HBA1C AND MEAN GLUCOSE DERIVED FROM SHORT-TERM CONTINUOUS GLUCOSE MONITORING ASSESSMENT DO NOT CORRELATE IN PATIENTS WITH HBA1C >8.

OBJECTIVE: Optimum therapy for patients with diabetes depends on both acute and long-term changes in plasma glucose, generally assessed by glycated hemoglobin (HbA1c) levels. However, the correlation between HbA1c and circulating glucose has not been fully determined. Therefore, we carefully examined this correlation when glucose levels were assessed by continuous glucose monitoring (CGM). METHODS: Fifty-one patients (70% female, 30% male) were examined; among them were 28 with type 1 diabetes and 23 with type 2 diabetes. Clinically determined HbA1c levels were compared with blood glucose determined by CGM during a short time period. RESULTS: Changes in HbA1c levels up to 8.0% showed a clear and statistically strong correlation (R = 0.6713; P<.0001) with mean blood glucose levels measured by CGM, similar to that observed in the A1c-derived Average Glucose study in which patients were monitored for a longer period. However, we found no statistical correlation (R = 0.0498; P = .83) between HbA1c and CGM-assessed glucose levels in our patient population when HbA1c was >8.0%. CONCLUSION: Short-term CGM appears to be a good clinical indicator of long-term glucose control (HbA1c levels); however, cautions should be taken while interpreting CGM data from patients with HbA1c levels >8.0%. Over- or underestimation of the actual mean glucose from CGM data could potentially increase the risks of inappropriate treatment. As such, our results indicate that a more accurate analysis of CGM data might be useful to adequately tailor clinical treatments. ABBREVIATIONS: ADAG = A1c-Derived Average Glucose CGM = continuous glucose monitoring %CV = percent coefficient of variation HbA1c = glycated hemoglobin.

Autophagy in Myf5+ progenitors regulates energy and glucose homeostasis through control of brown fat and skeletal muscle development.

Macroautophagy (MA) regulates cellular quality control and energy balance. For example, loss of MA in aP2-positive adipocytes converts white adipose tissue (WAT) into brown adipose tissue (BAT)-like, enhancing BAT function and thereby insulin sensitivity. However, whether MA regulates early BAT development is unknown. We report that deleting Atg7 in myogenic Myf5+ progenitors inhibits MA in Myf5-cell-derived BAT and muscle. Knock out (KO) mice have defective BAT differentiation and function. Surprisingly, their body temperature is higher due to WAT lipolysis-driven increases in fatty acid oxidation in 'Beige' cells in inguinal WAT, BAT and muscle. KO mice also present impaired muscle differentiation, reduced muscle mass and glucose intolerance. Our studies show that ATG7 in Myf5+ progenitors is required to maintain energy and glucose homeostasis through effects on BAT and muscle development. Decreased MA in myogenic progenitors with age and/or overnutrition might contribute to the metabolic defects and sarcopenia observed in these conditions.

Fyn Phosphorylates Transglutaminase 2 (Tgm2) and Modulates Autophagy and p53 Expression in the Development of Diabetic Kidney Disease.

Autophagy is involved in the development of diabetic kidney disease (DKD), the leading cause of end-stage renal disease. The Fyn tyrosine kinase (Fyn) suppresses autophagy in the muscle. However, its role in kidney autophagic processes is unclear. Here, we examined the role of Fyn kinase in autophagy in proximal renal tubules both in vivo and in vitro. Phospho-proteomic analysis revealed that transglutaminase 2 (Tgm2), a protein involved in the degradation of p53 in the autophagosome, is phosphorylated on tyrosine 369 (Y369) by Fyn. Interestingly, we found that Fyn-dependent phosphorylation of Tgm2 regulates autophagy in proximal renal tubules in vitro, and that p53 expression is decreased upon autophagy in Tgm2-knockdown proximal renal tubule cell models. Using streptozocin (STZ)-induced hyperglycemic mice, we confirmed that Fyn regulated autophagy and mediated p53 expression via Tgm2. Taken together, these data provide a molecular basis for the role of the Fyn-Tgm2-p53 axis in the development of DKD.

Integrative metabolic regulation of peripheral tissue fatty acid oxidation by the SRC kinase family member Fyn.

Mice null for Fyn (a member of the Src family of nonreceptor tyrosine kinases) display a reduced percentage of adipose mass associated with decreased adipocyte cell size. In parallel, there is a substantial reduction in fasting plasma glucose, insulin, triglycerides, and free fatty acids concomitant with decreased intrahepatocellular and intramyocellular lipid accumulation. Importantly, the Fyn null mice exhibit improved glucose tolerance resulting from increased peripheral tissue (adipose and skeletal muscle) insulin sensitivity with a very small effect in the liver. Moreover, whole-body, adipose, and skeletal muscle fatty acid uptake and oxidation are increased along with AMP kinase activation and acetyl-CoA carboxylase inhibition. Together, these data demonstrate crosstalk between Src-family kinase activity and fatty acid oxidation and show that the loss of Fyn markedly improves peripheral tissue insulin sensitivity by relieving a selective negative modulation of AMP kinase activity in adipose tissue and skeletal muscle.

Dietary cholecalciferol and calcium levels in a Western-style defined rodent diet alter energy metabolism and inflammatory responses in mice.

Male and female C57Bl6 mice were fed a control AIN76A diet, a new Western-style diet (NWD1) reflecting dietary patterns linked to elevated colon cancer incidence (higher fat, lower cholecalciferol, calcium, methyl donors, fiber), or NWD1 with elevated cholecalciferol and calcium (NWD2) from weaning. After 24 wk, serum 25-hydroxyvitamin D [25(OH)D] decreased by >80% in the NWD1 group compared with controls, but with no alteration in serum calcium or bone mineral density. The decreased serum 25(OH)D was prevented in the NWD2 group. After 32 wk, the NWD1 group compared with controls reduced overall energy expenditure by 15% without altering food consumption or physical activity and induced glucose intolerance, phenotypes associated with metabolic syndrome. These responses were unexpectedly exacerbated in the NWD2 group, further shifting mice toward greater fatty acid storage rather than oxidation compared with both control and NWD1 groups, but there was no change in physical activity, causing significant weight gain due to increased fat mass. The NWD1 group also exhibited inflammatory responses compared with controls, including macrophage-associated crown-like structures in epididymal adipose tissue and increased serum concentrations of the proinflammatory cytokine IL-1ß, and of its targets, MCP-1 and Rantes, which were prevented or greatly mitigated in the NWD2 group. However, there was also elevated lipid storage in the liver and steatosis not seen in the control and NWD1 groups. Thus, elevating cholecalciferol and calcium in a Western-style diet can reduce inflammation associated with risk for colon tumor development, but interaction of nutrients in this diet can compromise liver function when fed long term.

Lemon Extract Reduces Angiotensin Converting Enzyme (ACE) Expression and Activity and Increases Insulin Sensitivity and Lipolysis in Mouse Adipocytes.

Obesity is associated with insulin resistance and cardiovascular complications. In this paper, we examine the possible beneficial role of lemon juice in dieting. Lemon extract (LE) has been proposed to improve serum insulin levels and decrease angiotensin converting enzyme (ACE) activity in mouse models. ACE is also a biomarker for sustained weight loss and ACE inhibitors improve insulin sensitivity in humans. Here, we show that LE impacts adipose tissue metabolism directly. In 3T3-L1 differentiated adipocyte cells, LE improved insulin sensitivity as evidenced by a 3.74 ± 0.54-fold increase in both pAKT and GLUT4 levels. LE also induced lipolysis as demonstrated by a 16.6 ± 1.2 fold-change in pHSL protein expression levels. ACE gene expression increased 12.0 ± 0.1 fold during differentiation of 3T3-L1 cells in the absence of LE, and treatment with LE decreased ACE gene expression by 80.1 ± 0.5% and protein expression by 55 ± 0.37%. We conclude that LE's reduction of ACE expression causes increased insulin sensitivity and breakdown of lipids in adipocytes.

Angiotensin Converting Enzyme (ACE): A Marker for Personalized Feedback on Dieting.

Angiotensin Converting Enzyme (ACE) expression and activity is associated with obesity. ACE is a circulating factor that predicts sustained weight loss over a time frame of months. Here, we evaluate whether ACE might also be an early marker (over a 24-hour period) for weight loss. 32 participants (78% females; BMI 28.47 ± 4.87kg/m2) followed a 1200KCal diet with an optional daily (<250KCal) snack and were asked to use an in-house generated health platform to provide recordings of food intake, physical activity and urine collection time and volume. Following a day of dieting, ACE levels in urine negatively correlated with weight loss (p = 0.015 ). This reduction in ACE levels was significantly more robust in individuals with a BMI > 25 (p = 0.0025 ). This study demonstrated that ACE levels correlate with BMI and weight loss as early as after 1 day of dieting, and thus ACE could be a potential early "biofeedback" marker for weight loss and diet efficiency.

Dapagliflozin rescues endoplasmic reticulum stress-mediated cell death.

The new type 2 diabetes drug, dapagliflozin, reduces blood glucose levels and body weight by inhibiting sodium glucose transporter 2 (SGLT2) in proximal tubular cells. SGLT2 inhibitors might modulate glucose influx into renal tubular cells, thereby regulating the metabolic conditions that cause endoplasmic reticulum (ER) stress in the cells. In this study, we examined the effect of dapagliflozin on ER stress in the HK-2 proximal tubular cell line and in the kidney of db/db mice to characterise its function in diabetic nephropathy (DN). We found that dapagliflozin regulated ER stress-mediated apoptosis in vitro and in vivo. Only the elf2α-ATF4-CHOP pathway was regulated under these conditions. Notably, the drug rescued C2 ceramide-induced ER stress-mediated apoptosis and ER stress-mediated apoptosis, which might occur in DN, in db/db mice. Our study shows a novel role for dapagliflozin as an inhibitor of ER stress and suggests that dapagliflozin might be useful for the prevention of DN.

Placental extracellular vesicles express active dipeptidyl peptidase IV; levels are increased in gestational diabetes mellitus.

Gestational diabetes mellitus (GDM) is the most common metabolic disorder in pregnancy and is characterized by insulin resistance and decreased circulating glucagon-like peptide-1 (GLP-1). GDM resolves rapidly after delivery implicating the placenta in the disease. This study examines the biological functions that cause this pathology. The placenta releases syncytiotrophoblast-derived extracellular vesicles (STB-EVs) into the maternal circulation, which is enhanced in GDM. Dipeptidyl peptidase IV (DPPIV) is known to play a role in type 2 diabetes by breaking down GLP-1, which in turn regulates glucose-dependent insulin secretion. STB-EVs from control and GDM women were analysed. We show that normal human placenta releases DPPIV-positive STB-EVs and that they are higher in uterine than paired peripheral blood, confirming placental origin. DPPIV-bound STB-EVs from normal perfused placentae are dose dependently inhibited with vildagliptin. DPPIV-bound STB-EVs from perfused placentae are able to breakdown GLP-1 in vitro. STB-EVs from GDM perfused placentae show greater DPPIV activity. Importantly, DPPIV-bound STB-EVs increase eightfold in the circulation of women with GDM. This is the first report of STB-EVs carrying a biologically active molecule that has the potential to regulate maternal insulin secretion.

The Impact of Short-Term Professional Continuous Glucose Monitoring on Glycemic Control Via Lifestyle Improvement.

BACKGROUND: The efficacy of short-term professional continuous glucose monitoring (CGM) for glycemic control in patients with diabetes remains unclear. METHODS: We performed a 3-month study to evaluate the benefits of CGM in 64 patients. RESULTS: The overall glycemic control of patients who underwent CGM improved significantly; however, that of patients maintaining the same medications did not improve overall. Thirty-one patients with unchanged medications were divided into improved (n = 12) versus nonimproved (n = 19) groups. In the improved group, baseline hemoglobin A1c (HbA1c) levels were higher than in the nonimproved group (P = 0.0066) despite mean blood glucose levels remaining the same (P = 0.3406). The improved group also exhibited lower glucose variability. CONCLUSIONS: Patients with lower than expected mean glucose levels, based on HbA1c values, and patients with lower glucose level variability during CGM may be able to improve their glycemic control after lifestyle change without treatment modification.

Differential activation of Fyn kinase distinguishes saturated and unsaturated fats in mouse macrophages.

Diet-induced obesity is associated with increased adipose tissue activated macrophages. Yet, how macrophages integrate fatty acid (FA) signals remains unclear. We previously demonstrated that Fyn deficiency (fynKO) protects against high fat diet-induced adipose tissue macrophage accumulation. Herein, we show that inflammatory markers and reactive oxygen species are not induced in fynKO bone marrow-derived macrophages exposed to the saturated FA palmitate, suggesting that Fyn regulates macrophage function in response to FA signals. Palmitate activates Fyn and re-localizes Fyn into the nucleus of RAW264.7, J774 and wild-type bone marrow-derived macrophages. Similarly, Fyn activity is increased in cells of adipose tissue stromal vascular fraction of high fat-fed control mice, with Fyn protein being located in the nucleus of these cells. We demonstrate that Fyn modulates palmitate-dependent oxidative stress in macrophages. Moreover, Fyn catalytic activity is necessary for its nuclear re-localization and downstream effects, as Fyn pharmacological inhibition abolishes palmitate-induced Fyn nuclear redistribution and palmitate-dependent increase of oxidative stress markers. Importantly, mono-or polyunsaturated FAs do not activate Fyn, and fail to re-localize Fyn to the nucleus. Together these data demonstrate that macrophages integrate nutritional FA signals via a differential activation of Fyn that distinguishes, at least partly, the effects of saturated versus unsaturated fats.

Effect of carbohydrate counting using bolus calculators on glycemic control in type 1 diabetes patients during continuous subcutaneous insulin infusion.

The present study examined the long-term efficacy of insulin pump therapy for type 1 diabetes patients when carried out using carbohydrate counting with bolus calculators for 1 year. A total of 22 type 1 diabetes patients who had just started continuous subcutaneous insulin infusion were examined and divided into two groups: one that was educated about carbohydrate counting using bolus calculators (n = 14); and another that did not use bolus calculators (n = 8). After 1 year, the hemoglobin A1c levels of the patient group that used bolus calculators decreased persistently and significantly (P = 0.0297), whereas those of the other group did not. The bodyweight, total daily dose of insulin and bolus percentage of both groups did not change. Carbohydrate counting using bolus calculators is necessary to achieve optimal and persistent glycemic control in patients undergoing continuous subcutaneous insulin infusion.

Gestational diabetic transcriptomic profiling of microdissected human trophoblast.

Gestational diabetes mellitus (GDM), the most common metabolic complication of pregnancy, is influenced by the placenta, and its prevalence directly increases with obesity. Therefore, to define the aetiology of GDM requires that the confounding influence of obesity and the heterogeneous nature of the placenta impairing accurate quantitative studies be accounted for. Using laser capture microdissection (LCM), we optimized RNA extraction from human placental trophoblast, the metabolic cellular interface between mother and foetus. This allowed specific transcriptomic profiling of trophoblast isolated from GDM, and obese and normal human placentae. Genome-wide gene expression analysis was performed on the RNA extracted from the trophoblast of GDM and obese and normal placentae. Forty-five differentially expressed genes (DEGs) specifically discriminated GDM from matched obese subjects. Two genes previously linked with GDM, pregnancy specific beta-1 glycoprotein 6 (PSG6) and placental system A sodium-dependent transporter system (SLC38A1), were significantly increased in GDM. A number of these DEGs (8 ubiquitin-conjugating enzymes (UBE) splice variants (UBE2D3 variants 1, 3, 4, 5, 6, 7, and 9) and UBE2V1 variant 4)) were involved in RNA processing and splicing, and a significant number of the DEGs, including the UBE variants, were associated with increased maternal fasting plasma glucose.It is concluded that DEGs discriminating GDM from obese subjects were pinpointed. Our data indicate a biological link between genes involved in RNA processing and splicing, ubiquitination, and fasting plasma glucose in GDM taking into account obesity as the confounder.

Fyn phosphorylates AMPK to inhibit AMPK activity and AMP-dependent activation of autophagy.

We previously demonstrated that proto-oncogene Fyn decreased energy expenditure and increased metabolic phenotypes. Also Fyn decreased autophagy-mediated muscle mass by directly inhibiting LKB1 and stimulating STAT3 activities, respectively. AMPK, a downstream target of LKB1, was recently identified as a key molecule controlling autophagy. Here we identified that Fyn phosphorylates the α subunit of AMPK on Y436 and inhibits AMPK enzymatic activity without altering the assembly state of the AMPK heterotrimeric complex. As pro-inflammatory mediators are reported modulators of the autophagy processes, treatment with the pro-inflammatory cytokine TNFα resulted in 1) increased Fyn activity 2) stimulated Fyn-dependent AMPKα tyrosine phosphorylation and 3) decreased AICAR-dependent AMPK activation. Importantly, TNFα induced inhibition of autophagy was not observed when AMPKα was mutated on Y436. 4) These data demonstrate that Fyn plays an important role in relaying the effects of TNFα on autophagy and apoptosis via phosphorylation and inhibition of AMPK.

CD36 in myocytes channels fatty acids to a lipase-accessible triglyceride pool that is related to cell lipid and insulin responsiveness.

High levels of intramyocellular triglycerides are linked to insulin resistance and reflect conditions in which fatty acid uptake exceeds the myocyte oxidative capacity. CD36 facilitates fatty acid uptake by myocytes, and its level is increased in diabetic muscle. We examined whether high CD36 levels would increase lipid content and susceptibility of myocytes to fatty acid-induced insulin resistance. C2C12 myoblasts with stable fivefold overexpression of CD36 (+CD36) were generated and differentiated into myotubes. CD36 expression increased palmitate uptake, oxidation, and lipid incorporation but had no effect on cell triglyceride content. Importantly, glycerol release increased fourfold, indicating enhanced triglyceride turnover and suggesting that CD36 promotes futile cycling of fatty acids into triglyceride. When +CD36 myotubes were incubated with excess palmitate, CD36 enhancement of glycerol release was blunted, triglyceride content increased above wild-type cells, and insulin resistance of glucose metabolism was observed. In contrast to palmitate, oleate-treated +CD36 cells exhibited enhanced glycerol release and no alteration in triglyceride content or insulin responsiveness. Furthermore, increased expression of hormone-sensitive lipase was measured with CD36 expression and with oleate treatment. In conclusion, high futile cycling of fatty acids is important for maintaining low triglyceride content and insulin responsiveness of myocytes. The findings provide a new perspective related to the etiology of lipid accumulation and insulin resistance in myocytes.

Disruption of Fyn SH3 domain interaction with a proline-rich motif in liver kinase B1 results in activation of AMP-activated protein kinase.

Fyn-deficient mice display increased AMP-activated Protein Kinase (AMPK) activity as a result of Fyn-dependent regulation of Liver Kinase B1 (LKB1) in skeletal muscle. Mutation of Fyn-specific tyrosine sites in LKB1 results in LKB1 export into the cytoplasm and increased AMPK activation site phosphorylation. This study characterizes the structural elements responsible for the physical interaction between Fyn and LKB1. Effects of point mutations in the Fyn SH2/SH3 domains and in the LKB1 proline-rich motif on 1) Fyn and LKB1 binding, 2) LKB1 subcellular localization and 3) AMPK phosphorylation were investigated in C2C12 muscle cells. Additionally, novel LKB1 proline-rich motif mimicking cell permeable peptides were generated to disrupt Fyn/LKB1 binding and investigate the consequences on AMPK activity in both C2C12 cells and mouse skeletal muscle. Mutation of either Fyn SH3 domain or the proline-rich motif of LKB1 resulted in the disruption of Fyn/LKB1 binding, re-localization of 70% of LKB1 signal in the cytoplasm and a 2-fold increase in AMPK phosphorylation. In vivo disruption of the Fyn/LKB1 interaction using LKB1 proline-rich motif mimicking cell permeable peptides recapitulated Fyn pharmacological inhibition. We have pinpointed the structural elements within Fyn and LKB1 that are responsible for their binding, demonstrating the functionality of this interaction in regulating AMPK activity.

Mangiferin stimulates carbohydrate oxidation and protects against metabolic disorders induced by high-fat diets.

Excessive dietary fat intake causes systemic metabolic toxicity, manifested in weight gain, hyperglycemia, and insulin resistance. In addition, carbohydrate utilization as a fuel is substantially inhibited. Correction or reversal of these effects during high-fat diet (HFD) intake is of exceptional interest in light of widespread occurrence of diet-associated metabolic disorders in global human populations. Here we report that mangiferin (MGF), a natural compound (the predominant constituent of Mangifera indica extract from the plant that produces mango), protected against HFD-induced weight gain, increased aerobic mitochondrial capacity and thermogenesis, and improved glucose and insulin profiles. To obtain mechanistic insight into the basis for these effects, we determined that mice exposed to an HFD combined with MGF exhibited a substantial shift in respiratory quotient from fatty acid toward carbohydrate utilization. MGF treatment significantly increased glucose oxidation in muscle of HFD-fed mice without changing fatty acid oxidation. These results indicate that MGF redirects fuel utilization toward carbohydrates. In cultured C2C12 myotubes, MGF increased glucose and pyruvate oxidation and ATP production without affecting fatty acid oxidation, confirming in vivo and ex vivo effects. Furthermore, MGF inhibited anaerobic metabolism of pyruvate to lactate but enhanced pyruvate oxidation. A key target of MGF appears to be pyruvate dehydrogenase, determined to be activated by MGF in a variety of assays. These findings underscore the therapeutic potential of activation of carbohydrate utilization in correction of metabolic syndrome and highlight the potential of MGF to serve as a model compound that can elicit fuel-switching effects.

Fyn deficiency promotes a preferential increase in subcutaneous adipose tissue mass and decreased visceral adipose tissue inflammation.

Previous studies have demonstrated that Fyn knockout (FynKO) mice on a standard chow diet display increased glucose clearance and whole-body insulin sensitivity associated with decreased adiposity resulting from increased fatty acid use and energy expenditure. Surprisingly, however, despite a similar extent of adipose tissue (AT) mass accumulation on a high-fat diet, the FynKO mice remained fully glucose tolerant and insulin sensitive. Physiologic analyses demonstrated that the FynKO mice had a combination of skewed AT expansion into the subcutaneous compartment rather than to the visceral depot, reduced AT inflammation associated with reduced T-cell and macrophage infiltration, and increased proportion of anti-inflammatory M2 macrophages. These data demonstrate that Fyn is an important regulator of whole-body integrative metabolism that coordinates AT expansion, inflammation, and insulin sensitivity in states of nutrient excess. These data further suggest that inhibition of Fyn function may provide a novel target to prevent AT inflammation, insulin resistance, and the dyslipidemia components of the metabolic syndrome.

Alteration of de novo glucose production contributes to fasting hypoglycaemia in Fyn deficient mice.

Previous studies have demonstrated that glucose disposal is increased in the Fyn knockout (FynKO) mice due to increased insulin sensitivity. FynKO mice also display fasting hypoglycaemia despite decreased insulin levels, which suggested that hepatic glucose production was unable to compensate for the increased basal glucose utilization. The present study investigates the basis for the reduction in plasma glucose levels and the reduced ability for the liver to produce glucose in response to gluconeogenic substrates. FynKO mice had a 5-fold reduction in phosphoenolpyruvate carboxykinase (PEPCK) gene and protein expression and a marked reduction in pyruvate, pyruvate/lactate-stimulated glucose output. Remarkably, de novo glucose production was also blunted using gluconeogenic substrates that bypass the PEPCK step. Impaired conversion of glycerol to glucose was observed in both glycerol tolerance test and determination of the conversion of (13)C-glycerol to glucose in the fasted state. α-glycerol phosphate levels were reduced but glycerol kinase protein expression levels were not changed. Fructose-driven glucose production was also diminished without alteration of fructokinase expression levels. The normal levels of dihydroxyacetone phosphate and glyceraldehyde-3-phosphate observed in the FynKO liver extracts suggested normal triose kinase function. Fructose-bisphosphate aldolase (aldolase) mRNA or protein levels were normal in the Fyn-deficient livers, however, there was a large reduction in liver fructose-6-phosphate (30-fold) and fructose-1,6-bisphosphate (7-fold) levels as well as a reduction in glucose-6-phosphate (2-fold) levels. These data suggest a mechanistic defect in the allosteric regulation of aldolase activity.

Inhibition of Akt activity and calcium channel function coordinately drive cell-cell fusion in the BeWO choriocarcinoma placental cell line.

To establish a simple and quantitative live cell fusion assay for placental syncytialization, we generated stable GFP and dsRed expressing fusogenic BeWo cell lines. Fluorescent Activated Cell Sorting was shown to provide a quantitative determination of forskolin (cAMP-mediated) fusion in a time and concentration dependent manner consistent with the increased secretion of beta human chorionic gonadotrophin (ß-HCG) and appearance of multi-nucleated cells. Analyses of the fusion process demonstrated that in addition to increased cAMP levels, simultaneous reduction of intracellular calcium and inhibition of Type 1 phosphatidylinositol 3 kinase (PI3K)/Akt signaling also resulted in cell fusion. Although individual blockade of calcium channel function or PI3K/Akt signaling was without effect, the combination with forskolin resulted in a potentiation of cell fusion. These data demonstrate syncytialization is a complex process that depends upon the regulation of distinct signaling inputs that function in concert with each other.