Enhanced expression of β cell Ca _V 3.1 channels impairs insulin release and glucose homeostasis

Abstract

Voltage-gated calcium 3.1 (CaV3.1) channels are absent in healthy mouse β cells and mediate minor T-type Ca2+currents in healthy rat and human β cells but become evident under diabetic conditions. Whether more active CaV3.1 channels affect insulin secretion and glucose homeostasis remains enigmatic. We addressed this question by enhancing de novo expression of β cell CaV3.1 channels and exploring the consequent impacts on dynamic insulin secretion and glucose homeostasis as well as underlying molecular mechanisms with a series of in vitro and in vivo approaches. We now demonstrate that a recombinant adenovirus encoding enhanced green fluorescent protein–CaV3.1 subunit (Ad-EGFP-CaV3.1) efficiently transduced rat and human islets as well as dispersed islet cells. The resulting CaV3.1 channels conducted typical T-type Ca2+currents, leading to an enhanced basal cytosolic-free Ca2+concentration ([Ca2+]i). Ad-EGFP-CaV3.1-transduced islets released significantly less insulin under both the basal and first phases following glucose stimulation and could no longer normalize hyperglycemia in recipient rats rendered diabetic by streptozotocin treatment. Furthermore, Ad-EGFP-CaV3.1 transduction reduced phosphorylated FoxO1 in the cytoplasm of INS-1E cells, elevated FoxO1 nuclear retention, and decreased syntaxin 1A, SNAP-25, and synaptotagmin III. These effects were prevented by inhibiting CaV3.1 channels or the Ca2+-dependent phosphatase calcineurin. Enhanced expression of β cell CaV3.1 channels therefore impairs insulin release and glucose homeostasis by means of initial excessive Ca2+influx, subsequent activation of calcineurin, consequent dephosphorylation and nuclear retention of FoxO1, and eventual FoxO1-mediated down-regulation of β cell exocytotic proteins. The present work thus suggests an elevated expression of CaV3.1 channels plays a significant role in diabetes pathogenesis.

Glucose-induced insulin secretion in isolated human islets: Does it truly reflect β-cell function in vivo?

“…During stimulation with either G10 or G15 ( Figure 2 A), insulin secretion was ∼1.9-fold higher at the peak of the first phase than during the plateau of the second phase, a ratio that is consistent between laboratories ( Table 1 ). Provided the sampling rate is high enough (fractions collected every minute or less), the ratio ranges between 1.4 and 2.2 for stimulations from G3 to G10-G11 [ 37 , 43 , 68 , 69 ], and between 1.3 and 2.5 for stimulations from G3 to G15-G17 [ 37 , [69] , [70] , [71] , [72] , [73] , [74] ]. The two phases are less readily distinguished when sampling rates are lower [ 22 , [75] , [76] , [77] , [78] , [79] , [80] , [81] , [82] , [83] ] ( Table 1 ).…”

Intracameral Microimaging of Maturation of Human iPSC Derivatives into Islet Endocrine Cells

“…Recipient mice were individually subjected to induction of general anesthesia in a veterinary anesthesia induction chamber containing isoflurane followed by inhalation of a mixture of 2.5% isoflurane and 40% oxygen via a nose mask. The head and eyeball of anesthetized mice were immobilized with a head holder and stabilized with an eyeball holder, respectively, for transplantation surgery 23 . Next, hiPSC-SIs are gently aspirated into a glass micropipette, referred to as donor tissue-delivering microcannula, connected by tygon tubing to a threaded plunger syringe.…”

“…Subsequently, a long-distance water-dipping lenses (Leica HXC APO L10×/0.3 W U-V-I) was immersed into Viscotears on the cornea and focused on a hiPSC-SI of interest. The backscattering signal was registered when 633 nm laser light was used to illuminate the ACE and the detection wavelength of reflected light was set at 630-640 nm 23 . For visualization of vasculatures in hiPSC-SI grafts and their attached iris, recipient mice received injection of 0.4 μmol/L Qtracker 565 (Life Technologies, Carlsbad, CA, USA) in 100 µL saline into the tail vein.…”

Abnormal Serum Levels of Autoantibodies to Neural Tissue Antigens in Patients with Schizoaffective Psychosis: Relationship with Herpes Viruses

“…Повышение уровня ауто-АТ к вольтаж-зависимому кальциевому каналу (VGCC) (идентифицирован в мембране нейронов, эндокринных и мышечных клеток) установлено у 11,5% больных основной и у 3% лиц контрольной группы. Аномалии содержания ауто-АТ к антигенам VGCC могут указывать на широкий спектр расстройств с нарушениями водно-электро литного баланса и энергетического метаболизма нейронов, на изменение соотношений между возбуждающими и тормозными процессами в нервной системе, на нарушение функций межнейронных и нервно-мышечных контактов [12] и эндокринный дисбаланс [13], а также на вовлечение в патологические процессы спинного мозга и мозжечка [14].…”