تم وصف طريقة لتغليف الخلايا الضوئية الشمسية في هيدروجيل PEG crosslinked. يتم تعقب إشارات ميتة داخل ورم جزيري الفئران مغلفة (MIN6) المجاميع باستخدام نظام علامة الفلورسنت. يسمح هذا النظام التسلسلي للفحص الخلايا في غضون سقالة هيدروجيل ويشير ارتباط نقص الأوكسجين مع التغيرات في النمط الظاهري الخلية.
In Diabetes mellitus type 1, autoimmune destruction of the pancreatic β-cells results in loss of insulin production and potentially lethal hyperglycemia. As an alternative treatment option to exogenous insulin injection, transplantation of functional pancreatic tissue has been explored1,2. This approach offers the promise of a more natural, long-term restoration of normoglycemia. Protection of the donor tissue from the host’s immune system is required to prevent rejection and encapsulation is a method used to help achieve this aim.
Biologically-derived materials, such as alginate3 and agarose4, have been the traditional choice for capsule construction but may induce inflammation or fibrotic overgrowth5 which can impede nutrient and oxygen transport. Alternatively, synthetic poly(ethylene glycol) (PEG)-based hydrogels are non-degrading, easily functionalized, available at high purity, have controllable pore size, and are extremely biocompatible,6,7,8. As an additional benefit, PEG hydrogels may be formed rapidly in a simple photo-crosslinking reaction that does not require application of non-physiological temperatures6,7. Such a procedure is described here. In the crosslinking reaction, UV degradation of the photoinitiator, 1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one (Irgacure 2959), produces free radicals which attack the vinyl carbon-carbon double bonds of dimethacrylated PEG (PEGDM) inducing crosslinking at the chain ends. Crosslinking can be achieved within 10 minutes. PEG hydrogels constructed in such a manner have been shown to favorably support cells7,9, and the low photoinitiator concentration and brief exposure to UV irradiation is not detrimental to viability and function of the encapsulated tissue10. While we methacrylate our PEG with the method described below, PEGDM can also be directly purchased from vendors such as Sigma.
An inherent consequence of encapsulation is isolation of the cells from a vascular network. Supply of nutrients, notably oxygen, is therefore reduced and limited by diffusion. This reduced oxygen availability may especially impact β-cells whose insulin secretory function is highly dependent on oxygen11-13. Capsule composition and geometry will also impact diffusion rates and lengths for oxygen. Therefore, we also describe a technique for identifying hypoxic cells within our PEG capsules. Infection of the cells with a recombinant adenovirus allows for a fluorescent signal to be produced when intracellular hypoxia-inducible factor (HIF) pathways are activated14. As HIFs are the primary regulators of the transcriptional response to hypoxia, they represent an ideal target marker for detection of hypoxic signaling15. This approach allows for easy and rapid detection of hypoxic cells. Briefly, the adenovirus has the sequence for a red fluorescent protein (Ds Red DR from Clontech) under the control of a hypoxia-responsive element (HRE) trimer. Stabilization of HIF-1 by low oxygen conditions will drive transcription of the fluorescent protein (Figure 1). Additional details on the construction of this virus have been published previously15. The virus is stored in 10% glycerol at -80° C as many 150 μL aliquots in 1.5 mL centrifuge tubes at a concentration of 3.4 x 1010 pfu/mL.
Previous studies in our lab have shown that MIN6 cells encapsulated as aggregates maintain their viability throughout 4 weeks of culture in 20% oxygen. MIN6 aggregates cultured at 2 or 1% oxygen showed both signs of necrotic cells (still about 85-90% viable) by staining with ethidium bromide as well as morphological changes relative to cells in 20% oxygen. The smooth spherical shape of the aggregates displayed at 20% was lost and aggregates appeared more like disorganized groups of cells. While the low oxygen stress does not cause a pronounced drop in viability, it is clearly impacting MIN6 aggregation and function as measured by glucose-stimulated insulin secretion15. Western blot analysis of encapsulated cells in 20% and 1% oxygen also showed a significant increase in HIF-1α for cells cultured in the low oxygen conditions which correlates with the expression of the DsRed DR protein.
الطريقة المعروضة هنا تقدم تقنية سريعة وبسيطة لتغليف الخلايا في هيدروجيل الربط مع استخدام الحد الأدنى من الشروط غير الفسيولوجية. PEG يمثل مادة التغليف مفيدة جدا للتوافق مع الحياة وسهولة التعديل. اختلاف بسيط من نسبة الربط في حل متفاعل للضوء ، على سبيل المثال ، قد يتم استخدامها لضبط الخواص الميكانيكية ، مثل معامل الضغط ، وخصائص النقل عن طريق حجم المسام. أيضا ، يتم تعديل الربط بسهولة عن طريق إضافة السلاسل الجانبية. PEG الهلاميات المائية ، وبالتالي ، تمثل كل جهاز السريرية واعدة منصة مرنة للأبحاث في المختبر
كما تم تتبع طريقة لنقص الأكسجة في الربط بين الخلايا مغلفة المقدمة. هذه الطريقة مفيدة للكشف عن نقص الأكسجة بساطة وتجنب الحاجة للتضحية خلايا الفائدة. ويمكن تطبيق هذه التقنية لمجموعة متنوعة من أنواع الخلايا في مجموعة متنوعة من الظروف مما يجعلنا فيefulness اسعة. على سبيل المثال ، قد يتم تعقب نقص الأكسجة وتلميحا عن تمايز الخلايا الجذعية في الثقافات الجذعية micromass الخلية. ومع ذلك ، لا يمكن إلا أن تطبق هذه الطريقة لتفريق نظم الخلية أو النظام الذي يتم تجميعها في وقت لاحق فرقت الخلايا. أيضا ، قد كشف للإشارة الفلورسنت يكون من الصعب في الأنسجة أكبر أو أكثر كثافة.
The authors have nothing to disclose.
بفضل المختبر Anseth كريستي من جامعة كولورادو في بولدر لتوريد بسخاء MIN6 الخلايا. وقد تم توفير التمويل لهذا المشروع من قبل جبهة الخلاص الوطني.
Name of the reagent | Company | Catalogue number | Comments (optional |
PEG | Sigma-Aldrich | 309028-500G | |
Methacrylic Anhydride | Sigma-Aldrich | 276685-100ML | |
Microwave | Emerson | MW8784SB | |
Vortexer | Scientific Industries | SI-A236 | |
Methylene Chloride | Sigma-Aldrich | D65100-1L | |
Diethyl Ether | Sigma-Aldrich | 346136-1L | |
Dialysis Tubing | Spectrum | 132640 | |
Laboratories | |||
Freezer | |||
Lyophilizer | Labconco | 7670521 | |
Vacuum pump | Welch | 8917Z-01 | |
Irgacure 2959 | Ciba-Geigy | 029891301PS04 | |
HBSS | Mediatech | 21-022-CV | |
Syringe Filter | VWR | 28145-477 | |
RPMI 1640 | Mediatech | * | *custom formulation |
FBS | PAA Laboratories | A15-351 | |
Penicillin-Streptomycin | Mediatech | 30-002-CI | |
Amphotericin B | Mediatech | 30-003-CF | |
Incubator | Thermo Scientific | 3597 | Napco Series 8000 WJ w/ O2 suppression |
Trypsin EDTA | Mediatech | 25-052-CI | |
Orbital Shaker | VWR | 12620-926 | |
UV Lamp | Sanyo Denri | FLR40SBLB/M | Holds two 40W, 365nm blacklight blue UV bulbs |
Centrifuge | Eppendorf | 5811 000.010* | *order number. Model 5810 R |
Microscope | Nikon | TI-ND6-PFS | With filterset for 556nm excitation/ 586nm emission |