Effect of variations in dietary Pi intake on intestinal Pi transporters (NaPi-IIb, PiT-1, and PiT-2) and phosphate-regulating factors (PTH, FGF-23, and MEPE).

Hyperphosphatemia is a common condition in patients with chronic kidney disease (CKD) and can lead to bone disease, vascular calcification, and increased risks of cardiovascular disease and mortality. Inorganic phosphate (Pi) is absorbed in the intestine, an important step in the maintenance of homeostasis. In CKD, it is not clear to what extent Pi absorption is modulated by dietary Pi. Thus, we investigated 5/6 nephrectomized (Nx) Wistar rats to test whether acute variations in dietary Pi concentration over 2 days would alter hormones involved in Pi metabolism, expression of sodium-phosphate cotransporters, apoptosis, and the expression of matrix extracellular phosphoglycoprotein (MEPE) in different segments of the small intestine. The animals were divided into groups receiving different levels of dietary phosphate: low (Nx/LPi), normal (Nx/NPi), and high (Nx/HPi). Serum phosphate, fractional excretion of phosphate, intact serum fibroblast growth factor 23 (FGF-23), and parathyroid hormone (PTH) were significantly higher and ionized calcium was significantly lower in the Nx/HPi group than in the Nx/LPi group. The expression levels of NaPi-IIb and PiT-1/2 were increased in the total jejunum mucosa of the Nx/LPi group compared with the Nx/HPi group. Modification of Pi concentration in the diet affected the apoptosis of enterocytes, particularly with Pi overload. MEPE expression was higher in the Nx/HPi group than in the Nx/NPi. These data reveal the importance of early control of Pi in uremia to prevent an increase in serum PTH and FGF-23. Uremia may be a determining factor that explains the expressional modulation of the cotransporters in the small intestine segments.

Co-localization of nestin and insulin and expression of islet cell markers in long-term human pancreatic nestin-positive cell cultures.

Strategies to differentiate progenitor cells into beta cells in vitro have been considered as an alternative to increase beta cell availability prior to transplantation. It has recently been suggested that nestin-positive cells could be multipotential stem cells capable of expressing endocrine markers upon specific stimulation; however, this issue still remains controversial. Here, we characterized short- and long-term islet cell cultures derived from three different human islet preparations, with respect to expression of nestin and islet cell markers, using confocal microscopy and semi-quantitative RT-PCR. The number of nestin-positive cells was found to be strikingly high in long-term cultures. In addition, a large proportion (49.7%) of these nestin-positive cells, present in long-term culture, are shown to be proliferative, as judged by BrdU incorporation. The proportion of insulin-positive cells was found to be high in short-term (up to 28 days) cultures and declined thereafter, when cells were maintained in the presence of 10% serum, concomitantly with the decrease in insulin and PDX-1 expression. Interestingly, insulin and nestin co-expression was observed as a rare event in a small proportion of cells present in freshly isolated human islets as well as in purified islet cells cultured in vitro for long periods of time. In addition, upon long-term subculturing of nestin-positive cells in 10% serum, we observed reappearance of insulin expression at the mRNA level; when these cultures were shifted to 1% serum for a month, expression of insulin, glucagon and somatostatin was also detected, indicating that manipulating the culture conditions can be used to modulate the nestin-positive cell's fate. Attempts to induce cell differentiation by plating nestin-positive cells onto Matrigel revealed that these cells tend to aggregate to form islet-like clusters, but this is not sufficient to increase insulin expression upon short-term culture. Our data corroborate previous findings indicating that, at least in vitro, nestin-positive cells may undergo the early stages of differentiation to an islet cell phenotype and that long-term cultures of nestin-positive human islet cells may be considered as a potential source of precursor cells to generate fully differentiated/ functional beta cells.