Periodic Report
1.
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PUBLISHABLE SUMMARY
Summary description of the project objectives
The ADDIO project aimed to unravel the impact of adipose DPP4 on impaired glucose
tolerance and insulin resistance in diet-induced obesity using a unique model of adiposespecific knockout of DPP4.
Figure 1. Schematic diagram depicting the experimental design of the project. Mice with deletion
of the DPP4 gene in AT were generated using the cre/loxP system under control of the aP2 promoter
on a C57BL/6J background. Body composition was analyzed every 4 weeks by NMR. ipGTT, ipITT
were assessed at week 20. Blood parameters and adipose tissue analysis were done at end point.
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Description of the work performed since the beginning of the project
The first year of project (2013-2014) comprised 2 initial work packages covering the 2 first
aims of the project (as described in the Annex I of the grant agreement). In the first work
package, we characterized the metabolic phenotype of adipose-specific DPP4 knockout mice
in diet-induced obesity. This included, besides comprehensive phenotyping in metabolic
cages, blood profiling, oGTT and hyperinsulinemic-euglycemic clamps. In a second work
package, we have studied the impact of adipose DPP4 on the development of insulin
resistance and adipocyte enlargement, comparing the effect of a high fat diet-induced obesity
on the development of adipose tissue inflammation in wild type and adipose-specific DPP4
knockout mice, respectively.
In the second period of the project (2014-2015) we have completed work package 3, aiming
to identify the mechanism responsible for the potential protective effects in adipose-specific
DPP4 knockout mice under high fat diet. We have analysed the secretory output of adipose
tissue explants from visceral and subcutaneous depots high-fat fed wild type vs. KO animals.
We have characterized the inflammatory status of AT by crown-like structures as an indicator
of macrophage infiltration.
 Description of the main results achieved so far
DPP4 expression in mature adipocytes from KO mice was significantly reduced up to 65 %
with unaffected expression in non-adipocyte cells within AT. Serum DPP4 was significantly
lower in KO animals on both diets. KO mice gained significantly more weight, fat and lean
mass on HFD. The genotype exerted no effect on energy expenditure, respiratory quotient
and spontaneous physical activity. At systemic level, both glucose and insulin tolerance
(assessed by intraperitoneal tests) and clamps were affected by HFD but not by the
genotype. However, other markers of insulin resistance such as fasting insulin and HOMA-IR
were significantly lower in KO mice on HFD. Cholesterol was reduced in both KO mice on
chow and on HFD compared to WT, but triglycerides were similar. In this line, triglyceride
content in the liver did not differ between the WT and KO animals.
Within adipose tissue, we observed that within the HFD group, the KO mice displayed a
marked shift in the adipocyte size distribution towards smaller adipocytes. This effect was
more dramatic in the subcutaneous fat compared to the visceral depot. AT inflammation
plays a pivotal role in the development of insulin resistance, therefore we assessed the
expression of the M2 anti-inflammatory macrophage markers vs. M1 pro-inflammatory
markers. In both fat depots, differentiation markers remained similar whereas the antiinflammatory M2 macrophage markers macrophage mannose receptor 1 and interleukin (IL)10 were significantly upregulated in KO animals in both depots compared to WT under HFD.
Nevertheless, in the visceral fat, the pro-inflammatory markers, IL-6 and monocyte
chemotactic protein-1 were significantly increased in KO mice compared to WT animals
under HFD. Macrophage infiltration in the AT was analyzed by counting galectin-3 positive
crown-like structures by immunostaining. Crown-like structures (CLS) are formed as a result
of macrophages infiltrating into AT to reabsorbe dead adipocytes. Under HFD, the KO
animals displayed significantly enhanced CLS in the visceral depot. Serum DPP4 correlated
significantly with adipocyte size in both subcutaneous and visceral fat, while negatively with
serum adiponectin.
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Final results and their potential impact and use
In conclusion, our model proves that AT is an important source of DPP4 in mice. The higher
increase in body weight and fat mass under HFD challenge observed in the KO animals, is
not followed by an increased impairment of glucose tolerance. Taken into account that KO
animals display smaller adipocytes under HFD, these findings point towards a beneficial role
for DPP4 deletion in adipose tissue remodeling during HFD, specifically within the
subcutaneous fat, where a more anti-inflammatory profile is observed under HFD (figure 2).
Nevertheless, future studies will help to clarify how DPP4 deletion in AT can be translated
into a more efficient protection against metabolic diseases. This is of special interest in the
case of obese type 2 diabetic patients currently treated with DPP4 inhibitors.
Figure 2. Schematic diagram depicting the main outcomes of the ADDIO project.
Contact details: eckel@uni-duesseldorf.de
http://ddz.uni-duesseldorf.de/de/forschung-am-ddz/paul-langerhans-gruppe-fuer-integrative
physiologie