Cellular origins of cold-induced brown adipocytes in adult mice.

This work investigated how cold stress induces the appearance of brown adipocytes (BAs) in brown and white adipose tissues (WATs) of adult mice. In interscapular brown adipose tissue (iBAT), cold exposure increased proliferation of endothelial cells and interstitial cells expressing platelet-derived growth factor receptor, α polypeptide (PDGFRα) by 3- to 4-fold. Surprisingly, brown adipogenesis and angiogenesis were largely restricted to the dorsal edge of iBAT. Although cold stress did not increase proliferation in inguinal white adipose tissue (ingWAT), the percentage of BAs, defined as multilocular adipocytes that express uncoupling protein 1, rose from undetectable to 30% of total adipocytes. To trace the origins of cold-induced BAs, we genetically tagged PDGFRα(+) cells and adipocytes prior to cold exposure, using Pdgfra-Cre recombinase estrogen receptor T2 fusion protein (CreER(T2)) and adiponectin-CreER(T2), respectively. In iBAT, cold stress triggered the proliferation and differentiation of PDGFRα(+) cells into BAs. In contrast, all newly observed BAs in ingWAT (5207 out of 5207) were derived from unilocular adipocytes tagged by adiponectin-CreER(T2)-mediated recombination. Surgical denervation of iBAT reduced cold-induced brown adipogenesis by >85%, whereas infusion of norepinephrine (NE) mimicked the effects of cold in warm-adapted mice. NE-induced de novo brown adipogenesis in iBAT was eliminated in mice lacking ß1-adrenergic receptors. These observations identify a novel tissue niche for brown adipogenesis in iBAT and further define depot-specific mechanisms of BA recruitment.

Identification of an adipogenic niche for adipose tissue remodeling and restoration.

The regulatory events guiding progenitor activation and differentiation in adult white adipose tissue are largely unknown. We report that induction of brown adipogenesis by ß3-adrenergic receptor (ADRB3) activation involves the death of white adipocytes and their removal by M2-polarized macrophages. Recruited macrophages express high levels of osteopontin (OPN), which attracts a subpopulation of PDGFRα+ progenitors expressing CD44, a receptor for OPN. Preadipocyte proliferation is highly targeted to sites of adipocyte clearance and occurs almost exclusively in the PDGFRα+ CD44+ subpopulation. Knockout of OPN prevents formation of crown-like structures by ADRB3 activation and the recruitment, proliferation, and differentiation of preadipocytes. The recruitment and differentiation of PDGFRα+ progenitors are also observed following physical injury, during matrix-induced neogenesis, and in response to high-fat feeding. Each of these conditions recruits macrophages having a unique polarization signature, which may explain the timing of progenitor activation and the fate of these cells in vivo.

In vivo identification of bipotential adipocyte progenitors recruited by ß3-adrenoceptor activation and high-fat feeding.

Nutritional and pharmacological stimuli can dramatically alter the cellular phenotypes in white adipose tissue (WAT). Utilizing genetic lineage tracing techniques, we demonstrate that brown adipocytes (BA) that are induced by ß3-adrenergic receptor activation in abdominal WAT arise from the proliferation and differentiation of cells expressing platelet-derived growth factor receptor alpha (PDGFRα), CD34, and Sca-1 (PDGFRα(+) cells). PDGFRα(+) cells have a unique morphology in which extended processes contact multiple cells in the tissue microenvironment. Surprisingly, these cells also give rise to white adipocytes (WA) that can comprise up to 25% of total fat cells in abdominal fat pads following 8 weeks of high-fat feeding. Isolated PDGFRα(+) cells differentiated into both BA and WA in vitro and generated WA after transplantation in vivo. The identification of PDGFRα(+) cells as bipotential adipocyte progenitors will enable further investigation of mechanisms that promote therapeutic cellular remodeling in adult WAT.

The effect of dystocia and previous cesarean uterine scar on the tensile properties of the lower uterine segment.

OBJECTIVE: The remodeling of uterine connective tissue during labor can lead to the reorganization of the extracellular matrix that, in turn, may influence the biomechanical properties of the myometrial wall. We hypothesized that the stretching of the lower uterine segment in laboring women with dystocia changes the viscoelastic properties of the uterine wall. STUDY DESIGN: We tested the tensile strength of lower uterine segment myometrium in 68 pregnant women at term. The biomechanical, structural, and biochemical properties were compared among 3 groups: (1) 39 laboring women who underwent primary low-transverse cesarean delivery for labor dystocia, (2) 12 nonlaboring women who underwent primary elective low-transverse cesarean delivery and (3) 17 women who underwent an elective repeat low-transverse cesarean delivery at term. The tensile properties were quantitated with a stretching regimen that was designed to mimic the conditions of labor. Parameters such as slope, yield point, and break point were recorded, analyzed, and interpreted. Biochemical properties were determined by the measurement of the sulfated glycosaminoglycans, hydroxyproline, and pyridinoline-deoxypyridinoline. Histologic properties of the connective tissue were assessed by collagen birefringence. Lastly, the association between these properties and biomechanical responses were compared among groups. RESULTS: Lower uterine segment myometrium specimens obtained from laboring women were stiffer compared with specimens from women who were not in labor (P = .013) or had scarred myometrium (P < .001). The force that was required to reach the yield point was similar between labor and nonlabor groups (P = .216). Likewise, a previous lower uterine segment scar did not alter the yield point. The break point was similar among all groups (P = .317). Sulfated glycosaminoglycan levels were unaffected by labor or scarring (P = .354). Scarred lower uterine segment myometrium had a higher collagen content compared with unscarred myometrium specimens that were obtained during labor (P = .025). Although there were similar degrees of collagen cross-linking among groups (P = .212), there was lower collagen birefringence in myometrium from laboring women compared with nonlaboring women (P < .001). CONCLUSION: Labor alters the viscoelastic properties of myometrium. Lower uterine segment myometrium is stiffest in women with dysfunctional labor compared with nonlabor control subjects. Labor and scarring also alter the pattern of collagen birefringence. Similar collagen cross-linking among the study groups may explain the reason that the breaking strength of the tissue is not altered by the state of labor and the reason that the rupture of the uterine scar is a rare event.

The novel antimicrobial peptide beta3-defensin is produced by the amnion: a possible role of the fetal membranes in innate immunity of the amniotic cavity.

BACKGROUND: Innate immunity evolved to eliminate microorganisms before, or after their entry into the tissues, but before enough antigen is available to activate an adaptive, immune response. Innate immunity is so successful that the majority of encountered microbes are neutralized. The beta-defensins are antimicrobial peptides produced by skin and mucosal surfaces and are an integral part of the innate immune system. The ability of the amnion cells, which are epithelial derivatives, to produce antimicrobial beta-defensins has not been explored. OBJECTIVE: This study was undertaken to test the hypothesis that amnion cells synthesize beta-defensins under either basal or stimulated conditions. METHODS: Amnion epithelial FL cells (ATCC CCL 62) were cultured in Ham's F12 and Dulbecco's modified Eagle medium plus 10% fetal calf serum until confluence, then replated into 24-well plates at 1.5 million cells per well. Cells from triplicate wells were harvested after 1, 3, 6, and 24 hours of exposure to microbial wall components (lipopolysaccharide [LPS]: 1 microg/mL or peptidoglycan [PG]: 10 microg/mL). Reverse transcription real-time polymerase chain reaction was performed with the use of human-specific primers for beta1, beta2, beta3, and beta4 defensins to compare basal messenger RNA (mRNA) levels of defensins and in response to treatment. beta-actin was used for standardization. Protein expression was investigated by immunofluorescence of the cells in culture, and by immunohistochemistry in paraffin sections of human fetal membranes from pregnancies with or without histologic chorioamnionitis. RESULTS: Amnion FL cells expressed mRNA for all known beta-defensins with beta3-defensin mRNA levels significantly higher compared with others ( P < .001, 1-way analysis of variance [ANOVA]). beta3 was the only beta-defensin whose mRNA was upregulated in response to the microbial mimics LPS (1-way ANOVA, P = .019) and PG (1-way ANOVA, P = .011). Immunofluorescence confirmed that beta3-defensin protein was present in cultured amnion cells, and upregulated in response to PG and LPS in distinct cells. Similarly, in tissue sections of human fetal membranes amnion epithelium was intensely positive for beta3-defensin protein by immunohistochemistry. Conspicuous beta3-defensin staining was also detected in the chorio-decidua. CONCLUSION: Amnion cells have the ability to produce beta-defensins. The beta3-defensin appears to be the predominant epithelial defensin expressed. Its induction by microbial mimics suggests that the amniotic epithelium may play a role in the innate immunity of the amniotic cavity.