Transient expression of clusterin (sulfated glycoprotein-2) during development of rat pancreas

Abstract

Clusterin has been known to play important roles not only in remodeling damaged tissues, but also in tissue reorganization during embryonic development. In the present study, we have investigated the expression of clusterin in the endocrine pancreas during embryonic development. Although a weak immunoreaction was detected in some pancreatic primordial cells at day 14 of gestation, distinct clusterin expression was identified by immunocytochemistry and Northern blot analysis at the 16th day of gestation. Clusterin-producing cells, which corresponded to insulin-containing cells, accounted for the major portion of the developing islet of Langerhans up to 18 days of gestation. Thereafter, clusterin-producing cells display similar distribution and morphological features to glucagon-producing cells. Clusterin expressed in the pancreas was shown by Western blot analysis to be a disulfide-linked heterodimer of 70 kDa with an -subunit of 32 kDa. During early developmental stages, however, we found that proteolytic internal cleavage of the clusterin molecule occurred from the 18th day of gestation. Only one 70 kDa band on the 16th day and two bands (32 kDa and 70 kDa) on the 18th day of gestation were detected by Western blot analysis even in reducing conditions, while only a single 32 kDa band was detected on the second day after birth. The levels of clusterin mRNA in the pancreas transiently increased from the 16th day of gestation to the second day after birth, during the period when active cellular reorganization takes place to form the classic cellular features of the islet. Among various tissues (kidney, brain, liver, heart, lung and pancreas) the levels of clusterin mRNA were the highest in the pancreas from the 18th day of gestation to the second day after birth. In contrast, the lowest expression was observed in adult pancreatic tissue. The higher expression of clusterin in developing pancreas must indicate its involvement in tissue organization during development.

Clusterin expression during regeneration of pancreatic islet cells in streptozotocin-induced diabetic rats

“…Clusterin is known to be up-regulated at sites of tissue remodelling through differentiation and proliferation after apoptosis [10,14,16,41]. We have reported the expression of clusterin in the developing pancreas and in the pancreatic tissue of the streptozotocin treated rats and suggested that this protein must play important roles [7,20]. Therefore, we examined whether the expression of clusterin is associated with islet-cell replication and with islet reorganization in diabetic animal models.…”

“…It has not been defined whether the clusterin is directly involved in cell proliferation and differentiation. It could function as a cell signalling molecule involved in proliferation and differentiation after being expressed from surviving islet cells [7,20]. Clusterin was found within the secretory granules of the various cell types including pancreatic alpha cells [7].…”

“…To identify the proliferating cells to clusterin immunoreactivity, double immunostaining was carried out on the same sections using a mouse anti-PCNA (1:150, Zymed Lab. San Francisco, Calif., USA) and clusterin antibodies as described previously [20]. After immunostaining for PCNA, the tissue sections were treated for 90 s with vigorous agitation in a solution composed of 0.25 % potassium permanganate (1 volume), 5 % H 2 SO 4 (1 volume) and distilled water (140 volume) to elute tissue-bound PCNA antibody.…”

“…During development, it was transiently expressed in both alpha and beta cells [20]. Clusterin was also up-regulated in pancreatic cells in response to streptozotocin injection particularly in the surviving alpha cells, which reflected its cytoprotective role.…”

From Humans to Experimental Models: The Cytoprotective Role of Clusterin in the Kidney

“…During rodent embryogenesis, CLU expression is detected in a variety of the tissues in many developing organs, such as the epithelial cells of comma and S-shaped bodies of the primordial kidney [61], developing islet of Langerhans of the primordial pancreas [62], myocardial cells adjacent to developing endocardial cushions of both atrioventricular canal and truncusarteriosus, stromal connective tissue throughout leaflet formation of the developing hearts [63], hypothalamic region, neocortex and hippocampus of the developing brain [64,65]. Interestingly however, complete knockout (KO) of CLU expression in CLU KO mice has not been found to cause any phenotypic change in postnatal development as compared to WT mice [66], suggesting that CLU may not be absolutely required for the differentiation and morphogenesis of an organ (i.e.…”