PAQR4 regulates adipocyte function and systemic metabolic health by mediating ceramide levels.

PAQR4 is an orphan receptor in the PAQR family with an unknown function in metabolism. Here, we identify a critical role of PAQR4 in maintaining adipose tissue function and whole-body metabolic health. We demonstrate that expression of Paqr4 specifically in adipocytes, in an inducible and reversible fashion, leads to partial lipodystrophy, hyperglycaemia and hyperinsulinaemia, which is ameliorated by wild-type adipose tissue transplants or leptin treatment. By contrast, deletion of Paqr4 in adipocytes improves healthy adipose remodelling and glucose homoeostasis in diet-induced obesity. Mechanistically, PAQR4 regulates ceramide levels by mediating the stability of ceramide synthases (CERS2 and CERS5) and, thus, their activities. Overactivation of the PQAR4-CERS axis causes ceramide accumulation and impairs adipose tissue function through suppressing adipogenesis and triggering adipocyte de-differentiation. Blocking de novo ceramide biosynthesis rescues PAQR4-induced metabolic defects. Collectively, our findings suggest a critical function of PAQR4 in regulating cellular ceramide homoeostasis and targeting PAQR4 offers an approach for the treatment of metabolic disorders.

Adipose tissue fibrosis: the unwanted houseguest invited by obesity.

The prevalence of obesity is increasing exponentially across the globe. The lack of effective treatment options for long-term weight loss has magnified the enormity of this problem. Studies continue to demonstrate that adipose tissue holds a biological memory, one of the most important determinant of long-term weight maintenance. This phenomenon is consistent with the metabolically dynamic role of adipose tissue: it adapts and expands to store for excess energy and serves as an endocrine organ capable of synthesizing a number of biologically active molecules that regulate metabolic homeostasis. An important component of the plasticity of adipose tissue is the extracellular matrix, essential for structural support, mechanical stability, cell signaling and function. Chronic obesity upends a delicate balance of extracellular matrix synthesis and degradation, and the ECM accumulates in such a way that prevents the plasticity and function of the diverse cell types in adipose tissue. A series of maladaptive responses among the cells in adipose tissue leads to inflammation and fibrosis, major mechanisms that explain the link between obesity and insulin resistance, risk of type 2 diabetes, cardiovascular disease, and nonalcoholic fatty liver disease. Adipose tissue fibrosis persists after weight loss and further enhances adipose tissue dysfunction if weight is regained. Here, we highlight the current knowledge of the cellular events governing adipose tissue ECM remodeling during the development of obesity. Our goal is to delineate the relationship more clearly between adipose tissue ECM and metabolic disease, an important step toward better defining the pathophysiology of dysfunctional adipose tissue.

Adipose tissue macrophages exert systemic metabolic control by manipulating local iron concentrations.

Iron is essential to many fundamental biological processes, but its cellular compartmentalization and concentration must be tightly controlled. Although iron overload can contribute to obesity-associated metabolic deterioration, the subcellular localization and accumulation of iron in adipose tissue macrophages is largely unknown. Here, we show that macrophage mitochondrial iron levels control systemic metabolism in male mice by altering adipocyte iron concentrations. Using various transgenic mouse models to manipulate the macrophage mitochondrial matrix iron content in an inducible fashion, we demonstrate that lowering macrophage mitochondrial matrix iron increases numbers of M2-like macrophages in adipose tissue, lowers iron levels in adipocytes, attenuates inflammation and protects from high-fat-diet-induced metabolic deterioration. Conversely, elevating macrophage mitochondrial matrix iron increases M1-like macrophages and iron levels in adipocytes, exacerbates inflammation and worsens high-fat-diet-induced metabolic dysfunction. These phenotypes are robustly reproduced by transplantation of a small amount of fat from transgenic to wild-type mice. Taken together, we identify macrophage mitochondrial iron levels as a crucial determinant of systemic metabolic homeostasis in mice.

Adipocyte mesenchymal transition contributes to mammary tumor progression.

Obesity is associated with increased cancer incidence and progression. However, the relationship between adiposity and cancer remains poorly understood at the mechanistic level. Here, we report that adipocytes from tumor-invasive mammary fat undergo de-differentiation to fibroblast-like precursor cells during tumor progression and integrate into the tumor microenvironment. Single-cell sequencing reveals that these de-differentiated adipocytes lose their original identities and transform into multiple cell types, including myofibroblast- and macrophage-like cells, with their characteristic features involved in immune response, inflammation, and extracellular matrix remodeling. The de-differentiated cells are metabolically distinct from tumor-associated fibroblasts but exhibit comparable effects on tumor cell proliferation. Inducing de-differentiation by Xbp1s overexpression promotes tumor progression despite lower adiposity. In contrast, promoting lipid-storage capacity in adipocytes through MitoNEET overexpression curbs tumor growth despite greater adiposity. Collectively, the metabolic interplay between tumor cells and adipocytes induces adipocyte mesenchymal transition and contributes to reconfigure the stroma into a more tumor-friendly microenvironment.

Deficient Caveolin-1 Synthesis in Adipocytes Stimulates Systemic Insulin-Independent Glucose Uptake via Extracellular Vesicles.

Caveolin-1 (cav1) is an important structural and signaling component of plasma membrane invaginations called caveolae and is abundant in adipocytes. As previously reported, adipocyte-specific ablation of the cav1 gene (ad-cav1 knockout [KO] mouse) does not result in elimination of the protein, as cav1 protein traffics to adipocytes from neighboring endothelial cells. However, this mouse is a functional KO because adipocyte caveolar structures are depleted. Compared with controls, ad-cav1KO mice on a high-fat diet (HFD) display improved whole-body glucose clearance despite complete loss of glucose-stimulated insulin secretion, blunted insulin-stimulated AKT activation in metabolic tissues, and partial lipodystrophy. The cause is increased insulin-independent glucose uptake by white adipose tissue (AT) and reduced hepatic gluconeogenesis. Furthermore, HFD-fed ad-cav1KO mice display significant AT inflammation, fibrosis, mitochondrial dysfunction, and dysregulated lipid metabolism. The glucose clearance phenotype of the ad-cav1KO mice is at least partially mediated by AT small extracellular vesicles (AT-sEVs). Injection of control mice with AT-sEVs from ad-cav1KO mice phenocopies ad-cav1KO characteristics. Interestingly, AT-sEVs from ad-cav1KO mice propagate the phenotype of the AT to the liver. These data indicate that ad-cav1 is essential for healthy adaptation of the AT to overnutrition and prevents aberrant propagation of negative phenotypes to other organs by EVs.

Gut microbe-targeted choline trimethylamine lyase inhibition improves obesity via rewiring of host circadian rhythms.

Obesity has repeatedly been linked to reorganization of the gut microbiome, yet to this point obesity therapeutics have been targeted exclusively toward the human host. Here, we show that gut microbe-targeted inhibition of the trimethylamine N-oxide (TMAO) pathway protects mice against the metabolic disturbances associated with diet-induced obesity (DIO) or leptin deficiency (Lepob/ob). Small molecule inhibition of the gut microbial enzyme choline TMA-lyase (CutC) does not reduce food intake but is instead associated with alterations in the gut microbiome, improvement in glucose tolerance, and enhanced energy expenditure. We also show that gut microbial CutC inhibition is associated with reorganization of host circadian control of both phosphatidylcholine and energy metabolism. This study underscores the relationship between microbe and host metabolism and provides evidence that gut microbe-derived trimethylamine (TMA) is a key regulator of the host circadian clock. This work also demonstrates that gut microbe-targeted enzyme inhibitors have potential as anti-obesity therapeutics.

Extracellular vesicle-based interorgan transport of mitochondria from energetically stressed adipocytes.

Adipocytes undergo intense energetic stress in obesity resulting in loss of mitochondrial mass and function. We have found that adipocytes respond to mitochondrial stress by rapidly and robustly releasing small extracellular vesicles (sEVs). These sEVs contain respiration-competent, but oxidatively damaged mitochondrial particles, which enter circulation and are taken up by cardiomyocytes, where they trigger a burst of ROS. The result is compensatory antioxidant signaling in the heart that protects cardiomyocytes from acute oxidative stress, consistent with a preconditioning paradigm. As such, a single injection of sEVs from energetically stressed adipocytes limits cardiac ischemia/reperfusion injury in mice. This study provides the first description of functional mitochondrial transfer between tissues and the first vertebrate example of "inter-organ mitohormesis." Thus, these seemingly toxic adipocyte sEVs may provide a physiological avenue of potent cardio-protection against the inevitable lipotoxic or ischemic stresses elicited by obesity.

Adipose tissue hyaluronan production improves systemic glucose homeostasis and primes adipocytes for CL 316,243-stimulated lipolysis.

Plasma hyaluronan (HA) increases systemically in type 2 diabetes (T2D) and the HA synthesis inhibitor, 4-Methylumbelliferone, has been proposed to treat the disease. However, HA is also implicated in normal physiology. Therefore, we generated a Hyaluronan Synthase 2 transgenic mouse line, driven by a tet-response element promoter to understand the role of HA in systemic metabolism. To our surprise, adipocyte-specific overproduction of HA leads to smaller adipocytes and protects mice from high-fat-high-sucrose-diet-induced obesity and glucose intolerance. Adipocytes also have more free glycerol that can be released upon beta3 adrenergic stimulation. Improvements in glucose tolerance were not linked to increased plasma HA. Instead, an HA-driven systemic substrate redistribution and adipose tissue-liver crosstalk contributes to the systemic glucose improvements. In summary, we demonstrate an unexpected improvement in glucose metabolism as a consequence of HA overproduction in adipose tissue, which argues against the use of systemic HA synthesis inhibitors to treat obesity and T2D.

Adiponectin preserves metabolic fitness during aging.

Adiponectin is essential for the regulation of tissue substrate utilization and systemic insulin sensitivity. Clinical studies have suggested a positive association of circulating adiponectin with healthspan and lifespan. However, the direct effects of adiponectin on promoting healthspan and lifespan remain unexplored. Here, we are using an adiponectin null mouse and a transgenic adiponectin overexpression model. We directly assessed the effects of circulating adiponectin on the aging process and found that adiponectin null mice display exacerbated age-related glucose and lipid metabolism disorders. Moreover, adiponectin null mice have a significantly shortened lifespan on both chow and high-fat diet. In contrast, a transgenic mouse model with elevated circulating adiponectin levels has a dramatically improved systemic insulin sensitivity, reduced age-related tissue inflammation and fibrosis, and a prolonged healthspan and median lifespan. These results support a role of adiponectin as an essential regulator for healthspan and lifespan.

Mitochondrial metabolism is a key regulator of the fibro-inflammatory and adipogenic stromal subpopulations in white adipose tissue.

The adipose tissue stroma is a rich source of molecularly distinct stem and progenitor cell populations with diverse functions in metabolic regulation, adipogenesis, and inflammation. The ontology of these populations and the mechanisms that govern their behaviors in response to stimuli, such as overfeeding, however, are unclear. Here, we show that the developmental fates and functional properties of adipose platelet-derived growth factor receptor beta (PDGFRß)+ progenitor subpopulations are tightly regulated by mitochondrial metabolism. Reducing the mitochondrial ß-oxidative capacity of PDGFRß+ cells via inducible expression of MitoNEET drives a pro-inflammatory phenotype in adipose progenitors and alters lineage commitment. Furthermore, disrupting mitochondrial function in PDGFRß+ cells rapidly induces alterations in immune cell composition in lean mice and impacts expansion of adipose tissue in diet-induced obesity. The adverse effects on adipose tissue remodeling can be reversed by restoring mitochondrial activity in progenitors, suggesting therapeutic potential for targeting energy metabolism in these cells.

Dermal adipocytes contribute to the metabolic regulation of dermal fibroblasts.

Dermal fibroblasts are an essential population of skin cells. They are not only responsible for synthesis and remodelling of the extracellular matrix of the dermis, but also communicate with other skin cells via autocrine and paracrine interactions. Skin-associated dermal adipocytes reside below the reticular dermis. Strong lipolysis is observed during the regression of dermal adipocytes. However, the nature of the local intercellular crosstalk in which lipids released by dermal adipocytes affecting the metabolism of adjacent skin fibroblasts has not yet been examined. With the use of a series of novel mouse models that allow us to manipulate adipocytes, we demonstrate that dermal adipocytes can modulate the structure of the dermis through regulating extracellular matrix production in dermal fibroblasts. Fatty acids released by dermal adipocytes are involved in this process. Our observations offer new in vivo insights into the role of dermal adipocyte-derived lipids in influencing metabolism of adjacent local cells in the skin through a paracrine effect in the microenvironment of the dermal adipocyte.

Critical lipids link breastfeeding to healthy adipose tissue in infancy and adulthood.

The study of beige adipose tissue (BeAT) has recently gained popularity because of its potential as a therapeutic target for the treatment of obesity and other metabolic disorders. While BeAT regulation is well understood in adults, the critical signals regulating BeAT during infant development need to be better defined. The bioactive components in breast milk have been primarily studied in the context of immunity. In this issue of the JCI, Yu and Dilbaz et al. identify how a class of breast milk-specific lipid mediators referred to as alkylglycerols (AKGs) maintain BeAT in infants and prevent the transdifferentiation of BeAT into lipid-storing white adipose tissue (WAT).

The retinol-binding protein receptor STRA6 regulates diurnal insulin responses.

It has long been appreciated that insulin action is closely tied to circadian rhythms. However, the mechanisms that dictate diurnal insulin sensitivity in metabolic tissues are not well understood. Retinol-binding protein 4 (RBP4) has been implicated as a driver of insulin resistance in rodents and humans, and it has become an attractive drug target in type II diabetes. RBP4 is synthesized primarily in the liver where it binds retinol and transports it to tissues throughout the body. The retinol-RBP4 complex (holo-RBP) can be recognized by a cell-surface receptor known as stimulated by retinoic acid 6 (STRA6), which transports retinol into cells. Coupled to retinol transport, holo-RBP can activate STRA6-driven Janus kinase (JAK) signaling and downstream induction of signal transducer and activator of transcription (STAT) target genes. STRA6 signaling in white adipose tissue has been shown to inhibit insulin receptor responses. Here, we examined diurnal rhythmicity of the RBP4/STRA6 signaling axis and investigated whether STRA6 is necessary for diurnal variations in insulin sensitivity. We show that adipose tissue STRA6 undergoes circadian patterning driven in part by the nuclear transcription factor REV-ERBα. Furthermore, STRA6 is necessary for diurnal rhythmicity of insulin action and JAK/STAT signaling in adipose tissue. These findings establish that holo-RBP and its receptor STRA6 are potent regulators of diurnal insulin responses and suggest that the holo-RBP/STRA6 signaling axis may represent a novel therapeutic target in type II diabetes.

The role of different methods of nerve ablation in prevention of neuroma.

BACKGROUND: The aim of this study was to compare the incidence of neuroma formation and neuropathic pain following different techniques of nerve ablation in a rat sural nerve model. METHODS: Rat sural nerve was subjected to four different techniques of ablation with standardized creation of a 1-cm gap (n = 15 in each group). These included nerve avulsion, transection and burying in muscle, transection and folding of nerve, and transection alone. Animals were killed after 3 months. Explanted nerves were sectioned and stained with Masson trichrome and S-100 stain against neural tissue. The maximal neural cross-sectional area and neural-to-connective tissue ratio was quantified. Quantitative reverse-transcriptase polymerase chain reaction (n = 5) was used to analyze relative mRNA expression of ciliary neurotrophic factor and calcitonin gene-related peptide. RESULTS: Neural cross-sectional area was statistically increased (p < 0.05) compared with controls in folded, muscle buried, and transected specimens but decreased in avulsed specimens. The neural-to-connective tissue ratio was statistically decreased in the avulsed group. Relative mRNA expression of ciliary neurotrophic factor was lowest in muscle buried (4 percent of control) (p < 0.05) and avulsed specimens (15 percent of control) (p < 0.05) and higher in folded (52 percent of control) and transected specimens (75 percent of control). Relative mRNA expression of calcitonin gene-related peptide was highest in folded specimens (302 percent of control) (p < 0.05). CONCLUSIONS: Folding and transection lead to increased histologic evidence of neuroma formation, whereas folding leads to neuropathic pain, assayed by calcitonin gene-related peptide expression. Avulsion and muscle burying are preferable techniques for nerve ablation and inhibit nerve regeneration, evidenced by decreased ciliary neurotrophic factor expression. Avulsion offers an alternative to muscle burying when there is no muscle in the vicinity to bury the transected nerve.

The contribution of endogenous and exogenous factors to male alopecia: a study of identical twins.

BACKGROUND: The purpose of this study was to investigate the potential contribution of environmental factors and testosterone on male alopecia. METHODS: Ninety-two identical male twins were recruited from 2009 to 2011. A comprehensive questionnaire was completed followed by the acquisition of sputum samples for testosterone analysis and standardized digital photography. Frontal, temporal, and vertex hair loss was assessed from these photographs. Hair loss was then correlated with survey responses and testosterone levels between twin pairs. Two independent, blinded observers also rated the photographs for hair thinning. RESULTS: Increased smoking duration (p < 0.001) and the presence of dandruff (p = 0.028) were significantly associated with increased frontal hair loss. Increased exercise duration (p = 0.002), consumption of more than four alcoholic drinks per week (p = 0.042), and increased money spent on hair loss products (p = 0.050) were all associated with increased temporal hair loss. Daily hat use (p = 0.050), higher body mass index (p = 0.012), and higher testosterone levels (p = 0.040) were associated with decreased temporal hair loss. Factors that were significantly associated with increased vertex hair loss included abstinence from alcohol consumption (p = 0.030), consumption of more than four alcoholic drinks per week (p = 0.004), increased smoking duration (p = 0.047), increased exercise duration (p = 0.050), and increased stress duration (p = 0.010). Lower body mass index, more children, increased caffeine consumption, history of skin disease, and abstinence from alcohol were significantly associated with increased hair thinning scores (p < 0.05). CONCLUSION: This study offers substantial evidence that exogenous factors may have a clinically significant impact on hair loss. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, III.

The contribution of endogenous and exogenous factors to female alopecia: a study of identical twins.

BACKGROUND: In this study, the authors investigated the potential contribution of environmental factors and testosterone levels on androgenic alopecia in women. METHODS: Ninety-eight identical female twins were recruited from 2009 to 2011. Subjects were asked to complete a comprehensive questionnaire, provide a sputum sample for testosterone analysis, and pose for standardized digital photography. Frontal, temporal, and vertex hair loss were assessed from the photographs using Adobe Photoshop. Hair loss measures were then correlated with survey responses and testosterone levels between twin pairs. Two independent, blinded observers also rated the photographs for hair thinning. RESULTS: Factors associated with increased frontal hair loss included multiple marriages (p = 0.043); longer sleep duration (p = 0.011); higher severity of stress (p = 0.034); positive smoking history (p = 0.021); higher income (p = 0.023); absence of hat use (p = 0.017); and history of diabetes mellitus (p = 0.023), polycystic ovarian syndrome (p = 0.002), and hypertension (p = 0.001). Factors associated with increased temporal hair loss included divorce or separation (p = 0.034), multiple marriages (p = 0.040), more children (p = 0.005), longer sleep duration (p = 0.006), and history of diabetes mellitus (p = 0.008) and hypertension (p = 0.027). Lack of sun protection (p = 0.020), consuming less caffeine (p = 0.040), history of skin disease (p = 0.048), and lack of exercise (p = 0.012) were associated with increased vertex hair loss. Higher testosterone levels were associated with increased temporal and vertex hair loss patterns (p < 0.039). Increased stress, increased smoking, having more children, and having a history of hypertension and cancer were all associated with increased hair thinning (p < 0.05). CONCLUSION: This study implicates several environmental risk factors in the pathophysiology of female alopecia.

Stromal-cell-derived factor (SDF) 1-alpha in combination with BMP-2 and TGF-ß1 induces site-directed cell homing and osteogenic and chondrogenic differentiation for tissue engineering without the requirement for cell seeding.

The clinical translation of tissue engineering approaches is limited by the requirement of a cell source. Cell guidance is a new concept that provides an alternative approach, obviating a requirement for an external cell source. This relies on site-specific homing and differentiation of the patient's own cells to an implanted scaffold through controlled delivery of cytokines. In this study, we used stromal-cell-derived factor 1-alpha (SDF-1α) in combination with bone morphogenic protein (BMP)-2 or transforming growth factor (TGF)-ß1 to induce cell migration and osteogenic or chondrogenic differentiation, respectively, in implanted scaffolds in a rat model. A customized cytokine microdelivery apparatus was used to ensure the constant rate and concentration of cytokine delivery around the scaffold. The formation of osteoid or early cartilage was observed after 4 weeks in specimens treated with SDF-1α and either BMP-2 or TGF-ß1. The density of cellular infiltrate and formation of differentiated tissue were lower in scaffolds treated only with BMP-2 or TGF-ß1. Thus, controlled SDF-1α delivery induces cell migration into scaffolds and can result in enhanced osteogenesis and chondrogenesis when used in combination with differentiation cytokines for purposes of tissue engineering.

Propranolol induces regression of hemangioma cells through HIF-1α-mediated inhibition of VEGF-A.

OBJECTIVE: To investigate the mechanism of propranolol on regression of infantile hemangiomas. BACKGROUND: Propranolol has been found to be effective in treatment of severe hemangiomas of infancy. However, its mechanism of action is as yet unknown. METHODS: Cultured proliferating and involuting hemangioma endothelial cells were treated with varying concentrations of propranolol for up to 4 days. Analysis was performed using cell viability, migration, and tubulogenesis assays, as well as quantitative RT-PCR and flow cytometry. Western blots and ELISA assays were used to assess protein expression. RESULTS: Treatment with propranolol led to a dose dependent cytotoxic effect in hemangioma endothelial cells with decreased cell viability, migration, and tubulogenesis. This cytotoxic effect was VEGF (vascular endothelial growth factor) dependent, as demonstrated by decreased VEGF, VEGF-R1, and VEGF-R2 production. Decreased signaling through the VEGF pathway resulted in downregulation of PI3/Akt and p38/MAPK activity. Decreased VEGF activity was mediated through the hypoxia inducible factor (HIF)-1α pathway but not through NF-κß signaling. CONCLUSIONS: Collectively, these data suggest that propranolol exerts its suppressive effects on hemangiomas through the HIF-1α-VEGF-A angiogenesis axis, with effects mediated through the PI3/Akt and p38/MAPK pathways. These findings provide a plausible mechanism of action of propranolol on regression of infantile hemangiomas.