Enzyme histochemical differentiation of white adipose tissue in the rat

Adipose Tissue Development Relies on Coordinated Extracellular Matrix Remodeling, Angiogenesis, and Adipogenesis

Despite developing prenatally, the adipose tissue is unique in its ability to undergo drastic growth even after reaching its mature size. This development and subsequent maintenance rely on the proper coordination between the vascular niche and the adipose compartment. In this review, the process of adipose tissue development is broken down to explain (1) the ultrastructural matrix remodeling that is undertaken during simultaneous adipogenesis and angiogenesis, (2) the paracrine crosstalk involved during adipose development, (3) the mechanical regulators involved in adipose growth, and (4) the proteolytic and paracrine oversight for matrix remodeling during adipose development. It is crucial to gain a better understanding of the complex relationships that exist between adipose tissue and the vasculature during tissue development to provide insights into the pathological tissue expansion of obesity and to develop improved soft-tissue reconstruction techniques.

In utero programming of later adiposity: the role of fetal growth restriction

Intrauterine growth restriction (IUGR) is strongly associated with obesity in adult life. The mechanisms contributing to the onset of IUGR-associated adult obesity have been studied in animal models and humans, where changes in fetal adipose tissue development, hormone levels and epigenome have been identified as principal areas of alteration leading to later life obesity. Following an adverse in utero development, IUGR fetuses display increased lipogenic and adipogenic capacity in adipocytes, hypoleptinemia, altered glucocorticoid signalling, and chromatin remodelling, which subsequently all contribute to an increased later life obesity risk. Data suggest that many of these changes result from an enhanced activity of the adipose master transcription factor regulator, peroxisome proliferator-activated receptor-γ (PPARγ) and its coregulators, increased lipogenic fatty acid synthase (FAS) expression and activity, and upregulation of glycolysis in fetal adipose tissue. Increased expression of fetal hypothalamic neuropeptide Y (NPY), altered hypothalamic leptin receptor expression and partitioning, reduced adipose noradrenergic sympathetic innervations, enhanced adipose glucocorticoid action, and modifications in methylation status in the promoter of hepatic and adipose adipogenic and lipogenic genes in the fetus also contribute to obesity following IUGR. Therefore, interventions that inhibit these fetal developmental changes will be beneficial for modulation of adult body fat accumulation.

Structural and histochemical aspects of perirenal adipose tissue in fetal pigs: relationships between stromal-vascular characteristics and fat cell concentration and enzyme activity

Samples of perirenal adipose tissue were obtained from four fetuses from each of seven crossbred gilts at each of three stages of gestation: 70, 90, and 110 days. Samples were routinely prepared for histochemistry and histology. At each age, the largest fat cell clusters were consistently located near points where large blood vessels entered the loose connective tissue. Cell-cluster size decreased with distance from the entry points of large blood vessels. Fat cells proximal to entry points of large arterioles and fat cells distal to entry points of large arterioles were the same size. Enzyme cytochemistry disclosed that reactions for glucose-6-phosphate dehydrogenase (G6PDH), lipoprotein lipase (LPL) and NADH-TR enzymes were reduced in distal (relative to entry points of large arterioles) adipocytes compared with proximal adipocytes. Reactions for succinate dehydrogenase (SDH) and lactate dehydrogenase (LDH) in adipocytes were not influenced by location within the tissue. Small fat cell clusters with sparse capillary beds surround arterioles in distal areas of sections from fetuses at 70, 90, and 110 days of gestation. In the proximal areas of sections from 110-day-old fetuses, arterioles were surrounded by large fat cell clusters with dense capillary beds. These characteristics serve to distinguish perirenal depots from subcutaneous depots in the fetus.

Characterization of rabbit stromal fibroblasts derived from red and yellow bone marrow

Rabbit stromal fibroblasts subcultured from red and yellow bone marrow and implanted beneath the renal capsule form ossicles the hemic cellularity of which mirrors the cellularity of the marrow used for culture. Although the cultured red and yellow marrow cells are similar in fine-structural appearance, they differ strikingly in enzymatic content of alpha-naphthylbutyrate esterase, which is abundant only in the cells derived from yellow marrow. Other observers (20, 21) have proposed that stromal fibroblasts are preadipocytes, and this data suggests that those derived from yellow marrow have the phenotype of more differentiated adipocytes. On the other hand, fibroblasts derived from red and yellow bone marrow show no differences in their profiles of procollagen synthesis. Both types of fibroblasts secrete type III procollagen as the major species, with a I/III ratio of 1:3; in contrast, rabbit dermal fibroblasts have a prominent peak of type I procollagen. The similarity of stromal cells derived from red and yellow bone marrow in procollagen synthesis suggests that the collagen part of the extracellular matrix is not the only basis for their intrinsic difference in capacity for hematopoiesis.

Lipoblastomatosis: ultrastructure of two cases and relationship to human fetal white adipose tissue

Two cases of lipoblastomatosis were examined by electron microscopy. In each there was a spectrum of adipose cell differentiation from mature adipocytes to undifferentiated mesenchymal cells. The cells had various shapes and were loosely related to one another and to small blood vessels in a stroma containing sparse collagen and proteoglycan granules. Adipocytes and lipoblasts had a discrete basal lamina but this was absent in immature mesenchymal cells, which had prominent intermediate (10-nm) microfilaments and few or no lipid droplets. Neither case had foci resembling brown adipose tissue or hibernoma (large polygonal cells closely apposed to one another and to capillaries with densely packed pleomorphic mitochondria and focal undulating plasmalemmal invaginations). Both the ultrastructure of lipoblastomatosis and its characteristic loose lobular arrangement by light microscopy closely resemble human fetal "white" adipose tissue.

Nucleoside phosphatase and nucleotide tetrazolium reductase as markers of arteriolar differentiation in fetal pig tissue

Nucleoside phosphatase and nucleotide tetrazolium reductase reactions were studied as potential markers of arteriolar differentiation. Arteriolar systems were analyzed cytochemically and morphologically in a variety of fetal pig tissues at 70 and 110 days of gestation. In skeletal muscle and subcutaneous adipose tissue there were age dependent changes in phosphatase and reductase reactivity in arteriolar vessels. These changes were temporally associated with the morphological differentiation of the tunica medial arteriolar layer. There were no age dependent changes in the cytochemistry of arterioles in liver and cardiac muscle. In the youngest fetuses, arterioles in liver and cardiac muscle displayed a typical tunica medial layer (normal morphology). The cytochemical reactions (phosphatase, reductase) of arterioles in cardiac muscle and liver from 70 (and 110) days old fetuses were identical to cytochemical reactions of arterioles in muscle and adipose tissue from 110 days old fetuses. In the skin, there were age dependent increases in phosphatase reactive arterioles and capillaries. Capillary staining (phosphatase) and capillary bed size were inversely correlated in the skin. Capillaries in skeletal muscle, cardiac muscle, adipose tissue and liver were not phosphatase reactive. These results indicate that the morphological and cytochemical differentiation of arterioles is dependent on tissue and age in the fetal pig. Furthermore, several histochemical techniques (phosphatase, reductases) are validated as simple means to analyze arteriolar differentiation in general.