Tumor necrosis factor-alpha stimulates cell proliferation in adipose tissue-derived stromal-vascular cell culture: promotion of adipose tissue expansion by paracrine growth factors.

OBJECTIVE: Elevated levels of tumor necrosis factor-alpha (TNF-alpha) protein and mRNA have been reported in adipose tissue from obese humans and rodents. However, TNF-alpha has catabolic and antiadipogenic effects on adipocytes. Addressing this paradox, we tested the hypothesis that paracrine levels of TNF-alpha, alone or together with insulin-like growth factor-I (IGF-I), support preadipocyte development. RESEARCH METHODS AND PROCEDURES: Cultured stromal-vascular cells from rat inguinal fat depots were exposed to serum-free media containing insulin and 0.2 nM TNF-alpha, 2.0 nM TNF-alpha, or 0.2 nM TNF-alpha + 1.0 nM IGF-I at different times during 7 days of culture. RESULTS: TNF-alpha inhibited adipocyte differentiation as indicated by a reduction in both immunocytochemical reactivity for the preadipocyte-specific antigen (AD3; early differentiation marker) and glycerol-3-phosphate dehydrogenase activity (late differentiation marker). Early exposure (Days 1 through 3 of culture) to 0.2 nM TNF-alpha did not have a long term effect on inhibiting differentiation. Continuous exposure to 0.2 nM TNF-alpha from Days 1 through 7 of culture resulted in a 75% increase in cell number from control. There was a synergistic effect of 0.2 nM TNF-alpha + 1 nM IGF-I on increasing cell number by Day 7 of culture to levels greater than those observed with either treatment applied alone. DISCUSSION: These data suggest that paracrine levels (0.2 nM) of TNF-alpha alone or in combination with IGF-I may support adipose tissue development by increasing the total number of stromal-vascular and/or uncommitted cells within the tissue. These cells may then be recruited to become preadipocytes or may alternatively serve as infrastructure to support adipose tissue growth.

Insulin-like growth factor I mediates high-fat diet-induced adipogenesis in Osborne-Mendel rats.

To determine if high-fat (HF) diet-induced changes in adipose tissue cellularity are associated with the presence of paracrine growth factor(s) that alter preadipocyte proliferation, Osborne-Mendel rats were fed either a HF (76% energy) or a low-fat (LF, 12% energy) diet for 85 days. HF-fed rats had greater (P < 0.05) fat pad size, total fat cell number, number of small (30-70 microm) and large (80-140 microm) adipocytes, and percentage of 100- to 140-microm adipocytes compared with LF-fed rats. Preadipocytes in primary cell culture treated with inguinal adipose tissue conditioned medium (ATCM) prepared from HF-fed rats had greater (P < 0.05) proliferation compared with cultures treated with ATCM from LF-fed rats. Proliferative capacity of ATCM prepared from HF-fed rats was attenuated after the stripping of the medium of insulin-like growth factor I using an immunomagnetic bead separation system. These data are consistent with the concept that insulin-like growth factor I is involved in the paracrine regulation of adipogenesis.

Adipocyte development is dependent upon stem cell recruitment and proliferation of preadipocytes.

OBJECTIVES: The ability to acquire fat cells persists over the life spans of animals. It is unknown whether adipocyte acquisition is the result of preadipocyte proliferation or stem cell recruitment to become adipocytes. The purposes of these studies were 1) to characterize early differentiation of stromal vascular (S-V) cells to preadipocytes as it is influenced by insulin, dexamethasone (DEX), and insulin-like growth factor-I (IGF-I); and 2) to determine whether new fat cells arise from stem cell recruitment or preadipocyte proliferation. RESEARCH METHODS AND PROCEDURES: Freshly isolated S-V cells from rat inguinal adipose tissues were plated for 24 hours then exposed to serum-free medium. RESULTS: Approximately 15% of freshly plated S-V cells were preadipocytes as determined by a preadipocyte specific marker, AD3. Total cell number and proportion of preadipocytes were significantly greater with 100 nM insulin treatment than with 0, 0.1, or 1.0 nM, but IGF-I treatment at 10 nM resulted in preadipocyte development similar to that with 100 nM insulin treatment. The addition of 5 nM DEX to the 100 nM insulin treatment resulted in a 20% increase in preadipocyte number by day 2 when compared to either treatment alone. 5-Bromo-2'-deoxy-uridine treatment suppressed the increased proportion of preadipocytes from days 0-2 in non-insulin treated cells and prevented the increase typically observed with insulin. A mitosis inhibitor also significantly reduced the proportion of preadipocytes. DISCUSSION: These results show for the first time that S-V cells are recruited as preadipocytes and that proliferation of these preadipocytes and early differentiation occur simultaneously.

Whole-egg diet delays the age-related impaired glucose tolerance of BHE/Cdb rats.

The effects of dietary egg on the age-related progression of impaired glucose tolerance and glomerulonephropathy in diabetes-prone BHE/Cdb rats were studied. This rat strain mimics the human with NIDDM. The development of impaired glucose tolerance was delayed in rats fed the whole-egg diet, however, feeding this diet resulted in elevated hepatic weight but had no effect on the age-related changes in renal lesions or renal function. We conclude that in this animal model for NIDDM, the development of glomerulonephropathy is independent of the development of impaired glucose tolerance and that diet can affect the time course for impaired glucose tolerance without affecting renal disease development.

Menhaden oil feeding increases potential for renal free radical production in BHE/cdb rats.

The effects of feeding 9% beef tallow (BT) or menhaden oil (MO) in a 10% fat-60% sucrose-20% protein diet on renal cortex fatty acid profile, renal lipid peroxide formation potential, and the blood pressure response to a norepinephrine challenge was studied. Male weanling BHE/cdb prediabetic rats were studied after 8 weeks of diet treatment. Half the rats were subjected to a norepinephrine challenge, and their mean arterial blood pressure was determined. Plasma renin and angiotensin II levels were determined in the presence or absence of the challenge. The source of dietary fat had no effect on these measurements. MO fed rats had a greater potential to form lipid free radicals in the kidney than BT fed rats despite the fact that the renal tissue from both groups had an equivalent number of unsaturations on a mole % basis. From these results we conclude that the accelerated renal disease in menhaden oil fed rats is not due to a diet fat effect on blood pressure regulation but might be due to a diet fat effect on free radical production. These free radicals can be cytotoxic and if produced in large amounts could result in a loss of glomerular cells. Whether this occurs and can be reversed by a change in diet was not determined.

Voluntary running in male S5B/P1Ras rats fed high fat or high carbohydrate diets.

Nineteen week-old male S5B/P1Ras (S5B) rats were randomly assigned to one of 4 groups as follows: (a) activity wheel access (running)/high fat diet (RF); (b) no activity wheel access (non-running)/high fat diet (NRF); (c) activity wheel access (running)/high carbohydrate diet (RC); and (d) no activity wheel access (non-running)/high carbohydrate diet (NRC) for the seven weeks duration of the experiment. Throughout the 7 wk of the experiment, rats ran more during subsequent weeks than they did the previous week. RC rats ran more than RF rats as measured by the running slopes. All groups of rats lost weight at the initiation of the experiment but significantly more weight was lost by running rats than their nonrunning counterparts. The inguinal, epididymal and perirenal/retroperitoneal (P/R) fat depots weighed significantly less in the running than in the nonrunning groups. From among the 3 fat depots, the difference was greatest in the P/R depot. There were no diet or voluntary activity effects on plasma corticosterone concentrations except at week 2 when running rats had higher concentrations than nonrunning rats.