- Email: [email protected]
Influence of genetic predisposition to diabetes and obesity on mitochondrial function
BIOCHEMICAL
MEDICINE
Influence
KENNETH
AND
METABOLIC
BIOLOGY
35, 72-76 (1986)
of Genetic Predisposition to Diabetes and Obesity on Mitochondrial Function S. ROGERS,EDWIN S. HIGGINS, AND ROGERM. LORIA
Departments of Biochemistry, Microbiology and Immunology, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298 Received December 11, 1984
The importance of the mitochondrion in diabetes mellitus has been somewhat clouded by the diverse results obtained when diabetes was experimentally produced by drugs. For example, Parks et al. (1) reported that hepatic mitochondria were not affected in their uptake of inorganic phosphate or oxygen when organelles were obtained from rats treated with alloxan. On the other hand, Hall et al. (2) reported that rats treated with alloxan had hepatic mitochondria that were deficient in their ability to synthesize ATP. Mackerer e? al. (3) showed that alloxan and streptozotocin potentiated the efficiency with which rat liver mitochondria phosphorylated ADP by stimulating respiratory control without affecting P: 0 ratios. DiMarco and Hoppel (4) said that streptozotocin did not affect either mitochondrial protein content per gram of rat liver or mitochondrial respiratory control in their experiments. Neel (5) linked both the dietary and hereditary components of ,obesity and diabetes mellitus under the “thrifty genotype” hypothesis which states that certain gene(s) or mutation(s) may be favorable when food supply is limited but unfavorable when food is in abundance. The homozygous mutant mice C57BL/KsJ db + /db + and C57BL/6J ob/ob are hyperphagic, obese, and diabetic (6). These animals can maintain a normal body weight or increase their body fat even when their dietary intake is restricted from one-half to two-thirds of the amount of food intake by normal mice; i.e., 4 g/day may be lowered to 2 g/day (7- 9). We have used the inbred diabetic mutant mice, db+ /db+ , and the obese mutant mice, ob/ob, rather than chemically induced diabetes, as a model to study the influences of hyperphagia, obesity, and diabetes on respiratory control of liver mitochondria. Our results show that the spontaneous homozygous mutations, diabetes db+ /db+ , and obese, ob/ob, exert a significant influence on liver mitochondrial respiratory properties. MATERIALS AND METHODS
Inbred C57BL/6J mice with the homozygous diabetic mutation, db +/db +, the doubly heterozygous mutation, db + /+ m, or the homozygous mutation, 72 0885-4505/86 $3.00 Copyright All rights
0 1986 by Academic Press, Inc. of reproduction in any form reserved.
MITOCHONDRIA
OF DIABETIC
AND OBESE MICE
13
+ m/ + m, on this inbred genetic background were used as one group. On this genetic background the db+/db+ mutation results in hyperphagia, obesity, hyperglycemia, and spontaneous diabetes. The doubly heterozygote db + / + m is not hyperphagic, is not obese, and does not develop spontaneous diabetes. The homozygote, misty coat color mutant, + m/ + m, is lean and does not develop diabetes. The second group of experimental animals included the homozygous obese C57BL/6J ob/ob mutant and its inbred C57BL/6J +/ + control. The homozygous ob/ob is also hyperphagic, is obese, and develops a spontaneous diabetes-like disease. However, in the obese mutant, hyperinsulinemia is markedly higher than in the diabetic mutant db, and uncontrolled hyperglycemia and destruction of islet cells, which occurs in the diabetic db mutant, are not observed (10). Male mice 6 weeks old were purchased from the Jackson Laboratories (Bar Harbor, Maine). Mice were individually caged and placed on a light regime of 12 hr on/12 hr off. Water was provided ad libitum to all animals. To limit the effects of hyperphagia and obesity, db+/db+ and ob/ob mice were fed 2 g/day Purina Laboratory Mouse Chow (Ralston, Purina, St. Louis, MO.) while all other genotypes were given 4 g/day. No differences in body weight were observed due to this dietary treatment between the 65 + / + , + m/ + m, and db + / + m mice After 16 weeks of age, mice were decapitated and livers were immediately excised, weighed, and placed in ice-cold 0.25 M sucrose-O.5 mu disodium ethylenediaminetetraacetate (EDTA) solution at pH 7.4. Mitochondrial respiratory control assay. Mitochondria were obtained from livers and respiratory velocities in resting and active metabolic states were determined (11) by monitoring oxygen consumption at 30” with a biological oxygen monitor (Model 53, Yellow Springs Instrument Co., Yellow Springs, Ohio) and a Clark fixed-voltage polarographic electrode. The 3-ml reaction mixture (pH 7.4) contained 0.33 M mannitol, 10 mM MgCl*, 3.5 mM potassium phosphate, 3.5 mM KCl, 0.33 mM EDTA, 4 mg dialyzed crystalline bovine serum albumin, 1.4 mM L-glutamate or succinate, and mitochondria corresponding to 2.5 mg of mitochondrial protein. Active state respiration commenced on addition of ADP (final concentration was 130 PM). The respiratory control ratio (RCR) is the most sensitive criterion of mitochondrial membrane integrity, and hence phosphorylation capacity, and it is defined as the ratio of ADP stimulated respiratory velocity (active state, state 3) to the velocity obtaining on exhaustion of ADP (resting state, state 4) (12). Mitochondrial protein was estimated in the presence of 1% sodium deoxycholate by a biuret method (13) with crystalline bovine serum albumin as a standard. Statistical analysis. A two-tailed Student t test was used to ascertain levels of significance (14). Probability values of 0.05 or less were considered significant. RESULTS
The intluences of the mouse genotype on body weight, liver weight, mitochondrial content; and respiration are summarized in Table 1. Reducing the food intake of the homozygous diabetic and obese mutant mice to 2 g/day, one-half of the controls’ food intake, resulted in body weights 12 to 13 g higher than their respective controls, the + m/ +m and 65 +/ + mice.
46.6 f 8.6’ 115.0 2 27.7b 2.50 2 0.36
1.5’ 9.7” 0.79
5 + 2 t 0.09’ k o.20b e 0.67
23.7 r 1.4 62.5 t 11.1 2.53 2 0.3
32 1.73 5.49 14.31 13.6 t 40.5 2 3.02 f
9 ” 1 + 0.07 + 0.26 2 0.55
ob/ob
6.2 2 0.8 20.4 k 5.3 3.09 IL 0.42
20 0.89 4.48 8.92
65 +/+
39.6 f 4.5b 127.7 f 22.2’ 3.27 k 0.42
0.9 7.0b 0.59
5 e 2’ ? 0.13’ k 0.19 2 1.47’
12.1 f 45.6 t 3.82 k
35 1.84 5.19 17.71
db+/db+
87.8 2 15.5 2.59 -t0.41
k e + 2
1.2 5.8 1.0 1.66 76.7 2.62 k 15.6 0.66
8.9 23.7 2.89 30.1
o.9b 7.2 0.77 2.8’
9.4 27.7 2.95 34.0
+ 2 + rt
13.37 k
2.9Bb
15.18 k
2.12b
4 22 +- 2 1.07 2 0.07 4.88 -c 0.04
+m/+m
5 26 ” 1” 1.31 + o.14b 4.99 f 0.30
db+/+m
Protein and Respiration
Note. Values are mean -t- standard error of the mean. Glutamate and succinate respiration are expressed as ng atoms of oxygen consumed/min/mg of liver mitochondrial protein. * P < 0.075 compared to the 65. + / + control. ’ P < 0.050 compared to the 65 +/+ control. ’ P < 0.001 compared to the 65 +/+ control.
Number of mice Mouse weight, g Total liver weight, g Liver weight, g/100 g body w Mitochondrial protein, mg/g of liver Glutamate respiration State 4 State 3 Respiratory control ratio Succinate respiration State 4 State 3 Respiratory control ratio
Genotype
TABLE 1 Influence of the Mouse Genotype on Liver Mitochondrial
i s
8 z “b 3
8m *X
g
MITOCHONDRIA
OF DIABETIC
AND
OBESE
MICE
75
Likewise, the db + /db + and ob/ob total liver weights were about twice that of their controls. Thus the db + /db + and ob/ob mice were more efficient in their conversion of food to body weight since one-half the controls’ food intake resulted in a 50% higher body weight, a fourfold difference. Distinct differences were observed in the amount of mitochondrial protein that could be isolated from the livers of the different groups. In particular, the diabetic db+/db+ and the obese ob/ob livers contained twice as much mitochondrial protein per gram of tissue when compared to the 65 + / + controls. Mitochondrial protein levels did not differ in the homozygous misty-coat color mutant + m/ + m and the heterotozygous db + / +m mice. They were intermediate between the high level of the db + /db + and the normal mitochondrial protein level of the 65 +/ +. Both the heterozygous db+/+m and the +m/+m mitochondrial protein levels had large standard errors of the means which reflected a wide range of individual values. Examination of this range revealed individual mitochondrial protein values which were numerically representative of either the 6J +/+ or the db+/db+ mice. A distinct influence of the host genotype on the capacities of isolated mitochondria to oxidize glutamate or succinate was evident. State 3 and 4 respiratory velocities of db + /db + and ob/ob mutant mice were double those of 65 + / + mice. The glutamate and succinate oxidation rates of the db + / + m and the + m/ + m mice were intermediate between the oxidation rates of the db + /db + , ob/ob, and 65 + / + mice. However, the respiratory control ratios were identical for mitochondrial preparations obtained from each of the genotypes. This indicated to us that the phosphorylation efficiency did not vary with the particular mutations, diabetes, db or obese, ob. Only the quantity and total activity of the mitochondria were altered by the mutations diabetes and obese. Thus the ob/ob obese and the db + /db + diabetic mutants’ liver mitochondrial capacity to oxidize glutamate or succinate was three to four times greater than the capacity of the 65 +/+ control. On an organ weight basis, livers from either ob/ob or db + /db + mice were observed to have six to eight times the capacity to oxidize glutamate or succinate when compared with that of 65 +/ + mice. Since there were no significant differences between the homozygous diabetic db + /db + and the obese ob/ob, the observed changes in liver mitochondrial content and oxidative capacity appear to be related to genetic factors associated with obesity, which is common to both mutants. The intermediate capability to oxidize substrate per gram of liver for the heterozygous db + / + m and the homozygous misty + m/ + m may have reflected the bimodal character of individuals that represented either the 65 +/+ or the db+/db+, ob/ob phenotype. DISCUSSION
The homozygous recessive mutations diabetes, db + /db + , and obese, ob/ob, on the inbred C57BL/6J genetic background are associated with hyperphagia, obesity, and the ability to maintain an adequate body weight on restricted food intake. The purpose of this study was to determine whether these mutations had also an effect on liver mitochondria and their function. Based on the comparison between the db+/db+ and ob/ob mutants it is apparent that the changes in liver mitochondrial protein content and the increase in oxidative capacity were
76
ROGERS, HIGGINS, AND LORIA
similar. Consequently, it is suggested that the obese phenotypic be mediated in part by enhanced liver mitochondrial oxidative results in abundant energy that may be utilized for biosynthetic as lipid synthesis. Indeed, liver and adipose tissue lipogenesis doubled in the obese ob/ob mouse (15). These findings provide basis in support of the thrifty gene hypothesis.
expression may capacity which reactions such is more than a biochemical
SUMMARY
Inbred mice with the mutation diabetes C57BL/KsJ db + /db + and the mutation obese C57BL/6J ob/ob displayed a total liver mitochondrial capacity to oxidize glutamate or succinate which was approximately eight times greater than the capacity of the C57BL/6J + / + control mice. This increase in oxidation capacity was estimated by multiplying the observed twofold increase in each of the following components: (a) total liver weight, (b) the mitochondrial protein content per gram of liver, and (c) glutamate or succinate respiration activity per milligram of liver mitochondrial protein. No significant difference in liver mitochondrial function and capacity for oxidation was observed between db + /db + and ob/ob mutants, which indicated that these results may be primarily mediated by the genetic factors responsible for obesity and hyperphagia in these mutants, and not by the genetic traits associated with diabetes. These findings may provide a biochemical foundation in support of the thrifty gene hypothesis. ACKNOWLEDGMENTS The expert technical assistance of Wilson Friend and Louise B. Montgomery is appreciated. This work was supported in part by NIH Arthritis, Metabolic, Digestive and Kidney Diseases Institute Grants AM21872 and AM24097.
REFERENCES 1. Parks, R. E., Jr., Adler, J., and Copenhaven, J. H., J. Biol. Chem. 214, 693 (1955). 2. Hall, J. C., Sordahl, L. A., and Stetko, P. L., J. Biol. Chem. 235, 1536 (1960). 3. Mackerer, C. R., Paquet, R. J., Mehlman, M., and Tobin, R. B., Proc. Sot. Exp. Biol. Med. 137, 992 (1971). 4. DiMarco, J. P., and Hoppel, L., J. Clin. Invtst, 55, 1237 (1975). 5. Neel, J. V., Amer. J. Hum. Genet. 14, 353, (1962). 6. Hunt, C. E., Lindsey, J. R., and Welkby, S. U., Fed. Proc. 35, 1206 (1976). 7. Wyse, B. M., and Dubbin, W. E., Diabetologia 6, 267 (1970). 8. Webb, S. A., Loria, R. M., and Madge, G. E., Curr. Microbial. 3, 15 (1979). 9. Coleman, D. L., Metabolism 32, 162 (1983). 10. Herberg, L., and Coleman, D. L., Metabolism 26, 59 (1977). 11. Rogers, K. S., and Higgins, E. S., J. Biol. Chem. 248, 7142 (1973). 12. Chance, B., and Williams, G. R., Adv. Enzymol. 17, 65 (1956). 13. Gomall, A. G., Bardawill, C. J., and David, M., J. Biol. Chem. 177, 751 (1949). 14. Edwards, A. L., “Statistical Analyses,” p. 127. Rinehart, New York, 1958. 15. Coleman, D. L., and Brodoff, B. N., in “Diabetes Mellitus and Obesity” (B. N. Brodoff, and S. J. Bleicher, Eds.), p. 283, Williams & Wilkins, Baltimore, Md., 1982.
MEDICINE
Influence
KENNETH
AND
METABOLIC
BIOLOGY
35, 72-76 (1986)
of Genetic Predisposition to Diabetes and Obesity on Mitochondrial Function S. ROGERS,EDWIN S. HIGGINS, AND ROGERM. LORIA
Departments of Biochemistry, Microbiology and Immunology, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298 Received December 11, 1984
The importance of the mitochondrion in diabetes mellitus has been somewhat clouded by the diverse results obtained when diabetes was experimentally produced by drugs. For example, Parks et al. (1) reported that hepatic mitochondria were not affected in their uptake of inorganic phosphate or oxygen when organelles were obtained from rats treated with alloxan. On the other hand, Hall et al. (2) reported that rats treated with alloxan had hepatic mitochondria that were deficient in their ability to synthesize ATP. Mackerer e? al. (3) showed that alloxan and streptozotocin potentiated the efficiency with which rat liver mitochondria phosphorylated ADP by stimulating respiratory control without affecting P: 0 ratios. DiMarco and Hoppel (4) said that streptozotocin did not affect either mitochondrial protein content per gram of rat liver or mitochondrial respiratory control in their experiments. Neel (5) linked both the dietary and hereditary components of ,obesity and diabetes mellitus under the “thrifty genotype” hypothesis which states that certain gene(s) or mutation(s) may be favorable when food supply is limited but unfavorable when food is in abundance. The homozygous mutant mice C57BL/KsJ db + /db + and C57BL/6J ob/ob are hyperphagic, obese, and diabetic (6). These animals can maintain a normal body weight or increase their body fat even when their dietary intake is restricted from one-half to two-thirds of the amount of food intake by normal mice; i.e., 4 g/day may be lowered to 2 g/day (7- 9). We have used the inbred diabetic mutant mice, db+ /db+ , and the obese mutant mice, ob/ob, rather than chemically induced diabetes, as a model to study the influences of hyperphagia, obesity, and diabetes on respiratory control of liver mitochondria. Our results show that the spontaneous homozygous mutations, diabetes db+ /db+ , and obese, ob/ob, exert a significant influence on liver mitochondrial respiratory properties. MATERIALS AND METHODS
Inbred C57BL/6J mice with the homozygous diabetic mutation, db +/db +, the doubly heterozygous mutation, db + /+ m, or the homozygous mutation, 72 0885-4505/86 $3.00 Copyright All rights
0 1986 by Academic Press, Inc. of reproduction in any form reserved.
MITOCHONDRIA
OF DIABETIC
AND OBESE MICE
13
+ m/ + m, on this inbred genetic background were used as one group. On this genetic background the db+/db+ mutation results in hyperphagia, obesity, hyperglycemia, and spontaneous diabetes. The doubly heterozygote db + / + m is not hyperphagic, is not obese, and does not develop spontaneous diabetes. The homozygote, misty coat color mutant, + m/ + m, is lean and does not develop diabetes. The second group of experimental animals included the homozygous obese C57BL/6J ob/ob mutant and its inbred C57BL/6J +/ + control. The homozygous ob/ob is also hyperphagic, is obese, and develops a spontaneous diabetes-like disease. However, in the obese mutant, hyperinsulinemia is markedly higher than in the diabetic mutant db, and uncontrolled hyperglycemia and destruction of islet cells, which occurs in the diabetic db mutant, are not observed (10). Male mice 6 weeks old were purchased from the Jackson Laboratories (Bar Harbor, Maine). Mice were individually caged and placed on a light regime of 12 hr on/12 hr off. Water was provided ad libitum to all animals. To limit the effects of hyperphagia and obesity, db+/db+ and ob/ob mice were fed 2 g/day Purina Laboratory Mouse Chow (Ralston, Purina, St. Louis, MO.) while all other genotypes were given 4 g/day. No differences in body weight were observed due to this dietary treatment between the 65 + / + , + m/ + m, and db + / + m mice After 16 weeks of age, mice were decapitated and livers were immediately excised, weighed, and placed in ice-cold 0.25 M sucrose-O.5 mu disodium ethylenediaminetetraacetate (EDTA) solution at pH 7.4. Mitochondrial respiratory control assay. Mitochondria were obtained from livers and respiratory velocities in resting and active metabolic states were determined (11) by monitoring oxygen consumption at 30” with a biological oxygen monitor (Model 53, Yellow Springs Instrument Co., Yellow Springs, Ohio) and a Clark fixed-voltage polarographic electrode. The 3-ml reaction mixture (pH 7.4) contained 0.33 M mannitol, 10 mM MgCl*, 3.5 mM potassium phosphate, 3.5 mM KCl, 0.33 mM EDTA, 4 mg dialyzed crystalline bovine serum albumin, 1.4 mM L-glutamate or succinate, and mitochondria corresponding to 2.5 mg of mitochondrial protein. Active state respiration commenced on addition of ADP (final concentration was 130 PM). The respiratory control ratio (RCR) is the most sensitive criterion of mitochondrial membrane integrity, and hence phosphorylation capacity, and it is defined as the ratio of ADP stimulated respiratory velocity (active state, state 3) to the velocity obtaining on exhaustion of ADP (resting state, state 4) (12). Mitochondrial protein was estimated in the presence of 1% sodium deoxycholate by a biuret method (13) with crystalline bovine serum albumin as a standard. Statistical analysis. A two-tailed Student t test was used to ascertain levels of significance (14). Probability values of 0.05 or less were considered significant. RESULTS
The intluences of the mouse genotype on body weight, liver weight, mitochondrial content; and respiration are summarized in Table 1. Reducing the food intake of the homozygous diabetic and obese mutant mice to 2 g/day, one-half of the controls’ food intake, resulted in body weights 12 to 13 g higher than their respective controls, the + m/ +m and 65 +/ + mice.
46.6 f 8.6’ 115.0 2 27.7b 2.50 2 0.36
1.5’ 9.7” 0.79
5 + 2 t 0.09’ k o.20b e 0.67
23.7 r 1.4 62.5 t 11.1 2.53 2 0.3
32 1.73 5.49 14.31 13.6 t 40.5 2 3.02 f
9 ” 1 + 0.07 + 0.26 2 0.55
ob/ob
6.2 2 0.8 20.4 k 5.3 3.09 IL 0.42
20 0.89 4.48 8.92
65 +/+
39.6 f 4.5b 127.7 f 22.2’ 3.27 k 0.42
0.9 7.0b 0.59
5 e 2’ ? 0.13’ k 0.19 2 1.47’
12.1 f 45.6 t 3.82 k
35 1.84 5.19 17.71
db+/db+
87.8 2 15.5 2.59 -t0.41
k e + 2
1.2 5.8 1.0 1.66 76.7 2.62 k 15.6 0.66
8.9 23.7 2.89 30.1
o.9b 7.2 0.77 2.8’
9.4 27.7 2.95 34.0
+ 2 + rt
13.37 k
2.9Bb
15.18 k
2.12b
4 22 +- 2 1.07 2 0.07 4.88 -c 0.04
+m/+m
5 26 ” 1” 1.31 + o.14b 4.99 f 0.30
db+/+m
Protein and Respiration
Note. Values are mean -t- standard error of the mean. Glutamate and succinate respiration are expressed as ng atoms of oxygen consumed/min/mg of liver mitochondrial protein. * P < 0.075 compared to the 65. + / + control. ’ P < 0.050 compared to the 65 +/+ control. ’ P < 0.001 compared to the 65 +/+ control.
Number of mice Mouse weight, g Total liver weight, g Liver weight, g/100 g body w Mitochondrial protein, mg/g of liver Glutamate respiration State 4 State 3 Respiratory control ratio Succinate respiration State 4 State 3 Respiratory control ratio
Genotype
TABLE 1 Influence of the Mouse Genotype on Liver Mitochondrial
i s
8 z “b 3
8m *X
g
MITOCHONDRIA
OF DIABETIC
AND
OBESE
MICE
75
Likewise, the db + /db + and ob/ob total liver weights were about twice that of their controls. Thus the db + /db + and ob/ob mice were more efficient in their conversion of food to body weight since one-half the controls’ food intake resulted in a 50% higher body weight, a fourfold difference. Distinct differences were observed in the amount of mitochondrial protein that could be isolated from the livers of the different groups. In particular, the diabetic db+/db+ and the obese ob/ob livers contained twice as much mitochondrial protein per gram of tissue when compared to the 65 + / + controls. Mitochondrial protein levels did not differ in the homozygous misty-coat color mutant + m/ + m and the heterotozygous db + / +m mice. They were intermediate between the high level of the db + /db + and the normal mitochondrial protein level of the 65 +/ +. Both the heterozygous db+/+m and the +m/+m mitochondrial protein levels had large standard errors of the means which reflected a wide range of individual values. Examination of this range revealed individual mitochondrial protein values which were numerically representative of either the 6J +/+ or the db+/db+ mice. A distinct influence of the host genotype on the capacities of isolated mitochondria to oxidize glutamate or succinate was evident. State 3 and 4 respiratory velocities of db + /db + and ob/ob mutant mice were double those of 65 + / + mice. The glutamate and succinate oxidation rates of the db + / + m and the + m/ + m mice were intermediate between the oxidation rates of the db + /db + , ob/ob, and 65 + / + mice. However, the respiratory control ratios were identical for mitochondrial preparations obtained from each of the genotypes. This indicated to us that the phosphorylation efficiency did not vary with the particular mutations, diabetes, db or obese, ob. Only the quantity and total activity of the mitochondria were altered by the mutations diabetes and obese. Thus the ob/ob obese and the db + /db + diabetic mutants’ liver mitochondrial capacity to oxidize glutamate or succinate was three to four times greater than the capacity of the 65 +/+ control. On an organ weight basis, livers from either ob/ob or db + /db + mice were observed to have six to eight times the capacity to oxidize glutamate or succinate when compared with that of 65 +/ + mice. Since there were no significant differences between the homozygous diabetic db + /db + and the obese ob/ob, the observed changes in liver mitochondrial content and oxidative capacity appear to be related to genetic factors associated with obesity, which is common to both mutants. The intermediate capability to oxidize substrate per gram of liver for the heterozygous db + / + m and the homozygous misty + m/ + m may have reflected the bimodal character of individuals that represented either the 65 +/+ or the db+/db+, ob/ob phenotype. DISCUSSION
The homozygous recessive mutations diabetes, db + /db + , and obese, ob/ob, on the inbred C57BL/6J genetic background are associated with hyperphagia, obesity, and the ability to maintain an adequate body weight on restricted food intake. The purpose of this study was to determine whether these mutations had also an effect on liver mitochondria and their function. Based on the comparison between the db+/db+ and ob/ob mutants it is apparent that the changes in liver mitochondrial protein content and the increase in oxidative capacity were
76
ROGERS, HIGGINS, AND LORIA
similar. Consequently, it is suggested that the obese phenotypic be mediated in part by enhanced liver mitochondrial oxidative results in abundant energy that may be utilized for biosynthetic as lipid synthesis. Indeed, liver and adipose tissue lipogenesis doubled in the obese ob/ob mouse (15). These findings provide basis in support of the thrifty gene hypothesis.
expression may capacity which reactions such is more than a biochemical
SUMMARY
Inbred mice with the mutation diabetes C57BL/KsJ db + /db + and the mutation obese C57BL/6J ob/ob displayed a total liver mitochondrial capacity to oxidize glutamate or succinate which was approximately eight times greater than the capacity of the C57BL/6J + / + control mice. This increase in oxidation capacity was estimated by multiplying the observed twofold increase in each of the following components: (a) total liver weight, (b) the mitochondrial protein content per gram of liver, and (c) glutamate or succinate respiration activity per milligram of liver mitochondrial protein. No significant difference in liver mitochondrial function and capacity for oxidation was observed between db + /db + and ob/ob mutants, which indicated that these results may be primarily mediated by the genetic factors responsible for obesity and hyperphagia in these mutants, and not by the genetic traits associated with diabetes. These findings may provide a biochemical foundation in support of the thrifty gene hypothesis. ACKNOWLEDGMENTS The expert technical assistance of Wilson Friend and Louise B. Montgomery is appreciated. This work was supported in part by NIH Arthritis, Metabolic, Digestive and Kidney Diseases Institute Grants AM21872 and AM24097.
REFERENCES 1. Parks, R. E., Jr., Adler, J., and Copenhaven, J. H., J. Biol. Chem. 214, 693 (1955). 2. Hall, J. C., Sordahl, L. A., and Stetko, P. L., J. Biol. Chem. 235, 1536 (1960). 3. Mackerer, C. R., Paquet, R. J., Mehlman, M., and Tobin, R. B., Proc. Sot. Exp. Biol. Med. 137, 992 (1971). 4. DiMarco, J. P., and Hoppel, L., J. Clin. Invtst, 55, 1237 (1975). 5. Neel, J. V., Amer. J. Hum. Genet. 14, 353, (1962). 6. Hunt, C. E., Lindsey, J. R., and Welkby, S. U., Fed. Proc. 35, 1206 (1976). 7. Wyse, B. M., and Dubbin, W. E., Diabetologia 6, 267 (1970). 8. Webb, S. A., Loria, R. M., and Madge, G. E., Curr. Microbial. 3, 15 (1979). 9. Coleman, D. L., Metabolism 32, 162 (1983). 10. Herberg, L., and Coleman, D. L., Metabolism 26, 59 (1977). 11. Rogers, K. S., and Higgins, E. S., J. Biol. Chem. 248, 7142 (1973). 12. Chance, B., and Williams, G. R., Adv. Enzymol. 17, 65 (1956). 13. Gomall, A. G., Bardawill, C. J., and David, M., J. Biol. Chem. 177, 751 (1949). 14. Edwards, A. L., “Statistical Analyses,” p. 127. Rinehart, New York, 1958. 15. Coleman, D. L., and Brodoff, B. N., in “Diabetes Mellitus and Obesity” (B. N. Brodoff, and S. J. Bleicher, Eds.), p. 283, Williams & Wilkins, Baltimore, Md., 1982.