A history of obesity leaves an inflammatory fingerprint in liver and adipose tissue.

BACKGROUND/OBJECTIVES: Dieting is a popular yet often ineffective way to lower body weight, as the majority of people regain most of their pre-dieting weights in a relatively short time. The underlying molecular mechanisms driving weight regain and the increased risk for metabolic disease are still incompletely understood. Here we investigate the molecular alterations inherited from a history of obesity. METHODS: In our model, male high-fat diet (HFD)-fed obese C57BL/6J mice were switched to a low caloric chow diet, resulting in a decline of body weight to that of lean mice. We measured body composition, as well as metrics of glucose, insulin and lipid homeostasis. This was accompanied by histological and gene expression analysis of adipose tissue and liver to assess adipose tissue inflammation and hepatosteatosis. Moreover, acute hypothalamic response to (re-) exposure to HFD was assessed by qPCR. RESULTS & CONCLUSIONS: Within 7 weeks after diet switch, most obesity-associated phenotypes, such as body mass, glucose intolerance and blood metabolite levels were reversed. However, hepatic inflammation, hepatic steatosis as well as hypertrophy and inflammation of perigonadal, but not subcutaneous, adipocytes persisted in formerly obese mice. Transcriptional profiling of liver and perigonadal fat revealed an upregulation of pathways associated with immune function and cellularity. Thus, we show that weight reduction leaves signs of inflammation in liver and perigonadal fat, indicating that persisting proinflammatory signals in liver and adipose tissue could contribute to an increased risk of formerly obese subjects to develop the metabolic syndrome upon recurring weight gain.

Insulin resistance in vascular endothelial cells promotes intestinal tumour formation.

The risk of several cancers, including colorectal cancer, is increased in patients with obesity and type 2 diabetes, conditions characterised by hyperinsulinaemia and insulin resistance. Because hyperinsulinaemia itself is an independent risk factor for cancer development, we examined tissue-specific insulin action in intestinal tumour formation. In vitro, insulin increased proliferation of intestinal tumour epithelial cells by almost two-fold in primary culture of tumour cells from ApcMin/+ mice. Surprisingly, targeted deletion of insulin receptors in intestinal epithelial cells in ApcMin/+ mice did not change intestinal tumour number or size distribution on either a low or high-fat diet. We therefore asked whether cells in the tumour stroma might explain the association between tumour formation and insulin resistance. To this end, we generated ApcMin/+ mice with loss of insulin receptors in vascular endothelial cells. Strikingly, these mice had 42% more intestinal tumours than controls, no change in tumour angiogenesis, but increased expression of vascular cell adhesion molecule-1 (VCAM-1) in primary culture of tumour endothelial cells. Insulin decreased VCAM-1 expression and leukocyte adhesion in quiescent tumour endothelial cells with intact insulin receptors and partly prevented increases in VCAM-1 and leukocyte adhesion after treatment with tumour necrosis factor-α. Knockout of insulin receptors in endothelial cells also increased leukocyte adhesion in mesenteric venules and increased the frequency of neutrophils in tumours. We conclude that although insulin is mitogenic for intestinal tumour cells in vitro, impaired insulin action in the tumour microenvironment may be more important in conditions where hyperinsulinaemia is secondary to insulin resistance. Insulin resistance in tumour endothelial cells produces an activated, proinflammatory state that promotes tumorigenesis. Improvement of endothelial dysfunction may reduce colorectal cancer risk in patients with obesity and type 2 diabetes.

C-terminally truncated kindlin-1 leads to abnormal adhesion and migration of keratinocytes.

BACKGROUND: The Kindler syndrome (KS) protein kindlin-1 is a member of a protein complex that links cortical actin to integrins on the surface of basal keratinocytes. Loss of kindlin-1 leads to abnormalities of cell adhesion and motility, and to skin blistering and progressive poikiloderma as clinical symptoms. OBJECTIVES: Here we investigated a severely affected patient, disclosed the mutation that caused the disease and delineated its biological consequences. METHODS: Mutation screening of the kindlin-1 gene, KIND1 (now called FERMT1), was performed with polymerase chain reaction (PCR) amplification of all exons and sequencing. Mutated kindlin-1 was characterized by reverse transcriptase (RT)-PCR and immunoblotting, and genotype-phenotype correlations were analysed using immunohistochemical staining of skin biopsies and keratinocytes from the patient's skin. Cell adhesion and motility were assessed with functional tests. RESULTS: We disclosed a splice site mutation in the first position of intron 13 of the FERMT1 gene, which caused skipping of exon 13. The short transcript partially escaped nonsense-mediated mRNA decay and was translated into a truncated protein. CONCLUSION: A C-terminally truncated kindlin-1 in keratinocytes could not function correctly even if it were expressed.

Colocalization of kindlin-1, kindlin-2, and migfilin at keratinocyte focal adhesion and relevance to the pathophysiology of Kindler syndrome.

Kindler syndrome (KS) results from pathogenic loss-of-function mutations in the KIND1 gene, which encodes kindlin-1, a focal adhesion and actin cytoskeleton-related protein. How and why abnormalities in kindlin-1 disrupt keratinocyte cell biology in KS, however, is not yet known. In this study, we identified two previously unreported binding proteins of kindlin-1: kindlin-2 and migfilin. Co-immunoprecipitation and confocal microscopy studies show that these three proteins bind to each other and colocalize at focal adhesion in HaCaT cells and normal human keratinocytes. Moreover, loss-of-function mutations in KIND1 result in marked variability in kindlin-1 immunolabeling in KS skin, which is mirrored by similar changes in kindlin-2 and migfilin immunoreactivity. Kindlin-1, however, may function independently of kindlin-2 and migfilin, as loss of kindlin-1 expression in HaCaT keratinocytes by RNA interference and in KS keratinocytes does not affect KIND2 or FBLIM1 (migfilin) gene expression or kindlin-2 and migfilin protein localization. In addition to identifying protein-binding partners for kindlin-1, this study also highlights that KIND1 gene expression and kindlin-1 protein labeling are not always reduced in KS, findings that are relevant to the accurate laboratory diagnosis of this genodermatosis by skin immunohistochemistry.