Beta cell mass and growth after syngeneic islet cell transplantation in normal and streptozocin diabetic C57BL/6 mice

In islet transplantation, nonimmunological factors such as limited growth capacity or increased death rate could reduce the beta cell mass in the graft and lead to failure of the transplant. We studied the evolution of beta cell replication and mass after transplantation of insufficient, minimally sufficient, or excessive islet tissue. Streptozocin diabetic C57BL/6 mice received 150 or 300 syngeneic islets under the kidney capsule and normal mice received 300 islets. In streptozocin diabetic mice 300 islets restored normoglycemia; beta cell replication in transplanted islets was similar to replication in normal pancreas and beta cell mass in the graft remained constant. In contrast, 150 islets were insufficient to achieve normoglycemia; beta cell replication was increased initially but not by 18 or 30 d despite persistent hyperglycemia, and beta cell mass fell progressively. When islets were transplanted into normal recipients, beta cell replication remained normal but beta cells underwent atrophy and mass in the graft was substantially reduced. Therefore, with a successful islet transplant, in diabetic mice beta cell replication and mass remain constant. In contrast, when insufficient islet tissue is transplanted an initial increase in beta cell replication can not compensate for a decline in beta cell mass. When excessive islet tissue is transplanted, beta cell mass is reduced despite normal beta cell replication.

Transplanted beta cell response to increased metabolic demand. Changes in beta cell replication and mass

We determined the capacity of transplanted beta cells to modify their replication and mass when stimulated by changes in metabolic demand. Five groups of Lewis rats were studied: group 1 (Tx-Px) had a 95% pancreatectomy 14 d after transplantation of 500 islets; group 2 (Px-Tx) had a 95% pancreatectomy 14 d before transplantation of 500 islets; group 3 (Tx) was transplanted with 500 islets; group 4 (Px) had a 95% pancreatectomy; and group 5 (normal) was neither transplanted nor pancreatectomized. Blood glucose was normal in Tx-Px and Tx groups at all times. Px-Tx and Px groups developed severe hyperglycemia after pancreatectomy that was corrected in Px-Tx group in 83% of rats 28 d after transplantation. Replication of transplanted beta cells increased in Tx-Px (1.15 +/- 0.12%) and Px-Tx (0.85 +/- 0.12%) groups, but not in Tx group (0.64 +/- 0.07%) compared with normal pancreatic beta cells (0.38 +/- 0.05%) (P < 0.001). Mean beta cell size increased in Tx-Px (311 +/- 14 microns2) and Px-Tx (328 +/- 13 microns2) groups compared with Tx (252 +/- 12 microns2) and normal (239 +/- 9 microns2) groups (P < 0.001). Transplanted beta cell mass increased in Tx-Px (1.87 +/- 0.51 mg) and Px-Tx (1.55 +/- 0.21 mg) groups compared with Tx group (0.78 +/- 0.17 mg) (P < 0.05). In summary, changes in transplanted beta cells prevented the development of hyperglycemia in Tx-Px rats. Transplanted beta cells responded to increased metabolic demand increasing their beta cell mass.

Ultrastructural characterisation of the cell wall of Arabidopsis thaliana transgenic plants

The plant cell wall is a strong fibrillar network that gives each cell its stable shape. It is constituted by a network of cellulose microfibrils embedded in a matrix of polysaccharides, such as xyloglucans. To enlarge, cells selectively loosen this network. Moreover, there is a pectin-rich intercellular material, the middle lamella, cementing together the walls of adjacent plant cells. Xyloglucan endotransglucosylase/hydrolases (XTHs) are a group of enzymes involved in the reorganisation of the cellulose-xyloglucan framework by catalysing cleavage and re-ligation of the xyloglucan chains in the plant cell wall, and are considered cell wall loosening agents. In the laboratory, it has been isolated and characterised a XTH gene, ZmXTH1, from an elongation root cDNA library of maize. To address the cellular function of ZmXTH1, transgenic Arabidopsis thaliana plants over-expressing ZmXTH1 (under the control of the CaMV35S promoter) were generated. The aim of the work performed was therefore the characterisation of these transgenic plants at the ultrastructural level, by transmission electron microscopy (TEM).The detailed cellular phenotype of transgenic plants was investigated by comparing ultra-thin transverse sections of basal stem of 5-weeks old plants of wild type (Col 0) and 35S-ZmXTH1 Arabidopsis plants. Transgenic plants show modifications in the cell walls, particularly a thicker middle lamella layer with respect the wild type plants, supporting the idea that the overexpression of ZmXTH1 could imply a pronounced wall-loosening. In sum, the work carried out reinforces the idea that ZmXTH1 is involved in the cell wall loosening process in maize.