Decreased GPIHBP1 protein levels in visceral adipose tissue partly underlie the hypertriglyceridemic phenotype in insulin resistance

Human visceral adipose tissue microvascular endothelial cell isolation and establishment of co-culture with white adipocytes to analyze cell-cell communication

Communication between adipocytes and endothelial cells (EC) is suggested to play an important role in the metabolic function of white adipose tissue. In order to generate tools to investigate in detail the physiology and communication of EC and adipocytes, a method for isolation of adipose microvascular EC from visceral adipose tissue (VAT) biopsies of subjects with obesity was developed. Moreover, mature white adipocytes were isolated from the VAT biopsies by a method adapted from a previously published Membrane aggregate adipocytes culture (MAAC) protocol. The identity and functionality of the cultivated and isolated adipose microvascular EC (AMvEC) was validated by imaging their morphology, analyses of mRNA expression, fluorescence activated cell sorting (FACS), immunostaining, low-density lipoprotein (LDL) uptake, and in vitro angiogenesis assays. Finally, we established a new trans filter co-culture system (membrane aggregate adipocyte and endothelial co-culture, MAAECC) for the analysis of communication between the two cell types. EC-adipocyte communication in this system was validated by omics analyses, revealing several altered proteins belonging to pathways such as metabolism, intracellular transport and signal transduction in adipocytes co-cultured with AMvEC. In reverse experiments, induction of several pathways including endothelial development and functions was found in AMvEC co-cultured with adipocytes. In conclusion, we developed a robust method to isolate EC from small quantities of human VAT. Furthermore, the MAAECC system established during the study enables one to study the communication between primary white adipocytes and EC or vice-versa and could also be employed for drug screening.

The evolving functions of the vasculature in regulating adipose tissue biology in health and obesity

Adipose tissue is an endocrine organ and a crucial regulator of energy storage and systemic metabolic homeostasis. Additionally, adipose tissue is a pivotal regulator of cardiovascular health and disease, mediated in part by the endocrine and paracrine secretion of several bioactive products, such as adipokines. Adipose vasculature has an instrumental role in the modulation of adipose tissue expansion, homeostasis and metabolism. The role of the adipose vasculature has been extensively explored in the context of obesity, which is recognized as a global health problem. Obesity-induced accumulation of fat, in combination with vascular rarefaction, promotes adipocyte dysfunction and induces oxidative stress, hypoxia and inflammation. It is now recognized that obesity-associated endothelial dysfunction often precedes the development of cardiovascular diseases. Investigations have revealed heterogeneity within the vascular niche and dynamic reciprocity between vascular and adipose cells, which can become dysregulated in obesity. Here we provide a comprehensive overview of the evolving functions of the vasculature in regulating adipose tissue biology in health and obesity.

Case Report: Successful Management of a 29-Day-Old Infant With Severe Hyperlipidemia From a Novel Homozygous Variant of GPIHBP1 Gene

BACKGROUND

Severe hyperlipidemia is characterized by markedly elevated blood triglyceride levels and severe early-onset cardiovascular diseases, pancreatitis, pancreatic necrosis or persistent multiple organ failure if left untreated. It is a rare autosomal recessive metabolic disorder originated from the variants of lipoprotein lipase gene, and previous studies have demonstrated that most cases with severe hyperlipidemia are closely related to the variants of some key genes for lipolysis, such as LPL, APOC2, APOA5, LMF1, and GPIHBP1. Meanwhile, other unidentified causes also exist and are equally worthy of attention.

METHODS

The 29-day-old infant was diagnosed with severe hyperlipidemia, registering a plasma triglyceride level as high as 25.46 mmol/L. Whole exome sequencing was conducted to explore the possible pathogenic gene variants for this patient.

RESULTS

The infant was put on a low-fat diet combined with pharmacological therapy, which was successful in restraining the level of serum triglyceride and total cholesterol to a low to medium range during the follow-ups. The patient was found to be a rare novel homozygous duplication variant-c.45_48dupGCGG (Pro17Alafs^*22) in GPIHBP1 gene-leading to a frameshift which failed to form the canonical termination codon TGA. The mutant messenger RNA should presumably produce a peptide consisting of 16 amino acids at the N-terminus, with 21 novel amino acids on the heels of the wild-type protein.

CONCLUSIONS

Our study expands on the spectrum of GPIHBP1 variants and contributes to a more comprehensive understanding of the genetic diagnosis, genetic counseling, and multimodality therapy of families with severe hyperlipidemia. Our experience gained in this study is also contributory to a deeper insight into severe hyperlipidemia and highlights the importance of molecular genetic tests.