Congenic BB.SHR (D4Mit6-Npy-Spr) rats: a new aid to dissect the genetics of obesity

Contribution of animal models to diabetes research: Its history, significance, and translation to humans

Diabetes mellitus is still expanding globally and is epidemic in developing countries. The combat of this plague has caused enormous economic and social burdens related to a lowered quality of life in people with diabetes. Despite recent significant improvements of life expectancy in patients with diabetes, there is still a need for efforts to elucidate the complexities and mechanisms of the disease processes to overcome this difficult disorder. To this end, the use of appropriate animal models in diabetes studies is invaluable for translation to humans and for the development of effective treatment. In this review, a variety of animal models of diabetes with spontaneous onset in particular will be introduced and discussed for their implication in diabetes research.

Histomorphometric and radiographical changes after lumbar implantation of the PEEK nonfusion interspinous device in the BB.4S rat model

STUDY DESIGN

An experimental animal study.

OBJECTIVE

To investigate histomorphometric and radiographical changes in the BB.4S rat model after PEEK (polyetheretherketone) nonfusion interspinous device implantation.

SUMMARY OF BACKGROUND DATA

Clinical effectiveness of the PEEK nonfusion spine implant Wallis (Abbott, Bordeaux, France; now Zimmer, Warsaw, IN) is well documented. However, there is a lack of evidence on the long-term effects of this implant on bone, in particular its influence on structural changes of bone elements of the lumbar spine.

METHODS

Twenty-four male BB.4S rats aged 11 weeks underwent surgery for implantation of a PEEK nonfusion interspinous device or for a sham procedure in 3 groups of 8 animals each: (1) implantation at level L4-L5; (2) implantation at level L5-L6; and (3) sham surgery. Eleven weeks postoperatively osteolyses at the implant-bone interface were measured via radiograph, bone mineral density of vertebral bodies was analyzed using osteodensitometry, and bone mineral content as well as resorption of the spinous processes were examined by histomorphometry. RESULTS.: Resorption of the spinous processes at the site of the interspinous implant was found in all treated segments. There was no significant difference in either bone density of vertebral bodies or histomorphometric structure of the spinous processes between adjacent vertebral bodies, between treated and untreated segments and between groups.

CONCLUSION

These findings indicate that resorption of spinous processes because of a result of implant loosening, inhibit the targeted load redistribution through the PEEK nonfusion interspinous device in the lumbar spinal segment of the rat. This leads to reduced long-term stability of the implant in the animal model. These results suggest that PEEK nonfusion interspinous devices like the Wallis implants may have time-limited effects and should only be used for specified indications.

Life or death? A physiogenomic approach to understand individual variation in responses to hemorrhagic shock

Severe hemorrhage due to trauma is a major cause of death throughout the world. It has often been observed that some victims are able to withstand hemorrhage better than others. For decades investigators have attempted to identify physiological mechanisms that distinguish survivors from nonsurvivors for the purpose of providing more informed therapies. As an alternative approach to address this issue, we have initiated a research program to identify genes and genetic mechanisms that contribute to this phenotype of survival time after controlled hemorrhage. From physiogenomic studies using inbred rat strains, we have demonstrated that this phenotype is a heritable quantitative trait, and is therefore a complex trait regulated by multiple genes. Our work continues to identify quantitative trait loci as well as potential epigenetic mechanisms that might influence survival time after severe hemorrhage. Our ultimate goal is to improve survival to traumatic hemorrhage and attendant shock via regulation of genetic mechanisms and to provide knowledge that will lead to genetically-informed personalized treatments.

Influence of glycemic control on tympanic membrane healing in diabetic rats

OBJECTIVES/HYPOTHESIS

It is generally assumed that glycemic control in diabetic patients is important in optimizing wound healing. The goal of this study was to examine tympanic membrane (TM) wound healing in spontaneously diabetic rats depending on the diabetic metabolic state compared to nondiabetic control animals.

STUDY DESIGN

Prospective controlled study in experimental animals.

METHODS

Right-sided myringotomy was performed in 20 normoglycemic rats, 17 well-compensated, and 23 poorly compensated diabetic rats. TMs were observed for a total of 3 weeks. Effect of diabetic metabolic state on the healing of the TMs was evaluated by closure rates and histology.

RESULTS

Diabetic rats showed a significant delay in TM wound healing compared to the control group, but there were no significant differences between both diabetes groups.

CONCLUSIONS

Glycemic control does not influence TM wound repair in an animal model of type 1 diabetes.

Transplantation of adipose tissue protects BB/OK rats from type 1 diabetes development

B(io) B(reedding)/O(ttawa) K(alsburg) rats spontaneously develop insulin-dependent type 1 diabetes. Days before BB/OK rats become diabetic, their body seems to be flabby which may be attributed to loss of subcutaneous fat. However, the rats are normoglycemic and manifest 3-4 days later. This observation prompted us to search for possibilities to avoid the loss of adipose tissue. BB/OK rats were subcutaneously grafted with visceral adipose tissue. In total, 34 (71%) out of 48 male and 23 (49%) out of 47 female BB/OK rats grafted with adipose tissue developed type 1 diabetes so that significantly more females than males were protected from diabetes development (p=0.03). In the control group, 17 (85%) out of 20 male and 20 (95%) out of 21 female BB/OK rats were diabetic. Adipose tissue transplantation can protect BB/OK rats from type 1 diabetes development in a sex specific manner. One could conclude that the manipulations have influenced fat accumulation and/or fat metabolism which prevent type 1 diabetes development in about 50% of BB/OK rats. This idea is supported by the finding that a mutation in the leptin receptor of NOD mice suppresses type 1 diabetes progression.

Triplet repeat in the Repin1 3'-untranslated region on rat chromosome 4 correlates with facets of the metabolic syndrome

BACKGROUND

Congenic and subcongenic rat strains confirmed the quantitative trait loci (QTLs) for facets of the metabolic syndrome between 60.53 and 77.11 Mb on chromosome 4. The analysis of candidate genes in this region favoured the replication initiator 1 (Repin1) characterized by a SNP in the coding region and a triplet repeat (TTT) in the 3'-untranslated region (3'UTR).

METHODS

We analysed nine rat strains (BB/OK, SHR, F344, BN, DA, LEW, hHTg, WOKW, and their founders WOK-F) and four wild rats on DNA (sequencing) and RNA level (gene expression in blood, liver, subcutaneous, and epididymal adipocytes). In addition, the rats were phenotypically characterized in order to link the rat phenotype to genotype differences in the QTL on chromosome 4.

RESULTS

Wild rats were heterozygous for the SNP (C/T), whereas all the inbred strains were homozygous. The shortest triplet repeat was found in SHR (5) and the highest was found in hHTg and WOKW (11), which developed metabolic disorders. The repeat number correlated with most phenotypic traits studied. Using linear multiple regression analysis with repeat size as the dependent variable and considering all the data of this study, it was clearly demonstrated that not only VLDL cholesterol and serum insulin but also the expression of Repin1 in the liver is significantly associated with the repeat size of the 3'UTR.

CONCLUSIONS

It is concluded that the triplet repeat expansion in 3'UTR is involved in metabolic alterations as found in hHTg and WOKW rats and that the functional unknown gene, Repin1, could be a novel candidate gene for the development of facets of the metabolic syndrome.

Reciprocal congenic lines for a major stroke QTL on rat chromosome 1

We previously identified a quantitative trait locus (QTL) for stroke proneness between the kallikrein (Klk) and Mt1pa markers on rat chromosome 1. To gain functional insights, we constructed congenic strains by introgressing either the whole or selected chromosomal segments from the stroke-prone (SHRsp) onto the stroke-resistant (SHRsr) spontaneously hypertensive rat genome and vice versa. The phenotype was the latency to develop stroke under a Japanese high-salt, low-potassium diet for 3 mo [known as Japanese diet (JD)]. Blood pressure (BP) was measured by tail cuff throughout the experiment. Urinary protein excretion was monitored in all lines under JD. The SHRsp-derived lines carrying the SHRsr allele, and particularly the D1Rat134-Mt1pa chromosomal segment, had a significant delay of stroke occurrence and improved survival compared with SHRsp (P < 0.001). On the other hand, a significant occurrence of stroke events (20%) was detected in the reciprocal lines by the end of the 3-mo treatment with JD (P = 0.003). The stroke phenotype was also associated with increased proteinuria. Our results underscore the functional importance of the Chr 1 stroke QTL. Furthermore, they underscore the utility of stroke/congenic lines in dissecting the genetics of stroke.

Is there an autoimmune process in bone? Gene expression studies in diabetic and nondiabetic BB rats as well as BB rat-related and -unrelated rat strains

It is well known that type 1 diabetes is associated with a decrease in bone mass and delayed healing of fractures in human and in animal models of type 1 diabetes. Using well- and poorly compensated diabetic BB/O(ttawa) K(arlsburg) rats spontaneously developing insulin-dependent type 1 diabetes, it was recently shown that, in contrast to all other tissues studied, bone is most influenced by metabolic state and seems to be regulated in a manner different from other organs. Therefore, we studied the expression of additional genes (Bmp-1, Bmp-4, Vegf, Bglap, Il-1b, Infg, Tnfa, Calca, Sp1, Yy1) in bone of nondiabetic BB rats compared with newly diagnosed and well- and poorly compensated diabetic rats as well as two nondiabetes-prone congenic BB.SHR rats, BB rat-related (WOKW) and -unrelated rat strains (F344). Six males of each group were euthanized, the tibial bone was removed, and total RNA was extracted, transcribed in complementary DNA, and used for real-time PCR. In a comparison of nondiabetic with diabetic groups, the relative gene expression was reduced by >80% in newly diagnosed and in well-compensated diabetic BB/OK rats. The gene expression in poorly compensated rats increased significantly in 7 of 10 genes and was comparable with those of nondiabetic BB/OK rats. In a comparison of gene expression between diabetes-prone BB/OK and nondiabetes-prone BB.1K, BB.4S, WOKW, and F344 rats, there were no significant differences between newly diagnosed and well-compensated BB/OK diabetic rats and nondiabetic BB.1K, BB.4S, WOKW, and F344 rats. On the basis of these findings, we concluded that spontaneous diabetes influences bone gene expression in BB/OK rats, which may be attributed to the genetically determined autoimmune process not only affecting pancreatic beta-cells but also bone formation and resorption.

Alleles on rat chromosome 4 (D4Got41-Fabp1/Tacr1) regulate subphenotypes of obesity

OBJECTIVE

The use of inbred animal models is an essential component of the genetic dissection of complex diseases. Because quantitative trait loci for serum triglycerides, total cholesterol, and body weight were mapped on chromosome 4 in a cross of BioBreeding/OttawaKarlsburg (BB/OK) and spontaneously hypertensive (SHR) rats, we established a congenic BB.SHR rat strain by introgressing a SHR segment of chromosome 4 (D4Got41-Tacr1) into a BB/OK background. The phenotype of these BB.SHR rats (BB.4S) confirmed the quantitative trait loci. To discover whether the phenotype of BB.4S can only be attributed to the SHR segment per se, we established an additional congenic BB.WOKW strain by introgressing a similar segment of chromosome 4 (D4Got41-Fabp1) of the Wistar Ottawa Karlsburg RT1(u) rat into a BB/OK background, termed briefly BB.4W.

RESEARCH METHODS AND PROCEDURES

Male normoglycemic BB/OK (20), BB.4S (20), and BB.4W (16) rats were longitudinally studied for body weight, serum triglycerides, total and high-density lipoprotein-cholesterol, and glucose tolerance. At the end of the observation period (32 weeks), serum insulin, leptin, and adiposity index (AI) were determined.

RESULTS AND DISCUSSION

Congenic BB.4S and BB.4W were significantly heavier, and AI, serum triglycerides, and total cholesterol values were significantly elevated in BB.4S and BB.4W compared with BB/OK but more pronounced in BB.4S. The highest serum insulin was found in BB.4W and highest leptin in BB.4S. Because the body weight gain and AI were comparable between BB.4S and BB.4W, the obviously higher insulin levels in BB.4W and higher leptin values in BB.4S suggest that the two congenics most probably define two subphenotypes of obesity and provide the unique opportunity to study their genetics.

Phenotypic and genetic analyses of subcongenic BB.SHR rat lines shorten the region on chromosome 4 bearing gene(s) for underlying facets of metabolic syndrome

Congenic BB.SHR ( D4Got41-Npy-Tacr1; BB.4S) rats develop an incomplete metabolic syndrome with obesity, hyperleptinemia, and dyslipidemia compared with their progenitor strain, the diabetes-prone BB/OK rat. To narrow down the underlying gene(s), two subcongenic BB.SHR rat lines, briefly termed BB.4Sa and BB.4Sb, were generated. Male BB.4S ( n = 20), BB.4Sa ( n = 24), and BB.4Sb ( n = 26) were longitudinally characterized for facets of the metabolic syndrome and analyzed for expression of genes located in the region of interest in liver and blood. Body weight gain was comparable, serum triglycerides and leptin were significantly increased, and total cholesterol and HDL-cholesterol ratio were decreased in BB.4S compared with both subcongenics. Serum insulin was significantly higher in BB.4S and BB.4Sa than in BB.4Sb. The adiposity index showed a graduated decrease from BB.6S to BB.4Sb. Obvious differences in relative expression were found in 6 of 10 genes in liver and in 2 of 9 genes in blood. Only one gene, the eukaryotic translation initiation factor 2α kinase 3 ( Eif2ak3 also called Perk or Pek), was significantly less expressed in liver and in blood of both subcongenic BB.4Sa and BB.4Sb compared with their “parental” BB.4S rats. Based on the phenotype and genotype in BB.4S and its subcongenic derivatives, the most important region on chromosome 4 can be said to lie between D4Got72 and Tacr1. Eif2ak3 is mapped in this region. Considering the function of Eif2ak3, it may be a candidate gene for the development of glucose intolerance found in both subcongenics but not in BB.4S. Allelic variants between BB/OK and SHR could influence Eif2ak3 function, possibly leading not only to glucose intolerance but also to the disturbances in hepatic and renal function found in human Wolcott-Rallison syndrome.