Fibroblastic cultures from the diabetic db/db mouse. Demonstration of decreased insulin receptors and impaired responses to insulin

Cellular Senescence as the Pathogenic Hub of Diabetes-Related Wound Chronicity

Diabetes is constantly increasing at a rate that outpaces genetic variation and approaches to pandemic magnitude. Skin cells physiology and the cutaneous healing response are progressively undermined in diabetes which predisposes to lower limb ulceration, recidivism, and subsequent lower extremities amputation as a frightened complication. The molecular operators whereby diabetes reduces tissues resilience and hampers the repair mechanisms remain elusive. We have accrued the notion that diabetic environment embraces preconditioning factors that definitively propel premature cellular senescence, and that ulcer cells senescence impair the healing response. Hyperglycemia/oxidative stress/mitochondrial and DNA damage may act as major drivers sculpturing the senescent phenotype. We review here historical and recent evidences that substantiate the hypothesis that diabetic foot ulcers healing trajectory, is definitively impinged by a self-expanding and self-perpetuative senescent cells society that drives wound chronicity. This society may be fostered by a diabetic archetypal secretome that induces replicative senescence in dermal fibroblasts, endothelial cells, and keratinocytes. Mesenchymal stem cells are also susceptible to major diabetic senescence drivers, which accounts for the inability of these cells to appropriately assist in diabetics wound healing. Thus, the use of autologous stem cells has not translated in significant clinical outcomes. Novel and multifaceted therapeutic approaches are required to pharmacologically mitigate the diabetic cellular senescence operators and reduce the secondary multi-organs complications. The senescent cells society and its adjunctive secretome could be an ideal local target to manipulate diabetic ulcers and prevent wound chronification and acute recidivism. This futuristic goal demands harnessing the diabetic wound chronicity epigenomic signature.

Glucose induces clonal selection and reversible dinucleotide repeat expansion in mesangial cells isolated from glomerulosclerosis-prone mice

Clonal selection has been proposed as a pathogenetic mechanism in various chronic diseases, such as scleroderma, hypertension, pulmonary fibrosis, interstitial fibrosis of the kidney, atherosclerosis, and uterine leiomyomatosis. We previously found that mesangial cells from ROP mice prone to develop glomerulosclerosis changed their phenotype in response to high glucose concentrations. Here, we investigate whether clonal selection might contribute to this phenotype change. We found that in ROP mice at least two distinct mesangial cell clones exist. They are characterized by a different length of the d(CA) repeat in the MMP-9 promoter and exhibit a significantly different gene expression profile. Exposure of ROP mesangial cells to 25 mmol/l glucose for 35 days induces both clonal selection and reversible dinucleotide repeat expansion. None of these findings were present in mesangial cells isolated from C57BL/6 mice, which are not sclerosis-prone. We conclude that mesangial cell michrochimerism may be a marker for the susceptibility to glomerulosclerosis, that dinucleotide repeat expansion may be a novel mechanism for glucose-induced changes in gene expression, and that clonal selection may partially explain the change in mesangial cell phenotype in diabetes.

Association of a decreased number of d(CA) repeats in the matrix metalloproteinase-9 promoter with glomerulosclerosis susceptibility in mice

The genetic background plays an important role in the development of progressive glomerulosclerosis. However, no marker is available for the reliable prediction of genetic susceptibility to glomerulosclerosis. Because matrix metalloproteinase-9 (MMP-9) levels are decreased in models of glomerulosclerosis and MMP-9 promoter polymorphism has been observed among patients with diabetic nephropathy, MMP-9 could be one such marker. The object of this study was to determine whether MMP-9 promoter polymorphism was associated with altered MMP-9 expression in mesangial cells (MC) from two mouse strains, i.e., ROP (glomerulosclerosis prone) and B6SJL (glomerulosclerosis resistant). ROP MC expressed 12-fold less MMP-9 mRNA. The MMP-9 promoter in ROP MC contained fewer d(CA) repeats, which was associated with lower MMP-9 expression and activity. Phorbol-12-myristate-13-acetate (3 to 60 ng/ml) increased MMP-9 expression in both MC types (3- to 4.5-fold), but the level in ROP MC never reached that in B6SLJ MC. Although reciprocal transfection of ROP and B6SJL MMP-9 promoter constructs into B6SJL and ROP cells revealed that the promoters were functional in both cell types, the B6SJL promoter was less responsive to phorbol-12-myristate-13-acetate stimulation when transfected into ROP MC, suggesting a role for other factors. In conclusion, the MMP-9 promoter exhibits a decreased number of d(CA) repeats in the sclerosis-prone strain. Because fewer d(CA) repeats associated with decreased MMP-9 expression in MC, it might be a genetic marker for glomerulosclerosis.

Chicken insulin discriminates between receptors for insulin and insulin-like growth factor I on centrally- and peripherally-derived glial cells

Insulin and IGF-I receptors in G26-20 cells, derived from a mouse oligodendroglioma, and in RN-2 cells, derived from a rat Schwannoma, were characterized by specific binding to [125I]insulin and [125I]IGF-I respectively. In both cell lines, the Kd for insulin was 1.5 nM. Insulin receptor number was 33,000/cell for RN-2 cells and 17,000 receptors/cell for G26-20 cells. RN-2 cells have 700,000 IGF-I receptors/cell with a Kd of 2 nM while G26-20 cells have 60,000 receptors/cell with an affinity of 4.9 nM. However, the independence of these two receptor populations in each cell type was equivocal since the subunit structure of these receptors appears identical by electrophoresis. In both cell lines, competition with insulin analogs for [125I]insulin binding demonstrated chicken insulin > insulin > IGF-I. Competition for [125I]IGF-I binding showed that IGF-I was approximately 85-fold more potent than insulin. Chicken insulin was ineffective at all concentrations. Thus, chicken insulin can be used as a specific ligand to unequivocally discriminate between IGF-I and insulin receptors and effects.

Analysis of interaction between insulin binding and insulin effect on primary culture of normal and db/db mouse hepatocytes

Insulin binding and the characteristics of insulin receptors were studied in primary cultures of hepatocytes isolated from genetically diabetic mice (db/db mice). In addition glycogen synthesis in these hepatocytes was studied as one of the indicators of insulin action after binding to the receptors. The maximum insulin binding of db/db mice hepatocytes was 46% of control. There was no significant difference in insulin binding affinity between db/db and normal mice hepatocytes. In db/db mice, no insulin effect on glycogen synthesis was recognized. On the contrary, in the experiment on hepatocytes from normal mice exposed to insulin to induce down-regulation of insulin receptors (insulin-pretreated), the effect of insulin on glycogen synthesis was less but maintained. After re-culture of the insulin-pretreated hepatocytes with insulin-free medium, insulin binding and the insulin effect were restored. However, no apparent changes of insulin binding or the insulin effect on glycogen synthesis were recognized in hepatocytes from db/db mice under the same condition. These results suggested that the impaired process after insulin binding might play an important role, in addition to the decreased capacity of insulin binding, in the pathogenesis of DM in db/db mice.

Insulin effect on GABA uptake in astroglial primary cultures

Astroglial cultures from newborn mouse cerebral cortex contain [125I]Insulin binding sites. Binding was specific, reversible, time dependent and reached equilibrium after 45 min. Insulin analogues compete for this [125I]Insulin binding. Incubation of cerebral cortex astroglial cultures with insulin induced a time- and dose-dependent inhibition of the [3H]GABA high affinity uptake. A decrease in the Vmax rather than an effect on the Km was observed. This effect was dose-dependent and effective at 10(-10) M. Autoradiographic observations on the cell monolayer showed the presence of two groups of cells: one which strongly takes up [3H]GABA and consist in smaller GFAP positive process-bearing cells and another group of much flatter and larger GFAP positive cells which uptake was lower. The smaller stellate cells were apparently the most sensitive to insulin effect. These results: 1) confirm the presence of insulin binding sites on astroglial primary cultures, 2) show an effect of insulin on [3H]GABA high affinity uptake of these cells; this effect being optimal on a stellate-like population of astrocytes, and 3) indicate that insulin may interfere in neuromodulation through astroglial signals.

Insulin receptor tyrosine kinase activity is unaltered in ob/ob and db/db mouse skeletal muscle membranes

Insulin binding and insulin receptor tyrosine kinase activity were examined in two rodent models with genetic insulin resistance using partially-purified skeletal muscle membrane preparations. Insulin binding activity was decreased about 50% in both 12-week (219 +/- 184 vs 1255 +/- 158 fmoles/mg, p less than 0.01) and 24-week old (2120 +/- 60 vs 1081 +/- 60 fmoles/mg, p less than 0.01) ob/ob mice. In contrast, insulin binding to membrane derived from 24-week old db/db mice was not significantly different from lean controls (1371 +/- 212 vs 1253 +/- 247 fmoles/mg). Insulin-associated tyrosine kinase activity of membranes from ob/ob skeletal muscle was decreased, compared to its normal lean littermate, when compared on a per mg of protein basis in both 12-week (37 +/- 3 vs 21 +/- 3 pmoles/min/mg, p less than 0.05) and 24-week old (71 +/- 5 vs 37 +/- 6 pmoles/min/mg, p less than 0.01) mice. However, no significant differences in kinase activities were observed when the data were normalized and compared on a per fmole of insulin-binding activity basis for the 12-week (12 +/- 1 vs 11 +/- 2) and 24-week (27 +/- 2 vs 20 +/- 3) age groups. Insulin receptor tyrosine kinase activity of db/db skeletal muscle membranes was not different than its normal lean littermate whether expressed on a protein (34 +/- 7 vs 30 +/- 3) or fmole of insulin-binding activity (21 +/- 4 vs 18 +/- 4) basis. These data suggest that insulin receptor tyrosine kinase is not associated with the insulin resistance observed in ob/ob and db/db mice and demonstrate differences in receptor regulation between both animal models.

Vasopressin, angiotensin and adrenergic receptors of rat liver Golgi fractions--molecular weight of the angiotensin-receptor irreversible complex after in vitro and in vivo labelling

The binding of vasopressin, angiotensin II and prazosin (alpha 1-adrenergic antagonist) to purified heavy (GH) and (intermediate + light) (GI + L) rat liver Golgi fractions was studied. The three types of ligands showed a saturable and specific binding in Golgi fractions; the maximal specific binding of [3H]vasopressin, [3H]prazosin and [125I]Sar-N3-Phe-angiotensin II was respectively 5-10%, 20-30% and 30-40% of that detected in purified plasma membranes. The apparent binding affinities of the three ligands were the same whether determined in Golgi fractions or plasma membranes. The presence of vasopressin, alpha 1-adrenergic and angiotensin receptors in very different proportions, as compared to the amount of receptor detected in plasma membranes, in GH and GI + L Golgi fractions was not compatible with the idea that a plasma membrane impurity accounted for the detection of receptor in the purified intracellular particulate fractions. In vivo injection of [125I]Sar-N3-Phe-angiotensin II resulted in a receptor-mediated endocytosis of the iodo-angiotensin analog into the GH and GI + L Golgi fractions. The apparent molecular weight of the irreversible complex, [125I]angiotensin-receptor, was estimated in subcellular fractions using SDS-PAGE electrophoresis. This value was identical after either in vivo or in vitro labelling (MW = 63,000) and was indistinguishable from the molecular weight of the irreversible hormone receptor complex present in the plasma membranes.

Identification of insulin receptors on rat Sertoli cells

The binding of insulin to rat Sertoli cells was investigated to establish if effects of insulin on Sertoli cells can be mediated via insulin receptors. Sertoli cells were isolated from the testes of 3-week-old rats, and preincubated for 3 days in the absence of hormones. Binding of 125I-porcine insulin to the Sertoli cells was 75-80% specific and this binding was time- and pH-dependent and reversible. Scatchard analysis of the binding data resulted in curvilinear plots with a high affinity binding of Kd = 1.8 X 10(-9) M. Porcine and bovine insulin competed equally well for 125I-porcine insulin binding. Porcine proinsulin was 10-50 times less potent, corresponding to its lower biological activity. Insulin-like growth factor-I (IGF-I) was 30-40 times less potent, indicating low affinity binding of IGF-I to the insulin receptor. Lutropin which was used as a control gave no competition with the 125I-insulin binding. Affinity labelling of Sertoli cell membrane proteins with 125I-insulin using the cross-linking agent disuccinimidylsuberate revealed binding of insulin to (a) protein(s) of Mr greater than 300,000 or Mr = 130,000 after electrophoresis under non-reducing or reducing conditions, respectively. Affinity labelling with 125I-insulin was largely prevented by unlabelled insulin. It is concluded that the protein of Mr 130,000 may represent the alpha-subunit of the insulin receptor. The presence of insulin receptors as well as IGF-I receptors on cultured rat Sertoli cells may suggest that insulin and IGF-I have specific functions in regulating the maturation and activities of Sertoli cells during the initiation and maintenance of spermatogenesis.

Adipose tissue cellularity and growth characteristics of unselected and selected broilers: implications for the development of body fat

Chicks from large and small eggs were used to increase body weight range within samples of unselected Athens-Canadian (AC) and commercial Cobb (C) broilers. At 54 days of age, representatives of each sex and broiler stock obtained from the large and small eggs were killed. Indices of whole body, muscle, fat, and bone growth were taken. Samples of abdominal fat were fixed with osmium tetroxide for electronic quantification of adipocyte number and size distribution. Broiler stock, egg size, and sex affected all indices of muscle and bone growth on an absolute basis, but only broiler stock significantly affected abdominal fat pad development. Muscle and fat weight, expressed as a proportion of body weight, were larger in C broilers. Abdominal adipocyte number was greater in C than AC (126.0 +/- 10.0 vs. 90.9 +/- 7.7 million, P less than .01), but the greater adiposity of C was associated with an increase in adipocyte size. If the mean adipocyte volume of C (120.4 +/- 8.5 pl) was reduced to the mean adipocyte volume of AC (53.8 +/- 6.5 pl), proportional weight of the abdominal pad of C would have been smaller than proportional pad weight of AC. The problem of excessive abdominal fat deposition in the selected broiler stock appears related to factors that affect control of adipocyte size and body composition.

Increased turnover of surface insulin receptors in fibroblastic cultures from genetically diabetic (DB/DB) mice

The turnover of surface insulin receptors in fibroblastic cultures from genetically diabetic (db/db) mice and nondiabetic (m/m) littermates has been determined by combining a heavy isotope density shift technique with cross-linking of insulin to surface receptors. Our results indicate that the surface insulin receptors turn over faster in diabetic cells than in nondiabetic cells. In addition, fewer receptors are incorporated into the plasma membrane per hour in diabetic cells than in nondiabetic cells. It is possible to propose a model to account for the altered expression of surface insulin receptors in diabetic cells on the basis of abnormalities of receptor incorporation and turnover.

Absence of down-regulation of insulin receptors in human breast cancer cells (MCF-7) cultured in serum-free medium: comparison with epidermal growth factor

MCF-7 cells were cultured either in RPMI-1640 medium containing 10% fetal calf serum (FCS) or in a serum-free (SF) medium supplemented with insulin, epidermal growth factor (EGF) and transferrin. Binding studies were performed with 125I-insulin or 125I-EGF. In the FCS containing culture, down-regulation was seen for insulin receptors (47%), and for the EGF receptors (75%). Using cells grown in the serum-free medium we could not demonstrate down-regulation of the insulin receptors, while the EGF receptors were down-regulated to the same extent (74%). The number of binding sites per cell was about twice as much in cells cultured in FCS as that in SF medium. No significant differences were observed for receptor affinity of insulin or EGF in cells grown in both media. The rate of internalization of insulin or EGF into cells was similar in both culture conditions. The mechanism in which only EGF but not insulin demonstrated receptor down-regulation in SF medium remains unknown.

Reduction in hepatic but not in renal and vascular vasopressin receptor number in hyperinsulinemic mice and rats

Hepatic plasma membranes of female obese mice C57 BL-6 orl ob/ob (ob/ob mice) completely lack vasopressin (VP) receptors of the V1 type whereas kidney VP receptors are normally expressed and functionally coupled to adenylate cyclase. To discover if these alterations are linked to a genetic defect of the V1 receptor, we have studied the binding of VP on liver and kidney membranes of two other models, female diabetic mice C57 BL-6 orl db/db (db/db mice) and female Zucker rats Fatty/orl fa/fa (fa/fa rats), which exhibit different temporal pattern of obesity, hyperinsulinemia and insulin resistance. In addition, since VP is known to exert its vascular response through stimulation of V1 receptors, we have studied the reactivity of VP of isolated tail artery in the three different models, ob/ob and db/db mice and fa/fa rats, and in their respective controls. In all cases, VP kidney receptors and VP vascular reactivity are normal. db/db mice exhibit a marked decrease in hepatic VP receptors whereas a 50% decrease was observed in 32 week fa/fa rats. Angiotensin II and prazosin binding sites are still present as well as the adenylate cyclase response to glucagon. These results suggest that the specific alteration in liver VP receptors is not related to a defect in V1 receptor genetic expression but is specific for liver and appears to parallel the level of hyperinsulinemia and/or insulin resistance.

The effects of insulin and tunicamycin on insulin receptors of cultured fibroblasts

The effect of down-regulation on the intracellular pool of insulin receptors and the role of glycosylation in recovery from down-regulation have been studied in fibroblastic cultures from the skin of non-diabetic mice. In control cultures, 55% of the total specific [125I]insulin-binding activity was in the intracellular compartment. Insulin caused a time- and concentration-dependent decrease in the number of cell surface insulin receptors, with no significant change in total insulin receptors. This decrease in surface receptors was accompanied by an increase in the specific binding of [125I]insulin in the intracellular compartment. Removal of insulin from down-regulated cells resulted in a time-dependent increase in the binding of [125I]insulin to surface receptors, reaching 90% of that in controls by 12 h. The recovery of surface insulin receptors after removal of insulin was blocked by incubation of cultures with tunicamycin, but not by cycloheximide. These results indicate that down-regulation of surface insulin receptors by insulin is associated with translocation of receptors into the intracellular pool and suggest that protein glycoslylation is important in insulin receptor recycling and externalization.

Reduced binding of epidermal growth factor by avian sarcoma virus-transformed rat cells

Rat cells transformed by Rous sarcoma virus and Fujinami sarcoma virus bound 5-10% of the amount of epidermal growth factor (EGF) bound by normal cells. Scatchard plot analysis indicated that the reduction in binding by transformed cells was due to a decreased number of receptors rather than to altered binding affinity. In experiments with temperature sensitive mutants of Rous sarcoma virus and Fujinami sarcoma virus significant loss of EGF binding occurred within one hour of shift from non-permissive to permissive temperature. Conditioned media from various normal and transformed cell lines were examined for the ability to inhibit EGF binding to normal cells or to cause "down regulation" of EGF receptors. No activity of either type was found. EGF-dependent phosphorylation in isolated membrane preparations was also examined. Membranes from normal cells displayed EGF-dependent phosphorylation of a Mr 180,000 protein presumed to be the EGF receptor. This activity was absent in membranes from transformed cells. The data suggest a close correlation between activation of avian sarcoma virus transforming gene products and modulation of the EGF growth regulatory system.

Insulin binding in cultured Chinese hamster kidney epithelial cells: the effect of serum in the medium

[125I] Insulin (porcine) binding to an epithelial cell line established from a Chinese hamster kidney, CHK-AC E-100, showed an optimum at pH 8.0 and reached a maximum after 2.5 h incubation at 25 degrees C. Dissociation of bound [125I] insulin was facilitated by the addition of unlabeled insulin in the dilution buffer. Porcine insulin effectively competed for [125I] insulin binding to the cultured cells and was 30 and 90 times as potent as guinea pig insulin and porcine proinsulin in causing 50% inhibition of [125I] insulin binding; glucagon was completely ineffective. Scatchard analysis of the binding data yielded a curvilinear plot and a capacity of 0.6 ng/10(6) cells; the average affinity of the empty receptor, Ke, was calculated to be 1.78 X 10(6) M-1 and that of the filled receptor, Kf, 0.57 X 10(8) m-1, Substitution of fetal bovine serum (FBS) in the culture medium with bovine calf, bovine newborn, of bovine calf serum altered insulin binding characteristics in the cells and reduced cell growth. Insulin binding characteristics of cells grown in hormone-supplemented medium containing 0 to 0.1% FBS were similar to those of cells grown in minimum essential medium (MEM) containing 2 to 5% FBS. The data indicated that the established Chinese hamster kidney epithelial cell line CHK-AC E-100 possessed specific insulin receptors and the characteristics of the receptors could be manipulated by changing the serum in culture medium.