Correlation of glycemic regulation and endotrophin in patients with type 2 Diabetes; pilot study

Instrumental variable and colocalization analyses identify endotrophin and HTRA1 as potential therapeutic targets for coronary artery disease

Coronary artery disease (CAD) remains a leading cause of disease burden globally, and there is a persistent need for new therapeutic targets. Instrumental variable (IV) and genetic colocalization analyses can help identify novel therapeutic targets for human disease by nominating causal genes in genome-wide association study (GWAS) loci. We conducted cis-IV analyses for 20,125 genes and 1,746 plasma proteins with CAD using molecular trait quantitative trait loci variant (QTLs) data from three different studies. 19 proteins and 119 genes were significantly associated with CAD risk by IV analyses and demonstrated evidence of genetic colocalization. Notably, our analyses validated well-established targets such as PCSK9 and ANGPTL4 while also identifying HTRA1 and endotrophin (a cleavage product of COL6A3) as proteins whose levels are causally associated with CAD risk. Further experimental studies are needed to confirm the causal role of the genes and proteins identified through our multiomic cis-IV analyses on human disease.

Endotrophin, a Key Marker and Driver for Fibroinflammatory Disease

Our overview covers several key areas related to recent results obtained for collagen type VI and endotrophin (ETP). (1) An introduction to the history of ETP, including how it was identified, how it is released, and its function and potential receptors. (2) An introduction to the collagen family, with a focus on what differentiates collagen type VI from an evolutionary standpoint. (3) An overview of collagen type VI, the 6 individual chains (COL6A1, A2, A3, A4, A5, and A6), their differences and similarities, as well as their expression profiles and function. (4) A detailed analysis of COL6A3, including the cleaved product endotrophin, and what separates it from the other 5 collagen 6 molecules, including its suggested function based on insights gained from knockout and gain of function mouse models. (5) The pathology of ETP. What leads to its presence and release and what are the consequences thereof? (6) Functional implications of circulating ETP. Here we review the data with the functional roles of ETP in mind. (7) We propose that ETP is a mediator for fibrotic (or fibroinflammatory) disorders. Based on what we know about ETP, we have to consider it as a target for the treatment of fibrotic (or fibroinflammatory) disorders. What segment(s) of the patient population would most dramatically respond to an ETP-targeted intervention? How can we find the population that would profit most from an intervention? We aim to present a broad overview over the ETP field at large, providing an assessment of where the future research efforts need to be placed to tap into the vast potential of ETP, both as a marker and as a target in different diseases.

Collagens Regulating Adipose Tissue Formation and Functions

The globally increasing prevalence of obesity is associated with the development of metabolic diseases such as type 2 diabetes, dyslipidemia, and fatty liver. Excess adipose tissue (AT) often leads to its malfunction and to a systemic metabolic dysfunction because, in addition to storing lipids, AT is an active endocrine system. Adipocytes are embedded in a unique extracellular matrix (ECM), which provides structural support to the cells as well as participating in the regulation of their functions, such as proliferation and differentiation. Adipocytes have a thin pericellular layer of a specialized ECM, referred to as the basement membrane (BM), which is an important functional unit that lies between cells and tissue stroma. Collagens form a major group of proteins in the ECM, and some of them, especially the BM-associated collagens, support AT functions and participate in the regulation of adipocyte differentiation. In pathological conditions such as obesity, AT often proceeds to fibrosis, characterized by the accumulation of large collagen bundles, which disturbs the natural functions of the AT. In this review, we summarize the current knowledge on the vertebrate collagens that are important for AT development and function and include basic information on some other important ECM components, principally fibronectin, of the AT. We also briefly discuss the function of AT collagens in certain metabolic diseases in which they have been shown to play central roles.

Extracellular Matrix (ECM) and Fibrosis in Adipose Tissue: Overview and Perspectives

Fibrosis in adipose tissue is a major driver of obesity-related metabolic dysregulation. It is characterized by an overaccumulation of extracellular matrix (ECM) during unhealthy expansion of adipose tissue in response to over nutrition. In obese adipose-depots, hypoxia stimulates multiple pro-fibrotic signaling pathways in different cell populations, thereby inducing the overproduction of the ECM components, including collagens, noncollagenous proteins, and additional enzymatic components of ECM synthesis. As a consequence, local fibrosis develops. The result of fibrosis-induced mechanical stress not only triggers cell necrosis and inflammation locally in adipose tissue but also leads to system-wide lipotoxicity and insulin resistance. A better understanding of the mechanisms underlying the obesity-induced fibrosis will help design therapeutic approaches to reduce or reverse the pathological changes associated with obese adipose tissue. Here, we aim to summarize the major advances in the field, which include newly identified fibrotic factors, cell populations that contribute to the fibrosis in adipose tissue, as well as novel mechanisms underlying the development of fibrosis. We further discuss the potential therapeutic strategies to target fibrosis in adipose tissue for the treatment of obesity-linked metabolic diseases and cancer. © 2023 American Physiological Society. Compr Physiol 13:4387-4407, 2023.

Extracellular matrix remodeling facilitates obesity-associated cancer progression

Obesity, a global public health concern, is an important risk factor for metabolic diseases and several cancers. Fibro-inflammation in adipose tissues (ATs) is tightly associated with the pathologies of obesity; excessive or uncontrolled extracellular matrix (ECM) production in AT has a crucial role in this pathogenesis. The ECM is a critical and functional component of various tissues, providing a mechanical and chemical network of proteins that controls cell survival, development, and tissue repair. The ECM is tightly regulated and dynamically remodeled; this is an important factor for AT expansion and can result in modifications to the physical shape and biological function of AT. Here, we focus on ECM remodeling in AT and how it affects obesity-related cancer progression.

Adipose Tissue Extracellular Matrix Remodeling in Response to Dietary Patterns and Exercise: Molecular Landscape, Mechanistic Insights, and Therapeutic Approaches

Simple Summary

Adipose tissue is considered a metabolic organ that adjusts overall energy homeostasis and critical hormones to the body’s needs. In conditions of caloric intake surpassing energy expenditure, lipid accumulation occurs with constant extracellular matrix deposition. Excess lipids and adipocyte hypertrophy may reduce extracellular matrix flexibility in conjunction with hypoxia and inflammation. These processes induce the development of adipose tissue fibrosis and correlated metabolic dysfunctions, such as insulin resistance. With the increasing rate of chronic diseases worldwide, it is essential to generate a more precise knowledge of fibrotic processes, as well as to create optimal models to study potential therapies to combat the harmful effects of extracellular matrix deposition. In this work, we focused on the physiological processes in the remodeling of adipose tissue fibrosis, along with their relevance to clinical indications. Furthermore, we emphasize understanding how lifestyle can alleviate adipocyte dysfunction. Several studies showed that a nutritionally balanced diet combined with exercise is a remarkable potential strategy for lipolytic activity, preventing rapid extracellular matrix expansion in parallel with insulin and glucose action improvements. Thus, the emerging beneficial role of exercise training and low-calorie diet on adipose tissue ECM remodeling is a topic that deserves attention from health professionals.

Abstract

The extracellular matrix (ECM) is a 3-dimensional network of molecules that play a central role in differentiation, migration, and survival for maintaining normal homeostasis. It seems that ECM remodeling is required for adipose tissue expansion. Despite evidence indicating that ECM is an essential component of tissue physiology, adipose tissue ECM has received limited attention. Hence, there is great interest in approaches to neutralize the harmful effects of ECM enlargement. This review compiles and discusses the current literature on adipose tissue ECM remodeling in response to different dietary patterns and exercise training. High-calorie diets result in substantial adipose tissue ECM remodeling, which in turn could lead to fibrosis (excess deposition of collagens, elastin, and fibronectin), inflammation, and the onset of metabolic dysfunction. However, combining a nutritionally balanced diet with exercise is a remarkable potential strategy for lipolytic activity, preventing rapid ECM expansion in different adipose tissue depots. Despite the distinct exercise modalities (aerobic or resistance exercise) reversing adipose tissue fibrosis in animal models, the beneficial effect on humans remains controversial. Defining molecular pathways and specific mechanisms that mediate the positive effects on adipose tissue, ECM is essential in developing optimized interventions to improve health and clinical outcomes.

Endotrophin is associated with chronic multimorbidity and all-cause mortality in a cohort of elderly women

BACKGROUND

The signalling peptide endotrophin is derived through proteolytic cleavage of the carboxyl-terminal during formation of type VI collagen. It is expressed by most descendants of the mesenchymal stem cells lineage, including adipocytes and fibroblasts, and have been proposed to be a central extracellular matrix hormone associated with several age-related diseases. We aimed to assess the association of endotrophin with chronic disease incidence and death in older women.

METHODS

5,602 elderly Danish women from the observational, prospective cohort: The Prospective Epidemiological Risk Factor (PERF) study were included in the analysis which covered baseline (BL) and follow-up (FU) 14 years later. An elastic net was used to investigate the relative importance of 58 variables to serum endotrophin-levels. 20 chronic diseases were defined on the basis of clinical variables available along with diagnoses extracted from both the National Patient Register, the National Diabetes Register and the Danish Cancer Registry. The cross-sectional associations between endotrophin-levels and these 17 chronic age-related diseases were investigated using logistic regression and a set-analysis explored disease-combinations within multimorbidity. The association of endotrophin with mortality was assessed by Cox proportional hazard models.

FINDINGS

Formation of type III collagen (PRO-C3), age and creatine-levels were the most influential variables of endotrophin-levels. Several chronic diseases were significantly associated with endotrophin-levels independent of age and BMI including chronic kidney disease (BL OR=3.7, p < 0.001; FU OR = 7.9 p < 0.001), diabetes (BL OR = 1.5, p = 0.0015, FU OR=1.6, p = 0.004) and peripheral arterial disease (BL OR = 1.3, p = 0.029; FU OR=2.4, p < 0.001). Lastly, endotrophin-levels were significantly rising with number of morbidities (p < 0.001) and a predictor of death after adjusting for age and BMI (BL HR=1.95; FU HR = 2.00).

INTERPRETATION

Endotrophin was associated with death and increased with number of morbidities. Endotrophin may be a central hormone of fibroblast that warrant investigation and possible targeted intervention in several chronic diseases.

FUNDING

The funder of the PERF study had no role in study design, data collection, data analysis, data interpretation, or writing of the report. The corresponding author had full access to all the data in the study and had final responsibility for the decision to submit for publication.