Since 1980 worldwide obesity has doubled in incidence to 52 % of people
being overweight or obese. Obesity causes various comorbidities such
as cardiovascular diseases, type II diabetes, dyslipidemia and several cancer
types, making it one of the biggest challenges in worldwide health care systems.
It is well known that obesity is highly heritable by either monogenetic
causes or multifactorial interactions of different genes that superimpose on
environmental factors and behavior. To answer questions in understanding
mechanisms of obesity and/or associated metabolic pathways, mouse models
have been a powerful tool. Several approaches in characterizing genes involved
in obesity development through mouse engineering have been implemented,
with the Cre/loxP system emerging as one of the most informative
and widespread techniques. Using this approach, promoter-dependent temporal
and tissue-specific regulated recombination can be achieved by Tamoxifen
administration. To investigate effects of Tamoxifen on adipocyte biology
in vivo, we characterized 12 weeks old male C57BL/6NTac mice after Tamoxifen
treatment. We found that Tamoxifen treatment caused transient body
composition changes, increased HbA1c, triglyceride and free fatty acid serum
concentrations as well as smaller adipocytes in combination with browning
of subcutaneous adipose tissue. Therefore, we suggest considering these effects
when using Tamoxifen as a tool to induce conditional transgenic mouse
models and to treat control mice in parallel. Another methodology used to
identify genes involved in obesity related traits is QTL mapping in combination
with congenic and subcongenic strains of mice or rats. One candidate
gene that was previously identified on rat chromosome 4 is replication initiator 1 (Repin1 ). This gene was first described as a 60 kDa zinc finger protein
involved in replication activation of the Chinese hamster dihydrofolate reductase
(dhfr ) gene. Moreover, a triplet repeat (TTT) in the 3’UTR is associated
with facets of the metabolic syndrome, including body weight, serum insulin,
cholesterol and triglyceride levels. In vitro studies in 3T3-L1 cells revealed
that Repin1 regulates adipocyte size, glucose transport and lipid metabolism.
In this thesis functional analyses of Repin1 were performed using different
Repin1 deficient mouse models. In the first study we generated a whole body
Repin1 deficient db/db double knockout mouse (Rep1−/−x db/db) and systematically
characterized the consequences of Repin1 deficiency. Our study
provided evidence that loss of Repin1 in db/db mice improves insulin sensitivity
and reduces chronic hyperglycemia most likely by reducing fat mass
and adipose tissue inflammation. We next generated a liver-specific Repin1
knockout mouse (LRep1−/−) and could show that loss of Repin1 in liver leads
to reduced body weight gain in combination with lower fat mass. Liver specific
Repin1 deficient mice also show lower triglyceride content in the liver,
improved insulin sensitivity and altered gene expression of genes involved
in lipid and glucose metabolism. Finally, we inactivated the Repin1 gene in
adipose tissue (iARep−/−) at an age of four weeks using Tamoxifen-inducible
gene targeting strategies on a background of C57BL/6NTac mice. Mice lacking
Repin1 in adipose tissue showed reduced body weight gain, decreased
fat mass with smaller adipocytes, improved insulin sensitivity, lower LDL-,
HDL- and total cholesterol serum concentrations and reduced expression of
genes involved in lipid metabolism (Cd36 and Lcn2 ). In conclusion, the thesis
presented here provides novel insights into Repin1 function. Moreover,
the data clearly indicate that Repin1 plays a role in insulin sensitivity and
lipid metabolism by regulating key genes involved in those pathways.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:16945 |
| Date | 03 January 2018 |
| Creators | Hesselbarth, Nico |
| Contributors | Universität Leipzig |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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