Superoxide dismutase reduces islet microvascular injury induced by streptozotocin in the rat

Danggui Sini Decoction Protected Islet Endothelial Cell Survival from Hypoxic Damage via PI3K/Akt/eNOS Pathway

Danggui Sini decoction (DSD) is a traditional Chinese decoction, which is wildly applied and showed to be effective in ameliorating ischemia-related symptoms. However, the mechanisms of DSD action in ischemic damage remain to be fully clarified. Pancreatic islet endothelial cells are pivotal constituent of islet microvasculature, with high vulnerability to hypoxic injuries. Here, using MST1 cell, a pancreatic islet endothelial cell-line, as a model, we investigated the effects of DSD on hypoxia-stimulated endothelial cell lesions and its underlying mechanisms. We found that DSD-Containing Serum (DSD-CS), collected from DSD-treated rats, could efficiently protect MST1 survival and proliferation from Cobalt chloride (CoCl₂) induced damage, including cell viability, proliferation, and tube formation. Furthermore, DSD-CS restored the activity of PI3K/Akt/eNOS signaling inhibited by CoCl₂ in MST1 cells. The protective effect of DSD-CS could be blocked by the specific PI3K/Akt/eNOS inhibitor LY294002, suggesting that DSD-CS protection of MST1 cell survival from hypoxia was mediated by PI3K/Akt/eNOS pathway. In conclusion, DSD treatment protected MST1 survival from hypoxic injuries via PI3K/Akt/eNOS pathway, indicating its role in protecting microvascular endothelial cells.

Plasticity of Schwann cells and pericytes in response to islet injury in mice

AIMS/HYPOTHESIS

Islet Schwann (glial) cells and pericytes are the microorgan's accessory cells positioned at the external and internal boundaries facing the exocrine pancreas and endothelium, respectively, adjacent to the endocrine cells. Plasticity of glial cells and pericytes is shown in the glial scar formation after injury to the central nervous system. It remains unclear whether similar reactive cellular responses occur in insulitis. We applied three-dimensional (3D) histology to perform qualitative and quantitative analyses of the islet Schwann cell network and pericytes in normal, streptozotocin-injected (positive control of gliosis) and NOD mouse models.

METHODS

Vessel painting paired with immunostaining of mouse pancreatic tissue was used to reveal the islet Schwann cells and pericytes and their association with vasculature. Transparent islet specimens were prepared by optical clearing to facilitate 3D confocal microscopy for panoramic visualisation of the tissue networks.

RESULTS

In-depth microscopy showed that the islet Schwann cell network extends from the peri-islet domain into the core. One week after streptozotocin injection, we observed intra-islet perivascular gliosis and an increase in pericyte density. In early/moderate insulitis in the NOD mice, perilesional gliosis occurred at the front of the lymphocytic infiltration with atypical islet Schwann cell morphologies, including excessive branching and perivascular gliosis. Meanwhile, pericytes aggregated on the walls of the feeding arteriole at the peri- and intralesional domains with a marked increase in surface marker density.

CONCLUSIONS/INTERPRETATION

The reactive cellular responses demonstrate plasticity and suggest a stop-gap mechanism consisting of the Schwann cells and pericytes in association with the islet lesion and vasculature when injury occurs.

3-D imaging and illustration of the perfusive mouse islet sympathetic innervation and its remodelling in injury

AIMS/HYPOTHESIS

Sympathetic nerves influence islet hormone levels in the circulation. Insights into islet sympathetic innervation and its remodelling in diabetes may impact future therapeutics. However, standard immunohistochemistry and microtome-based microscopy cannot provide an integral view of the islet neurovascular complex. We prepared transparent islet specimens to investigate the spatial relationship between sympathetic nerves, blood vessels and islet cells in normal, streptozotocin-injected and non-obese diabetic mouse models.

METHODS

Cardiac perfusion of fluorescent lectin was used to label pancreatic blood vessels. Tyrosine hydroxylase and nuclear staining were used to reveal islet sympathetic innervation and microstructure. Optical clearing (i.e. use of immersion solution to reduce scattering) was applied to enable 3-dimensional confocal microscopy of islets to visualise the sympathetic neurovascular complex in space.

RESULTS

Unlike previously reported morphology, we observed perfusive intra-islet, perivascular sympathetic innervation, in addition to peri-islet contacts of sympathetic nerves with alpha cells and sympathetic fibres encircling the adjacent arterioles. The intra-islet axons became markedly prominent in streptozotocin-injected mice (2 weeks after injection). In non-obese diabetic mice, lymphocytic infiltration remodelled the peri-islet sympathetic axons in early insulitis.

CONCLUSIONS/INTERPRETATION

We have established an imaging approach to reveal the spatial features of mouse islet sympathetic innervation. The neurovascular complex and sympathetic nerve-alpha cell contact suggest that sympathetic nerves modulate islet hormone secretion through blood vessels, in addition to acting directly on alpha cells. In islet injuries, sympathetic nerves undergo different remodelling in response to different pathophysiological cues.

Molecular mechanisms of tungstate-induced pancreatic plasticity: a transcriptomics approach

Background

Sodium tungstate is known to be an effective anti-diabetic agent, able to increase beta cell mass in animal models of diabetes, although the molecular mechanisms of this treatment and the genes that control pancreas plasticity are yet to be identified. Using a transcriptomics approach, the aim of the study is to unravel the molecular mechanisms which participate in the recovery of exocrine and endocrine function of streptozotocin (STZ) diabetic rats treated with tungstate, determining the hyperglycemia contribution and the direct effect of tungstate.

Results

Streptozotocin (STZ)-diabetic rats were treated orally with tungstate for five weeks. Treated (STZ)-diabetic rats showed a partial recovery of exocrine and endocrine function, with lower glycemia, increased insulinemia and amylasemia, and increased beta cell mass achieved by reducing beta cell apoptosis and raising beta cell proliferation. The microarray analysis of the pancreases led to the identification of three groups of differentially expressed genes: genes altered due to diabetes, genes restored by the treatment, and genes specifically induced by tungstate in the diabetic animals. The results were corroborated by quantitative PCR. A detailed description of the pathways involved in the pancreatic effects of tungstate is provided in this paper. Hyperglycemia contribution was studied in STZ-diabetic rats treated with phloridzin, and the direct effect of tungstate was determined in INS-1E cells treated with tungstate or serum from untreated or treated STZ-rats, observing that tungstate action in the pancreas takes places via hyperglycemia-independent pathways and via a combination of tungstate direct and indirect (through the serum profile modification) effects. Finally, the MAPK pathway was evaluated, observing that it has a key role in the tungstate-induced increase of beta cell proliferation as tungstate activates the mitogen-activated protein kinase (MAPK) pathway directly by increasing p42/p44 phosphorylation and indirectly by decreasing the expression of raf kinase inhibitor protein (Rkip), a negative modulator of the pathway.

Conclusion

In conclusion, tungstate improves pancreatic function through a combination of hyperglycemia-independent pathways and through its own direct and indirect effects, whereas the MAPK pathway has a key role in the tungstate-induced increase of beta cell proliferation.

Noninvasive magnetic resonance imaging of microvascular changes in type 1 diabetes

OBJECTIVE

The pathogenesis of type 1 diabetes involves autoimmune lymphocytic destruction of insulin-producing beta-cells and metabolic dysregulation. An early biomarker of pancreatic islet damage is islet microvascular dysfunction, and alterations in vascular volume, flow, and permeability have been reported in numerous models of type 1 diabetes. Consequently, the ability to noninvasively monitor the dynamics of the pancreatic microvasculature would aid in early diagnosis and permit the assessment, design, and optimization of individualized therapeutic intervention strategies.

RESEARCH DESIGN AND METHODS

Here, we used the long circulating paramagnetic contrast agent, protected graft copolymer (PGC) covalently linked to gadolinium-diethylenetriaminepentaacetic acid residues (GdDTPAs) labeled with fluorescein isothiocyanate (PGC-GdDTPA-F), for the noninvasive semiquantitative evaluation of vascular changes in a streptozotocin (STZ)-induced mouse model of type 1 diabetes. Diabetic animals and nondiabetic controls were monitored by magnetic resonance imaging (MRI) after injection of PGC-GdDTPA-F.

RESULTS

Our findings demonstrated a significantly greater accumulation of PGC-GdDTPA-F in the pancreata of diabetic animals compared with controls. MRI permitted the in vivo semiquantitative assessment and direct visualization of the differential distribution of PGC-GdDTPA-F in diabetic and control pancreata. Ex vivo histology revealed extensive distribution of PGC-GdDTPA-F within the vascular compartment of the pancreas, as well as considerable leakage of the probe into the islet interstitium. By contrast, in nondiabetic controls, PGC-GdDTPA-F was largely restricted to the pancreatic vasculature at the islet periphery.

CONCLUSIONS

Based on these observations, we conclude that in the STZ model of type 1 diabetes, changes in vascular volume and permeability associated with early stages of the disease can be monitored noninvasively and semiquantitatively by MRI.