1, 10 and 50 µg/ml collagen VI tested at day 3, 5 and 7. Error bars represent standard error. Statistical significance is indicated by stars (p < 0.05).

Figure 3.

Live/dead staining of human islet-cells encapsulated in alginate-based capsules containing either 0.1, 10, and 50 µg/ml collagen type VI. Illustration of islets in control condition (in alginate capsule without collagen), and a capsule containing 10 µg/ml collagen VI (a). Islet-cell viability was enhanced by inclusion of collagen VI in the immunoprotective capsule at all-time points tested (b). Encapsulated human islets were stained with ethidium homodimer-1 to quantify the percentage of dead cells at days 3, 5, and 7 of culture (c). Alginate capsules without ECM components served as control. Values represent mean ± SEM (n = 4, different donors). *, and ** indicates statistical significant differences (p < 0.05), and (p < 0.01) when compared to control islets respectively (Col VI, collagen type VI).

Figure 4.

Oxygen consumption rate (OCR) of human islets encapsulated in alginate capsules containing a combination of 0.1, 10 or 50 µg/ml after 72 hours in culture. OCR was expressed after correction for DNA content (OCR/DNA). Values represent mean ± SEM. *, and ** indicates statistical significant differences (p < 0.05), and (p < 0.01) when compared to control islets respectively (n = 4, different donors).