Pancreatic fat cells of humans with type 2 diabetes display reduced adipogenic and lipolytic activity

Pro-Inflammatory Food, Gut Microbiota, and Cardiovascular and Pancreatic Diseases

Recent studies have shown that a pro-inflammatory diet and dysbiosis, especially a high level of trimethylamine-N-oxide (TMAO), are associated with various adverse health conditions. Cardiovascular diseases and pancreatic diseases are two major morbidities in the modern world. Through this narrative review, we aimed to summarize the association between a pro-inflammatory diet, gut microbiota, and cardiovascular and pancreatic diseases, along with their underlying mechanisms. Our review revealed that TMAO is associated with the development of cardiovascular diseases by promoting platelet aggregation, atherosclerotic plaque formation, and vascular inflammation. TMAO is also associated with the development of acute pancreatitis. The pro-inflammatory diet is associated with an increased risk of pancreatic cancer and cardiovascular diseases through mechanisms that include increasing TMAO levels, activating the lipopolysaccharides cascade, and the direct pro-inflammatory effect of certain nutrients. Meanwhile, an anti-inflammatory diet decreases the risk of cardiovascular diseases and pancreatic cancer.

Kruppel-like factor 5 enhances proliferation, lipid droplet formation and oxaliplatin resistance in colorectal cancer by promoting fatty acid binding protein 6 transcription

Oxaliplatin (OXA) is a standard agent for colorectal cancer (CRC) adjuvant chemotherapy. However, acquired and intrinsic OXA resistance is a primary challenge for CRC treatment. This study investigates the function of the Kruppel-like factor 5/fatty acid binding proteins 6 (KLF5/FABP6) axis in CRC proliferation, lipid droplet formation and OXA resistance. OXA-resistant CRC cell lines were constructed, and FABP6 and KLF5 expression was assessed in parental and OXA-resistant CRC cells. Subsequent to gain- and loss-of-function experiments, CRC cell proliferation was assessed by cell counting kit-8 (CCK-8) and clone formation assays, the intracellular lipid synthesis by oil red O staining and the protein expression of lipid metabolism genes by western blot. OXA resistance of CRC cells was assessed by CCK-8 assay. The binding of KLF5 to FABP6 was analyzed by the dual-luciferase reporter and ChIP assays. A tumorigenicity assay in nude mice was adopted to examine the impact of KLF5 on CRC tumor growth and OXA resistance in vivo . FABP6 and KLF5 expression was high in CRC cell lines. Downregulation of FABP6 or KLF5 restrained CRC cell proliferation and lipid droplet formation in vitro . FABP6 and KLF5 expression was elevated in OXA-resistant CRC cells. Downregulation of FABP6 or KLF5 repressed the OXA resistance of OXA-resistant CRC cells. Mechanistically, KLF5 facilitated the transcription of FABP6. FABP6 overexpression counteracted the suppressive effects of KLF5 downregulation on CRC cell growth, lipid droplet formation and OXA resistance. KLF5 downregulation restrained CRC tumor growth and OXA resistance in vivo . In conclusion, KLF5 knockdown reduced FABP6 transcription to protect against proliferation, lipid droplet formation and OXA resistance in CRC.

Pancreatic steatosis and metabolic pancreatic disease: a new entity?

Overweight and obesity are some of the most important health challenges. Many diseases are related to these metabolic disorders, and, among them, the pancreatic fat accumulation, also called "pancreatic steatosis" or "nonalcoholic fatty pancreas", seems to have an emerging role in different conditions. There are different method to evaluate the fat content in the pancreas, such as histology, different imaging techniques and endoscopic ultrasound, but there is no gold standard for the correct diagnosis and for the identification of "inter/intralobular" and "intra-acinar" pancreatic fat. However, the fat storage in the pancreas is linked to chronic inflammation and to several conditions, such as acute and chronic pancreatitis, type 2 diabetes mellitus and pancreatic cancer. In addition, pancreatic fat accumulation has also been demonstrated to play a role in surgical outcome after pancreatectomy, in particular for the development of postoperative pancreatic fistula. Different possible therapeutic approaches have been proposed, but there is still a lack of evidence. The aim of this review is to report the current evidence about the relationship between the obesity, the pancreatic fat accumulation and its potential role in pancreatic diseases.

Brown adipocyte activation mediates lipid metabolism through exosomal tRNA-derived fragments

Human obesity is related with intrinsic impairments of adipocyte lipolysis and ectopic lipid accumulation. Small regulatory RNAs, such as tRNA-derived fragments (tRFs) and tRNA halves (tiRNAs), are enriched in exosomes and play a crucial role in lipid metabolism. To determine certain tRFs for lipolysis, brown adipocytes were treated with forskolin. Using tRFs sequencing, 207 different expressed exosomal tRFs were determined. In forskolin samples, 145 downregulated and 62 upregulated tRFs were identified. Further, qRT-PCR validated that three notably upregulated tRFs (tRF-Gly-GCC-007, tRF-Gly-GCC-008, and tRF-Gly-GCC-009) were in accordance with the sequencing result. Target genes of tRFs were involved in positive regulation of protein phosphorylation and cell adhesion process by significantly downregulating UCHL1 expression, which might participate in lipolysis. This study might provide therapeutic targets and potential diagnostic biomarkers for obesity treatment.

Extracellular Matrix Expression in Human Pancreatic Fat Cells of Patients with Normal Glucose Regulation, Prediabetes and Type 2 Diabetes

Previously, we found that human pancreatic preadipocytes (PPAs) and islets influence each other and that the crosstalk with the fatty liver via the hepatokine fetuin-A/palmitate induces inflammatory responses. Here, we examined whether the mRNA-expression of pancreatic extracellular matrix (ECM)-forming and -degrading components differ in PPAs from individuals with normal glucose regulation (PPAs-NGR), prediabetes (PPAs-PD), and type 2 diabetes (PPAs-T2D), and whether fetuin-A/palmitate impacts ECM-formation/degradation and associated monocyte invasion. Human pancreatic resections were analyzed (immuno)histologically. PPAs were studied for mRNA expression by real-time PCR and protein secretion by Luminex analysis. Furthermore, co-cultures with human islets and monocyte migration assays in Transwell plates were conducted. We found that in comparison with NGR-PPAs, TIMP-2 mRNA levels were lower in PPAs-PD, and TGF-β1 mRNA levels were higher in PPAs-T2D. Fetuin-A/palmitate reduced fibronectin, decorin, TIMP-1/-2 and TGF-ß1 mRNA levels. Only fibronectin was strongly downregulated by fetuin-A/palmitate independently of the glycemic status. Co-culturing of PPAs with islets increased TIMP-1 mRNA expression in islets. Fetuin-A/palmitate increased MMP-1, usherin and dermatopontin mRNA-levels in co-cultured islets. A transmigration assay showed increased monocyte migration towards PPAs, which was enhanced by fetuin-A/palmitate. This was more pronounced in PPAs-T2D. The expression of distinct ECM components differs in PPAs-PD and PPAs-T2D compared to PPAs-NGR, suggesting that ECM alterations can occur even in mild hyperglycemia. Fetuin-A/palmitate impacts on ECM formation/degradation in PPAs and co-cultured islets. Fetuin-A/palmitate also enhances monocyte migration, a process which might impact on matrix turnover.

Effects of adrenergic-stimulated lipolysis and cytokine production on in vitro mouse adipose tissue-islet interactions

Inflammatory cytokines and non-esterified fatty acids (NEFAs) are obesity-linked factors that disturb insulin secretion. The aim of this study was to investigate whether pancreatic adipose tissue (pWAT) is able to generate a NEFA/cytokine overload within the pancreatic environment and as consequence to impact on insulin secretion. Pancreatic fat is a minor fat depot, therefore we used high-fat diet (HFD) feeding to induce pancreatic steatosis in mice. Relative Adipoq and Lep mRNA levels were higher in pWAT of HFD compared to chow diet mice. Regardless of HFD, Adipoq and Lep mRNA levels of pWAT were at least 10-times lower than those of epididymal fat (eWAT). Lipolysis stimulating receptors Adrb3 and Npr1 were expressed in pWAT and eWAT, and HFD reduced their expression in eWAT only. In accordance, HFD impaired lipolysis in eWAT but not in pWAT. Despite expression of Npr mRNA, lipolysis was stimulated solely by the adrenergic agonists, isoproterenol and adrenaline. Short term co-incubation of islets with CD/HFD pWAT did not alter insulin secretion. In the presence of CD/HFD eWAT, glucose stimulated insulin secretion only upon isoproterenol-induced lipolysis, i.e. in the presence of elevated NEFA. Isoproterenol augmented Il1b and Il6 mRNA levels both in pWAT and eWAT. These results suggest that an increased sympathetic activity enhances NEFA and cytokine load of the adipose microenvironment, including that of pancreatic fat, and by doing so it may alter beta-cell function.

Pancreatic Islets as a Target of Adipokines

Rising rates of obesity are intricately tied to the type 2 diabetes epidemic. The adipose tissues can play a central role in protection against or triggering metabolic diseases through the secretion of adipokines. Many adipokines may improve peripheral insulin sensitivity through a variety of mechanisms, thereby indirectly reducing the strain on beta cells and thus improving their viability and functionality. Such effects will not be the focus of this article. Rather, we will focus on adipocyte-secreted molecules that have a direct effect on pancreatic islets. By their nature, adipokines represent potential druggable targets that can reach the islets and improve beta-cell function or preserve beta cells in the face of metabolic stress. © 2022 American Physiological Society. Compr Physiol 12:1-27, 2022.

The Association of lncRNA and mRNA Changes in Adipose Tissue with Improved Insulin Resistance in Type 2 Obese Diabetes Mellitus Rats after Roux-en-Y Gastric Bypass

Objective

Roux-en-Y gastric bypass (RYGB) has shown good effects in improving obesity and type II diabetes mellitus (T2DM), but the underlying mechanisms remain unclear. This study explored the changes of related lncRNAs, mRNAs, and signaling pathways in white adipose tissue of T2DM rats after RYGB based on RNA-Seq sequencing, with the aim to provide a theoretical basis for RYGB treatment.

Methods

T2DM rat models were established by continuous feeding with a high-fat diet and injection of streptozotocin (STZ), after which they underwent RYGB or sham surgery. After the surgery, their body weight was measured weekly. Their fasting blood glucose (FBG) and fasting serum insulin (FSI) were also measured. A homeostasis model assessment of insulin resistance (HOMA-IR) was calculated at weeks 0, 8, and 12. Besides, white adipose tissue of T2DM rats was collected for RNA-Seq sequencing and validated by qRT-PCR. A series of bioinformatics analyses, such as differential expression genes (DEGs) screening, was performed. GO and KEGG functional enrichment analysis and protein-protein interaction (PPI) network construction were conducted based on the sequencing data.

Results

RYGB surgery could significantly inhibit the weight growth rate and decrease the FBG, FSI, and HOMA-IR of T2DM rats. Bioinformatics analysis of RNA sequencing (RNA-Seq) results revealed that 87 DE- lncRNAs (49 upregulated and 38 downregulated) and 1,824 DEGs (896 upregulated and 928 downregulated) were present in between the RYGB group and Sham group. GO and KEGG analysis showed that the target genes of DEGs and differentially expressed lncRNAs (DE-lncRNAs) were mainly associated with amino acid metabolism, fatty acid metabolism, channel activity, and other processes. In addition, the PPI network diagram also displayed that genes such as Fasn, Grin3a, and Nog could be key genes playing a role after RYGB. qRT-PCR showed that the expression level of Grin3a in the RYGB group was significantly increased compared with the Sham group, while the expression of Fasn and Nog was significantly decreased, which was consistent with the sequencing results.

Conclusion

Using RNA-Seq sequencing, this study revealed the changes of related lncRNAs, mRNAs, and signaling pathways in the white adipose tissue of T2DM rats after RYGB and identified Fasn, Grin3a, and Nog as potential key genes to function after RYGB.

Fatty Pancreas-Centered Metabolic Basis of Pancreatic Adenocarcinoma: From Obesity, Diabetes and Pancreatitis to Oncogenesis

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest types of cancer, and it is currently the third most common cause of cancer death in the U.S.A. Progress in the fight against PDAC has been hampered by an inability to detect it early in the overwhelming majority of patients, and also by the reduced oxygen levels and nutrient perfusion caused by new matrix formation through the activation of stromal cells in the context of desmoplasia. One harbinger of PDAC is excess intrapancreatic fat deposition, namely, fatty pancreas, which specifically affects the tumor macro- and microenvironment in the organ. Over half of PDAC patients have diabetes mellitus (DM) at the time of diagnosis, and fatty pancreas is associated with subsequent DM development. Moreover, there is a strong association between fatty pancreas and fatty liver through obesity, and a higher intrapancreatic fat percentage has been noted in acute pancreatitis patients with DM than in those without DM. All these findings suggest that the link between fatty pancreas and PDAC might occur through metabolic alterations, either DM-related or non-DM-related. Based on clinical, in vivo and in vitro evidence, the current review highlights the etiologies of fatty pancreas (including fatty infiltration and replacement) and the fatty pancreas-associated metabolic alterations involved in oncogenesis to provide crucial targets to prevent, detect, and/or effectively treat PDAC.

Metabolic implications of pancreatic fat accumulation

Fat accumulation outside subcutaneous adipose tissue often has unfavourable effects on systemic metabolism. In addition to non-alcoholic fatty liver disease, which has received considerable attention, pancreatic fat has become an important area of research throughout the past 10 years. While a number of diagnostic approaches are available to quantify pancreatic fat, multi-echo Dixon MRI is currently the most developed method. Initial studies have shown associations between pancreatic fat and the metabolic syndrome, impaired glucose metabolism and type 2 diabetes mellitus. Pancreatic fat is linked to reduced insulin secretion, at least under specific circumstances such as prediabetes, low BMI and increased genetic risk of type 2 diabetes mellitus. This Review summarizes the possible causes and metabolic consequences of pancreatic fat accumulation. In addition, potential therapeutic approaches for addressing pancreatic fat accumulation are discussed.