Regulation of Lipolysis in Adipose Tissue and Clinical Significance

The Molecular Basis and Therapeutic Potential of Leukemia Inhibitory Factor in Cancer Cachexia

Simple Summary

The mechanism of cancer cachexia is linked to a variety of factors, and inflammatory factors are thought to play a key role. We summarize the main roles of LIF in the development of cancer cachexia, including promoting fat loss, inducing skeletal muscle atrophy and causing anorexia nervosa. The main aim of this review is to increase the understanding of the effects of LIF in cachexia and to provide new insights into the treatment of cancer cachexia.

Abstract

Cachexia is a chronic metabolic syndrome that is characterized by sustained weight and muscle mass loss and anorexia. Cachexia can be secondary to a variety of diseases and affects the prognosis of patients significantly. The increase in inflammatory cytokines in plasma is deeply related to the occurrence of cachexia. As a member of the IL-6 cytokine family, leukemia inhibitory factor (LIF) exerts multiple biological functions. LIF is over-expressed in the cancer cells and stromal cells of various tumors, promoting the malignant development of tumors via the autocrine and paracrine systems. Intriguingly, increasing studies have confirmed that LIF contributes to the progression of cachexia, especially in patients with metastatic tumors. This review combines all of the evidence to summarize the mechanism of LIF-induced cachexia from the following four aspects: (i) LIF and cancer-associated cachexia, (ii) LIF and alterations of adipose tissue in cachexia, (iii) LIF and anorexia nervosa in cachexia, and (iv) LIF and muscle atrophy in cachexia. Considering the complex mechanisms in cachexia, we also focus on the interactions between LIF and other key cytokines in cachexia and existing therapeutics targeting LIF.

Human adipose tissue gene expression of solute carrier family 19 member 3 (SLC19A3); relation to obesity and weight-loss

OBJECTIVE

Adipose tissue is a specialized endocrine organ that is involved in modulating whole-body energy homeostasis and expresses a specific subset of genes, which may play a role in adipose tissue metabolism. The aim of this study was to search for novel adipose tissue-specific genes using a tissue panel of RNAseq expression profiles.

METHODS

RNAseq expression profiles from 53 human tissues were downloaded from the GTex database. SLC19A3 expression was analyzed by microarray or real-time PCR in two sets of paired subcutaneous and omental adipose tissue samples, in two studies with adipose tissue from persons with high or low body mass index (BMI), in adipose tissue from patients who underwent weight loss with a very-low caloric diet and during preadipocyte-adipocyte differentiation.

RESULTS

The RNAseq-based tissue distribution expression screen identified SLC19A3 (encoding the thiamine transporter 2) as adipose tissue-specific. SLC19A3 expression was higher in subcutaneous compared with omental adipose tissue in both sample sets (p = 0.043 and p < 0.001). Preadipocyte differentiation towards adipocytes resulted in increased SLC19A3 gene expression (p = 0.018 or less at all-time points). Subcutaneous adipose tissue expression of SLC19A3 was lower in persons with high BMI in both cohorts (p = 0.008, and p < 0.001) and increased during a weight-loss intervention (p = 0.006).

CONCLUSION

The specific adipose tissue expression pattern of SLC19A3, together with its regulation in obesity and during weight loss, indicate that it plays a key role in adipocyte metabolism.

Circulating lipids in men with type 2 diabetes following 3 days on a carbohydrate-free diet versus 3 days of fasting

OBJECTIVE

We have been interested in determining the effects of dietary changes on fuel metabolism and regulation in men with type 2 diabetes mellitus (T2DM). In this study, the changes in 24-hr circulating lipid profiles were determined when the major fuel source was endogenous versus exogenous fat.

METHODS

Seven males with T2DM were randomized in a crossover design with a 4-week washout period. A standard mixed (control) diet (30%fat:15%protein:55%carbohydrate) was provided initially. Subsequently, a 72-hr (3-day) fast, or a high fat (85%), 15% protein, essentially carbohydrate-free (CHO-free) diet was provided for 72 hr. Triacylglycerol (TAG), non-esterified fatty acids (NEFA), β-hydroxybutyrate (bHB), and insulin-like growth factor-binding protein-1 (IGFBP-1) profiles were determined during the last 24 hr of intervention, as well as during the control diet.

RESULTS

Regardless of the amount of dietary fat (30% vs 85%) and differences in 24-hr profiles, TAG, NEFA, and bHB all returned to the previous basal concentrations within 24 hr. TAGs and NEFAs changed only modestly with fasting; bHB was elevated and increasing. The IGFBP-1 profile was essentially unchanged with either diet but increased with fasting.

CONCLUSION

A CHO-free diet resulted in a large increase in TAG and NEFA versus the control diet; however, both were cleared by the following morning. A negative NEFA profile occurred with the control diet. Thus, mechanisms are present to restore lipid concentrations to their original AM concentrations daily. Fasting resulted in stable concentrations, except for a continuing increase in bHB. Glucose and insulin, common fuel regulators, could not explain the results.