Animal Models

MCK-PPARalpha Transgenic Mice
Model of Skeletal Muscle Insulin Resistance

Background:
The peroxisome proliferator-activated receptor (PPAR) family of lipid-activated nuclear receptors serves a critical role in the gene regulatory control of cellular lipid metabolic pathways. In skeletal muscle, PPARalpha and PPARbeta/delta are expressed at relatively abundant levels and activate multiple cellular fatty acid uptake and utilization pathways. There is evidence that points to a role for the PPARalpha regulatory pathway in the lipid metabolic derangements related to obesity and diabetes.

Description of Mouse Model:
This mouse (MCK-PPARalpha), overexpresses PPARalpha driven by the skeletal muscle-specific creatine kinase promoter (MCK). Transgenic mice developed glucose tolerance despite being protected from diet-induced obesity. In skeletal muscle, the MCK-PPARalpha mice exhibited increased fatty acid oxidation rates, diminished AMP-activated protein kinase activity, and reduced insulin-stimulated glucose uptake without alterations in the phosphorylation status of key insulin-signaling proteins.

Figure (above): 
(Top) The schematic depicts the MCK-PPARalpha construct used for transgene production and autoradiographs demonstrating relative PPARalpha transgene mRNA (left) and protein (right) expression in gastrocnemius muscle of nontransgenic (NTG) and three lines of transgenic mice. PPARalpha transgene mRNA expression in various tissues of MCK-PPARalpha HE mice (bottom left). FLAG-PPARalpha protein levels in gastrocnemius of LE and ME MCK-PPARalpha mice compared to endogenous PPARalpha levels in liver and soleus of NTG mice (bottom right).

Publications:
Cell Metab. 2005 Feb;1(2):133-44.

 


MHC-PPARalpha Transgenic Mice
Model of Lipotoxic Diabetic Cardiomyopathy

Background:
Cardiac fatty acid and utilization pathways are controlled, at least in part, at the gene regulatory level. Studies have demonstrated an important role for the nuclear receptor peroxisome proliferator activated receptor alpha (PPARalpha) in the transcriptional control of genes involved in cardiac fatty acid uptake and oxidation. Although little is known about the pathogenesis of diabetic cardiomyopathy, evidence suggests that it is related to derangements in myocardial energy metabolism.

Description of Mouse Model:
This mouse (MHC-PPARalpha), overexpresses PPARalpha in a cardiac-specific manner driven by the alpha myosin heavy chain promoter (MHC). The expression of PPAR alpha target genes involved in cardiac fatty acid uptake and oxidation pathways was increased in the MHC-PPAR mice. In addition, the expressin of genes involved in glucose transport and utilization was reciprocally repressed in the transgenic hearts. Myocardial fatty acid oxidation rates were also increased and glucose uptake and oxidation was decreased in MHC-PPARalpha mice, a metabolic phenotype striking to the diabetic heart. MHC-PPARalpha mouse hearts exhibited signatures of diabetic cardiomyopathy including ventricular hypertrophy, activation of gene markers of pathologic growth, and transgenic expression-dependent alterations in systolic ventricular function.

Figure 1 (above):
Increased expression of PPARalpha target genes in hearts of transgenic mouse lines (MHC-PPAR mice) that express PPARalpha in a cardiac-restricted manner. Representative autoradiographs of Northern (top) and Western (middle) blot studies performed with heart samples from 6-week-old mice from four independent MHC-PPAR lines. At the exposure shown, endogenous PPARalpha could not be detected in NTG samples. FLAG-PPARalpha protein was detected in the transgenic mice using an antibody directed against either PPARalpha or FLAG. Cardiac-specific expression of FLAG-PPARalpha mRNA was confirmed by Northern blot analysis performed with multiple tissues (bottom panel represents the 402-2 line). H, heart; BAT, brown adipose tissue; SM, skeletal muscle; K, kidney; L, liver.

Figure 2 (left):
Myocardial lipid accumulation in fasted MHC-PPAR mice. (a) Photomicrographs depicting the histologic appearance of ventricular tissue from NTG and MHC-PPAR mice following a 24-hour fast at low (upper panels) and high (lower panels) magnification. Frozen tissue sections were stained with oil red O. Red droplets indicate neutral lipid staining. (b) Lipid profile of mouse ventricle samples prepared from MHC-PPAR or NTG mice given ad libitum access to food or fasted for 24 hours. Lipid species were separated and analyzed using ESIMS. Mass/charge (m/z) ratios of 814, 840, and 864 denote TAGs containing fatty acyl groups containing chain lengths of 16:0/16:0/16:0, 16:0/16:0/18:1, and 16:0/18:1/18:2, as shown at the top. (c) Representative autoradiographs of Northern blot analyses performed with total RNA isolated from cardiac ventricle of mice fed ad libitum or after a 24-hour fast using cDNA probes for diacylglyceride acyltransferase (DGAT), glycerol-3-phosphate acyltransferase (GPAT), and adipophilin. Ethidium bromide-stained 28S rRNA is shown as a control for loading.

 

 Publications:
J Clin Invest. 2002 Jan;109(1):121-30.
Proc Natl Acad Sci U S A. 2003 Feb 4;100(3):1226-31. Epub 2003 Jan 27.
Am J Physiol Heart Circ Physiol. 2006 Jan;290(1):H87-95. Epub 2005 Sep 9.

 


PGC-1alpha Deficient Mice

PGC-1alpha deficient mice

 

Figure (left): PGC-1-alpha deficient mice can't maintain the pace on a treadmill.

Background:
PGC-1alpha (peroxisome proliferator-activated receptor (PPAR) alpha coactivator-1alpha), a transcriptional coactivator, interacts with and coactivates a number of nuclear transcription factors. PGC-1alpha activates transcription factors involved in metabolic processes such as cellular energy metabolism and mitochondrial biogenesis, and thus it is not surprising that PGC-1alpha expression coincides with highly metabolic tissues. Moreover, dysregulation of PGC-1alpha has been implicated in various disorders including obesity, diabetes, and heart failure.

Description of Mouse Model:
PGC-1alpha deficient mice were generated by insertion/homologous recombination in embryonic stems cells creating an additional exon 3 between exon 5 and 6. PGC-1alpha deficient mice, although viable, exhibit abnormalities in energy metabolism leading to a multitude of defects in various organs. Defects include increased body fat, decreased mass of the heart and slow-twitch skeletal muscle, reduced muscle performance and exercise capacity, and developed hepatic steatosis after periods of fasting. In addition, PGC-1alpha deficient mice exhibit difficulties in maintaining body temperature under cold conditions, a slight reduction in their ability to control heart rate, and vacuolar lesions in the central nervous system. Importantly, most of the gross physiologic phenotypic manifestations of the PGC-1 a -deficient mice occur only in the context of a physiologic stress such as fasting or exercise. The general phenotype of PGC-1alpha deficient mice suggests the importance of PGC-1alpha in responding to the overall energy needs of the animals.

Publication:
PLoS Biol. 2005 Apr;3(4):e101. Epub 2005 Mar 15

Link to publication:
http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0030101

Link to Phenotypic allele description:
http://www.informatics.jax.org/javawi2/servlet/WIFetch?page=alleleDetail&key=34782


TRE-PGC1alpha x MHC-rtTA Mice
Transgenic Model for Cardiac-Specific Inducible PGC-1alpha Overexpression

Background:
PGC-1alpha (peroxisome proliferator-activated receptor (PPAR) alpha coactivator-1alpha), a transcriptional coactivator, interacts with and coactivates a number of nuclear transcription factors. PGC-1alpha activates transcription factors involved in metabolic processes such as cellular energy metabolism and mitochondrial biogenesis, and thus it is not surprising that PGC-1alpha expression coincides with highly metabolic tissues. Moreover, dysregulation of PGC-1alpha has been implicated in various disorders including obesity, diabetes, and heart failure.

Description of mouse model:
This mouse (TRE-PGC mice), when crossed with the MHC-rtTA mouse, overexpresses PGC-1 in a cardiac-specific manner. The MHC-rtTA mouse overexpresses the reverse tetracycline transactivator (rtTA) driven by the cardiac-specific alpha myosin heavy chain promoter (MHC-rtTA mice). Thus, PGC-1alpha overexpression can be induced in postnatal cardiac tissue with the addition of doxycycline to the drinking water or chow of TRE-PGC x MHC-rtTA mice.

Cardiac-specific overexpression of PGC-1alpha manifests as a robust increase in the number and size of mitochondria in the neonatal heart. In contrast, while adult TRE-PGC x MHC-rtTA mice exhibit only a minor increase in mitochondria number, they display abnormalities in mitochondrial ultrastructure and develop cardiomyopathy. The basis for the cardiomyopathy is unknown but likely involves uncontrolled mitochondrial proliferation and a reduction in expression of sarcomeric proteins. Removal of doxycycline from adult TRE-PGC x MHC-rtTA mice completely reverses the cardiomyophathic phenotype.

Publication:
Circ Res. 2004 Mar 5;94(4):525-33.
The MHC-rtTA mice were contributed by John McDonald and Maria Valencik John.mcdonald@hsc.utah.edu and Mvalen@unr.edu