CTRP6 promotes the macrophage inflammatory response, and its deficiency attenuates LPS-induced inflammation.

Macrophages play critical roles in inflammation and tissue homeostasis, and their functions are regulated by various autocrine, paracrine, and endocrine factors. We have previously shown that CTRP6, a secreted protein of the C1q family, targets both adipocytes and macrophages to promote obesity-linked inflammation. However, the gene programs and signaling pathways directly regulated by CTRP6 in macrophages remain unknown. Here, we combine transcriptomic and phosphoproteomic analyses to show that CTRP6 activates inflammatory gene programs and signaling pathways in mouse bone marrow-derived macrophages (BMDMs). Treatment of BMDMs with CTRP6 upregulated proinflammatory, and suppressed the antiinflammatory, gene expression. We also showed that CTRP6 activates p44/42-MAPK, p38-MAPK, and NF-κB signaling pathways to promote inflammatory cytokine secretion from BMDMs, and that pharmacologic inhibition of these signaling pathways markedly attenuated the effects of CTRP6. Pretreatment of BMDMs with CTRP6 also sensitized and potentiated the BMDMs response to lipopolysaccharide (LPS)-induced inflammatory signaling and cytokine secretion. Consistent with the metabolic phenotype of proinflammatory macrophages, CTRP6 treatment induced a shift toward aerobic glycolysis and lactate production, reduced oxidative metabolism, and elevated mitochondrial reactive oxygen species production in BMDMs. Importantly, in accordance with our in vitro findings, BMDMs from CTRP6-deficient mice were less inflammatory at baseline and showed a marked suppression of LPS-induced inflammatory gene expression and cytokine secretion. Finally, loss of CTRP6 in mice also dampened LPS-induced inflammation and hypothermia. Collectively, our findings suggest that CTRP6 regulates and primes the macrophage response to inflammatory stimuli and thus may have a role in modulating tissue inflammatory tone in different physiological and disease contexts.

CTRP11 contributes modestly to systemic metabolism and energy balance.

C1q/TNF-related proteins (CTRP1-15) constitute a conserved group of secreted proteins of the C1q family with diverse functions. In vitro studies have shown that CTRP11/C1QL4 can inhibit adipogenesis, antagonize myoblast fusion, and promote testosterone synthesis and secretion. Whether CTRP11 is required for these processes in vivo remains unknown. Here, we show that knockout (KO) mice lacking CTRP11 have normal skeletal muscle mass and function, and testosterone level, suggesting that CTRP11 is dispensable for skeletal muscle development and testosterone production. We focused our analysis on whether this nutrient-responsive secreted protein plays a role in controlling sugar and fat metabolism. At baseline when mice are fed a standard chow, CTRP11 deficiency affects metabolic parameters in a sexually dimorphic manner. Only Ctrp11-KO female mice have significantly higher fasting serum ketones and reduced physical activity. In the refeeding phase following food withdrawal, Ctrp11-KO female mice have reduced food intake and increased metabolic rate and energy expenditure, highlighting CTRP11's role in fasting-refeeding response. When challenged with a high-fat diet to induce obesity and metabolic dysfunction, CTRP11 deficiency modestly exacerbates obesity-induced glucose intolerance, with more pronounced effects seen in Ctrp11-KO male mice. Switching to a low-fat diet after obesity induction results in greater fat loss in wild type relative to KO male mice, suggesting impaired response to obesity reversal and reduced metabolic flexibility in the absence of CTRP11. Collectively, our data provide genetic evidence for novel sex-dependent metabolic regulation by CTRP11, but note the overall modest contribution of CTRP11 to systemic energy homeostasis.

CTRP14 inactivation alters physical activity and food intake response to fasting and refeeding.

Secreted proteins of the C1q/TNF-related protein (CTRP) family play diverse functions in different organ systems. In the brain, CTRP14/C1QL1 is required for the proper establishment and maintenance of synapses between climbing fibers and cerebellar Purkinje cells. Beyond the central nervous system, the function of CTRP14 is largely unknown. A recent genome-wide association study has implicated CTRP14/C1QL1 as a candidate gene associated with total body fat mass. Here, we explored the potential metabolic roles of CTRP14. We show that Ctrp14 expression in peripheral tissues is dynamically regulated by fasting-refeeding and high-fat feeding. In the chow-fed basal state, Ctrp14 deletion modestly reduces glucose tolerance in knockout (KO) male mice and affects physical activity in a sex- and nutritional state-dependent manner. In the ad libitum fed state, Ctrp14 KO male mice have lower physical activity. In contrast, female KO mice have increased physical activity in the fasted and refed states. In response to an obesogenic diet, CTRP14-deficient mice of either sex gained similar weight and are indistinguishable from wild-type littermates in body composition, lipid profiles, and insulin sensitivity. Ambulatory activity, however, is reduced in Ctrp14 KO male mice. Food intake is also reduced in Ctrp14 KO male mice in the refed period following food deprivation. Meal pattern analyses indicate that decreased caloric intake from fasting to refeeding is due, in part, to smaller meal size. We conclude that CTRP14 is largely dispensable for metabolic homeostasis, but highlight context-dependent and sexually dimorphic metabolic responses of Ctrp14 deletion affecting physical activity and ingestive behaviors.NEW & NOTEWORTHY CTRP14 is a secreted protein whose function in the peripheral tissues is largely unknown. We show that the expression of Ctrp14 in peripheral tissues is regulated by metabolic and nutritional state. We generated mice lacking CTRP14 and show that CTRP14 deficiency alters physical activity and food intake in response to fasting and refeeding. Our data has provided new and valuable information on the physiological function of CTRP14.

CTRP4 ablation impairs associative learning and memory.

C1q/TNF-related protein (CTRP) family comprises fifteen highly conserved secretory proteins with diverse central and peripheral functions. In zebrafish, mouse, and human, CTRP4 is most highly expressed in the brain. We previously showed that CTRP4 is a metabolically responsive regulator of food intake and energy balance, and mice lacking CTRP4 exhibit sexually dimorphic changes in ingestive behaviors and systemic metabolism. Recent single-cell RNA sequencing also revealed Ctrp4/C1qtnf4 expression in diverse neuronal cell types across distinct anatomical brain regions, hinting at additional roles in the central nervous system not previously characterized. To uncover additional central functions of CTRP4, we subjected Ctrp4 knockout (KO) mice to a battery of behavioral tests. Relative to wild-type (WT) littermates, loss of CTRP4 does not alter exploratory, anxiety-, or depressive-like behaviors, motor function and balance, sensorimotor gating, novel object recognition, and spatial memory. While pain-sensing mechanisms in response to thermal stress and mild shock are intact, both male and female Ctrp4 KO mice have increased sensitivity to pain induced by higher-level shock, suggesting altered nociceptive function. Importantly, CTRP4 deficiency impairs hippocampal-dependent associative learning and memory as assessed by trace fear conditioning paradigm. This deficit is sex-dependent, affects only female mice, and is associated with altered expression of learning and memory genes (Arc, c-fos, and Pde4d) in the hippocampus and cortex. Altogether, our behavioral and gene expression analyses have uncovered novel aspects of the CTRP4 function and provided a physiological context to further investigate its mechanism of action in the central and peripheral nervous system.

Local shifts in inflammatory and resolving lipid mediators in response to tendon overuse.

Tendon inflammation has been implicated in both adaptive connective tissue remodeling and overuse-induced tendinopathy. Lipid mediators control both the initiation and resolution of inflammation, but their roles within tendon are largely unknown. Here, we profiled local shifts in intratendinous lipid mediators via liquid chromatography-tandem mass spectrometry in response to synergist ablation-induced plantaris tendon overuse. Sixty-four individual lipid mediators were detected in homogenates of plantaris tendons from ambulatory control rats. This included many bioactive metabolites of the cyclooxygenase (COX), lipoxygenase (LOX), and epoxygenase (CYP) pathways. Synergist ablation induced a robust inflammatory response at day 3 post-surgery characterized by epitenon infiltration of polymorphonuclear leukocytes and monocytes/macrophages (MΦ), heightened expression of inflammation-related genes, and increased intratendinous concentrations of the pro-inflammatory eicosanoids thromboxane B2 and prostaglandin E2 . By day 7, MΦ became the predominant myeloid cell type in tendon and there were further delayed increases in other COX metabolites including prostaglandins D2 , F2α , and I2 . Specialized pro-resolving mediators including protectin D1, resolvin D2 and D6, as well as related pathway markers of D-resolvins (17-hydroxy-docosahexaenoic acid), E-resolvins (18-hydroxy-eicosapentaenoic acid), and lipoxins (15-hydroxy-eicosatetraenoic acid) were also increased locally in response to tendon overuse, as were anti-inflammatory fatty acid epoxides of the CYP pathway (eg, epoxy-eicosatrienoic acids). Nevertheless, intratendinous prostaglandins remained markedly increased even following 28 days of tendon overuse together with a lingering MΦ presence. These data reveal a delayed and prolonged local inflammatory response to tendon overuse characterized by an overwhelming predominance of pro-inflammatory eicosanoids and a relative lack of specialized pro-resolving lipid mediators.

Altered adipokines in obese adolescents: a cross-sectional and longitudinal analysis across the spectrum of glycemia.

Obesity and type 2 diabetes are rapidly increasing in the adolescent population. We sought to determine whether adipokines, specifically leptin, C1q/TNF-related proteins 1 (CTRP1) and CTRP9, and the hepatokine fibroblast growth factor 21 (FGF21), are associated with obesity and hyperglycemia in a cohort of lean and obese adolescents, across the spectrum of glycemia. In an observational, longitudinal study of lean and obese adolescents, we measured fasting laboratory tests, oral glucose tolerance tests, and adipokines including leptin, CTRP1, CTRP9, and FGF21. Participants completed baseline and 2-year follow-up study visits and were categorized as lean (LC, lean control; n = 30), obese normoglycemic (ONG; n = 61), and obese hyperglycemic (OHG; n = 31) adolescents at baseline and lean (n = 8), ONG (n = 18), and OHG (n = 4) at follow-up. Groups were compared using ANOVA and regression analysis, and linear mixed effects modeling was used to test for differences in adipokine levels across baseline and follow-up visits. Results showed that at baseline, leptin was higher in all obese groups (P < 0.001) compared with LC. FGF21 was higher in OHG participants compared with LC (P < 0.001) and ONG (P < 0.001) and positively associated with fasting glucose (P < 0.001), fasting insulin (P < 0.001), Homeostasis Model Assessment-Insulin Resistance Index (HOMA-IR; P < 0.001), and hemoglobin A1c (HbA1c; P = 0.01). CTRP1 was higher in OHG compared with ONG (P = 0.03). CTRP9 was not associated with obesity or hyperglycemia in this pediatric cohort. At 2 years, leptin decreased in ONG (P = 0.003) and FGF21 increased in OHG (P = 0.02), relative to lean controls. Altered adipokine levels are associated with the inflammatory milieu in obese youth with and without hyperglycemia. In adolescence, the novel adipokine CTRP1 was elevated with hyperglycemia, whereas CTRP9 was unchanged in this cohort.NEW & NOTEWORTHY Leptin is higher in obese adolescents and FGF21 is higher in obese hyperglycemic adolescents. The novel adipokine CTRP1 is higher in obese hyperglycemic adolescents, whereas CTRP9 was unchanged in this adolescent cohort.

Obesity alters Ace2 and Tmprss2 expression in lung, trachea, and esophagus in a sex-dependent manner: Implications for COVID-19.

Obesity is a major risk factor for SARS-CoV-2 infection and COVID-19 severity. The underlying basis of this association is likely complex in nature. The host-cell receptor angiotensin converting enzyme 2 (ACE2) and the type II transmembrane serine protease (TMPRSS2) are important for viral cell entry. It is unclear whether obesity alters expression of Ace2 and Tmprss2 in the lower respiratory tract. Here, we show that: 1) Ace2 expression is elevated in the lung and trachea of diet-induced obese male mice and reduced in the esophagus of obese female mice relative to lean controls; 2) Tmprss2 expression is increased in the trachea of obese male mice but reduced in the lung and elevated in the trachea of obese female mice relative to lean controls; 3) in chow-fed lean mice, females have higher expression of Ace2 in the lung and esophagus as well as higher Tmprss2 expression in the lung but lower expression in the trachea compared to males; and 4) in diet-induced obese mice, males have higher expression of Ace2 in the trachea and higher expression of Tmprss2 in the lung compared to females, whereas females have higher expression of Tmprss2 in the trachea relative to males. Our data indicate diet- and sex-dependent modulation of Ace2 and Tmprss2 expression in the lower respiratory tract and esophagus. Given the high prevalence of obesity worldwide and a sex-biased mortality rate, we discuss the implications and relevance of our results for COVID-19.

Aging and chronic high-fat feeding negatively affect kidney size, function, and gene expression in CTRP1-deficient mice.

C1q/TNF-related protein 1 (CTRP1) is an endocrine factor with metabolic, cardiovascular, and renal functions. We previously showed that aged Ctrp1-knockout (KO) mice fed a control low-fat diet develop renal hypertrophy and dysfunction. Since aging and obesity adversely affect various organ systems, we hypothesized that aging, in combination with obesity induced by chronic high-fat feeding, would further exacerbate renal dysfunction in CTRP1-deficient animals. To test this, we fed wild-type and Ctrp1-KO mice a high-fat diet for 8 mo or longer. Contrary to our expectation, no differences were observed in blood pressure, heart function, or vascular stiffness between genotypes. Loss of CTRP1, however, resulted in an approximately twofold renal enlargement (relative to body weight), ∼60% increase in urinary total protein content, and elevated pH, and changes in renal gene expression affecting metabolism, signaling, transcription, cell adhesion, solute and metabolite transport, and inflammation. Assessment of glomerular integrity, the extent of podocyte foot process effacement, as well as renal response to water restriction and salt loading did not reveal significant differences between genotypes. Interestingly, blood platelet, white blood cell, neutrophil, lymphocyte, and eosinophil counts were significantly elevated, whereas mean corpuscular volume and hemoglobin were reduced in Ctrp1-KO mice. Cytokine profiling revealed increased circulating levels of CCL17 and TIMP-1 in KO mice. Compared with our previous study, current data suggest that chronic high-fat feeding affects renal phenotypes differently than similarly aged mice fed a control low-fat diet, highlighting a diet-dependent contribution of CTRP1 deficiency to age-related changes in renal structure and function.

Ontogenetic and in silico models of spatial-packing in the hypermuscular mouse skull.

Networks linking single genes to multiple phenotypic outcomes can be founded on local anatomical interactions as well as on systemic factors like biochemical products. Here we explore the effects of such interactions by investigating the competing spatial demands of brain and masticatory muscle growth within the hypermuscular myostatin-deficient mouse model and in computational simulations. Mice that lacked both copies of the myostatin gene (-/-) and display gross hypermuscularity, and control mice that had both copies of the myostatin gene (+/+) were sampled at 1, 7, 14 and 28 postnatal days. A total of 48 mice were imaged with standard as well as contrast-enhanced microCT. Size metrics and landmark configurations were collected from the image data and were analysed alongside in silico models of tissue expansion. Findings revealed that: masseter muscle volume was smaller in -/- mice at day 1 but became, and remained thereafter, larger by 7 days; -/- endocranial volumes begin and remained smaller; -/- enlargement of the masticatory muscles was associated with caudolateral displacement of the calvarium, lateral displacement of the zygomatic arches, and slight dorsal deflection of the face and basicranium. Simulations revealed basicranial retroflexion (flattening) and dorsal deflection of the face associated with muscle expansion and abrogative covariations of basicranial flexion and ventral facial deflection associated with endocranial expansion. Our findings support the spatial-packing theory and highlight the importance of understanding the harmony of competing spatial demands that can shape and maintain mammalian skull architecture during ontogeny.

Multiomics analysis of the mdx/mTR mouse model of Duchenne muscular dystrophy.

PURPOSE/AIM: Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disease characterized by extensive muscle weakness. Patients with DMD lack a functional dystrophin protein, which transmits force and organizes the cytoskeleton of skeletal muscle. Multiomic studies have been proposed as a way to obtain novel insight about disease processes from preclinical models, and we used this approach to study pathological changes in dystrophic muscles. MATERIALS AND METHODS: We evaluated hindlimb muscles of male mdx/mTR mice, which lack a functional dystrophin protein and have deficits in satellite cell abundance and proliferative capacity. Wild type (WT) C57BL/6 J mice served as controls. Muscle fiber contractility was measured, along with changes in the transcriptome using RNA sequencing, and in the proteome, metabolome, and lipidome using mass spectrometry. RESULTS: While mdx/mTR mice displayed gross pathological changes and continued cycles of degeneration and regeneration, we found no differences in permeabilized fiber contractility between strains. However, there were numerous changes in the transcriptome and proteome related to protein balance, contractile elements, extracellular matrix, and metabolism. There was only a 53% agreement in fold-change data between the proteome and transcriptome. Numerous changes in markers of skeletal muscle metabolism were observed, with dystrophic muscles exhibiting elevated glycolytic metabolites such as 6-phosphoglycerate, fructose-6-phosphate and glucose-6-phosphate, fructose bisphosphate, phosphorylated hexoses, and phosphoenolpyruvate. CONCLUSIONS: These findings highlight the utility of multiomics in studying muscle disease, and provide additional insight into the pathological changes in dystrophic muscles that might help to indirectly guide evidence-based nutritional or exercise prescription in DMD patients.

Loss of CTRP4 alters adiposity and food intake behaviors in obese mice.

Central and peripheral mechanisms are both required for proper control of energy homeostasis. Among circulating plasma proteins, C1q/TNF-related proteins (CTRPs) have recently emerged as important regulators of sugar and fat metabolism. CTRP4, expressed in brain and adipose tissue, is unique among the family members in having two tandem globular C1q domains. We previously showed that central administration of recombinant CTRP4 suppresses food intake, suggesting a central nervous system role in regulating ingestive physiology. Whether this effect is pharmacological or physiological remains unclear. We used a loss-of-function knockout (KO) mouse model to clarify the physiological role of CTRP4. Under basal conditions, CTRP4 deficiency increased serum cholesterol levels and impaired glucose tolerance in male but not female mice fed a control low-fat diet. When challenged with a high-fat diet, male and female KO mice responded differently to weight gain and had different food intake patterns. On an obesogenic diet, male KO mice had similar weight gain as wild-type littermates. When fed ad libitum, KO male mice had greater meal number, shorter intermeal interval, and reduced satiety ratio. Female KO mice, in contrast, had lower body weight and adiposity. In the refeeding period following food deprivation, female KO mice had significantly higher food intake due to longer meal duration and reduced satiety ratio. Collectively, our data provide genetic evidence for a sex-dependent physiological role of CTRP4 in modulating food intake patterns and systemic energy metabolism.

CTRP12 ablation differentially affects energy expenditure, body weight, and insulin sensitivity in male and female mice.

Secreted hormones facilitate tissue cross talk to maintain energy balance. We previously described C1q/TNF-related protein 12 (CTRP12) as a novel metabolic hormone. Gain-of-function and partial-deficiency mouse models have highlighted important roles for this fat-derived adipokine in modulating systemic metabolism. Whether CTRP12 is essential and required for metabolic homeostasis is unknown. We show here that homozygous deletion of Ctrp12 gene results in sexually dimorphic phenotypes. Under basal conditions, complete loss of CTRP12 had little impact on male mice, whereas it decreased body weight (driven by reduced lean mass and liver weight) and improved insulin sensitivity in female mice. When challenged with a high-fat diet, Ctrp12 knockout (KO) male mice had decreased energy expenditure, increased weight gain and adiposity, elevated serum TNFα level, and reduced insulin sensitivity. In contrast, female KO mice had reduced weight gain and liver weight. The expression of lipid synthesis and catabolism genes, as well as profibrotic, endoplasmic reticulum stress, and oxidative stress genes were largely unaffected in the adipose tissue of Ctrp12 KO male mice. Despite greater adiposity and insulin resistance, Ctrp12 KO male mice fed an obesogenic diet had lower circulating triglyceride and free fatty acid levels. In contrast, lipid profiles of the leaner female KO mice were not different from those of WT controls. These data suggest that CTRP12 contributes to whole body energy metabolism in genotype-, diet-, and sex-dependent manners, underscoring complex gene-environment interactions influencing metabolic outcomes.

PRADC1: a novel metabolic-responsive secretory protein that modulates physical activity and adiposity.

Interorgan communication mediated by secreted proteins plays a pivotal role in metabolic homeostasis, yet the function of many circulating secretory proteins remains unknown. Here, we describe the function of protease-associated domain-containing 1 (PRADC1), an enigmatic secretory protein widely expressed in humans and mice. In metabolically active tissues (liver, muscle, fat, heart, and kidney), we showed that Pradc1 expression is significantly suppressed by refeeding and reduced in kidney and brown fat in the context of obesity. PRADC1 is dispensable for whole-body metabolism when mice are fed a low-fat diet. However, in obesity induced by high-fat feeding, PRADC1-deficient female mice have reduced weight gain and adiposity despite similar caloric intake. Decreased fat mass is attributed, in part, to increased metabolic rate, physical activity, and energy expenditure in these animals. Reduced adiposity in PRADC1-deficient mice, however, does not improve systemic glucose and lipid metabolism, insulin sensitivity, liver steatosis, or adipose inflammation. Thus, in PRADC1-deficient animals, decreased fat mass and enhanced physical activity are insufficient to confer a healthy metabolic phenotype in the context of an obesogenic diet. Our results shed light on the physiologic function of PRADC1 and the complex regulation of metabolic health.-Rodriguez, S., Stewart, A. N., Lei, X., Cao, X., Little, H. C., Fong, V., Sarver, D. C., Wong, G. W. PRADC1: a novel metabolic-responsive secretory protein that modulates physical activity and adiposity.

Insulin-like growth factor 1 signaling in tenocytes is required for adult tendon growth.

Tenocytes serve to synthesize and maintain collagen fibrils and other extracellular matrix proteins in tendon. Despite the high prevalence of tendon injury, the underlying biologic mechanisms of postnatal tendon growth and repair are not well understood. IGF1 plays an important role in the growth and remodeling of numerous tissues but less is known about IGF1 in tendon. We hypothesized that IGF1 signaling is required for proper tendon growth in response to mechanical loading through regulation of collagen synthesis and cell proliferation. To test this hypothesis, we conditionally deleted the IGF1 receptor (IGF1R) in scleraxis (Scx)-expressing tenocytes using a tamoxifen-inducible Cre-recombinase system and caused tendon growth in adult mice via mechanical overload of the plantaris tendon. Compared with control Scx-expressing IGF1R-positive (Scx:IGF1R+) mice, in which IGF1R is present in tenocytes, mice that lacked IGF1R in their tenocytes [Scx-expressing IGF1R-negative (Scx:IGF1RΔ) mice] demonstrated reduced cell proliferation and smaller tendons in response to mechanical loading. Additionally, we identified that both the PI3K/protein kinase B and ERK pathways are activated downstream of IGF1 and interact in a coordinated manner to regulate cell proliferation and protein synthesis. These studies indicate that IGF1 signaling is required for proper postnatal tendon growth and support the potential use of IGF1 in the treatment of tendon disorders.-Disser, N. P., Sugg, K. B., Talarek, J. R., Sarver, D. C., Rourke, B. J., Mendias, C. L. Insulin-like growth factor 1 signaling in tenocytes is required for adult tendon growth.

Myonectin deletion promotes adipose fat storage and reduces liver steatosis.

We recently described myonectin (also known as erythroferrone) as a novel skeletal muscle-derived myokine with metabolic functions. Here, we use a genetic mouse model to determine myonectin's requirement for metabolic homeostasis. Female myonectin-deficient mice had larger gonadal fat pads and developed mild insulin resistance when fed a high-fat diet (HFD) and had reduced food intake during refeeding after an unfed period but were otherwise indistinguishable from wild-type littermates. Male mice lacking myonectin, however, had reduced physical activity when fed ad libitum and in the postprandial state but not during the unfed period. When stressed with an HFD, myonectin-knockout male mice had significantly elevated VLDL-triglyceride (TG) and strikingly impaired lipid clearance from circulation following an oral lipid load. Fat distribution between adipose and liver was also altered in myonectin-deficient male mice fed an HFD. Greater fat storage resulted in significantly enlarged adipocytes and was associated with increased postprandial lipoprotein lipase activity in adipose tissue. Parallel to this was a striking reduction in liver steatosis due to significantly reduced TG accumulation. Liver metabolite profiling revealed additional significant changes in bile acids and 1-carbon metabolism pathways. Combined, our data affirm the physiologic importance of myonectin in regulating local and systemic lipid metabolism.-Little, H. C., Rodriguez, S., Lei, X., Tan, S. Y., Stewart, A. N., Sahagun, A., Sarver, D. C., Wong, G. W. Myonectin deletion promotes adipose fat storage and reduces liver steatosis.

Characterizing novel olfactory receptors expressed in the murine renal cortex.

The kidney uses specialized G protein-coupled receptors, including olfactory receptors (ORs), to act as sensors of molecules and metabolites. In the present study, we cloned and studied seven renal ORs, which we previously found to be expressed in the murine renal cortex. As most ORs are orphan receptors, our goal was to identify ligands for these ORs in the hope that this will guide future research into their functional roles. We identified novel ligands for two ORs: Olfr558 and Olfr90. For Olfr558, we confirmed activation by previously reported ligands and identified 16 additional carboxylic acids that activated this OR. The strongest activation of Olfr558 was produced by butyric, cyclobutanecarboxylic, isovaleric, 2-methylvaleric, 3-methylvaleric, 4-methylvaleric, and valeric acids. The primary in vivo source of both butyric and isovaleric acids is gut microbial metabolism. We also identified 14 novel ligands that activated Olfr90, the strongest of which were 2-methyl-4-propyl-1,3-oxathiane, 1-octen-3-ol, 2-octanol, and 3-octanol. Interestingly, 8 of these 14 ligands are of fungal origin. We also investigated the tissue distribution of these receptors and found that they are each found in a subset of "nonsensory" tissues. Finally, we examined the putative human orthologs of Olfr558 and Olfr90 and found that the human ortholog of Olfr558 (OR51E1) has a similar ligand profile, indicating that the role of this OR is likely evolutionarily conserved. In summary, we examined seven novel renal ORs and identified new ligands for Olfr558 and Olfr90, which imply that both of these receptors serve to detect metabolites produced by microorganisms.

Postnatal tendon growth and remodeling require platelet-derived growth factor receptor signaling.

Platelet-derived growth factor receptor (PDGFR) signaling plays an important role in the fundamental biological activities of many cells that compose musculoskeletal tissues. However, little is known about the role of PDGFR signaling during tendon growth and remodeling in adult animals. Using the hindlimb synergist ablation model of tendon growth, our objectives were to determine the role of PDGFR signaling in the adaptation of tendons subjected to a mechanical growth stimulus, as well as to investigate the biological mechanisms behind this response. We demonstrate that both PDGFRs, PDGFRα and PDGFRß, are expressed in tendon fibroblasts and that the inhibition of PDGFR signaling suppresses the normal growth of tendon tissue in response to mechanical growth cues due to defects in fibroblast proliferation and migration. We also identify membrane type-1 matrix metalloproteinase (MT1-MMP) as an essential proteinase for the migration of tendon fibroblasts through their extracellular matrix. Furthermore, we report that MT1-MMP translation is regulated by phosphoinositide 3-kinase/Akt signaling, while ERK1/2 controls posttranslational trafficking of MT1-MMP to the plasma membrane of tendon fibroblasts. Taken together, these findings demonstrate that PDGFR signaling is necessary for postnatal tendon growth and remodeling and that MT1-MMP is a critical mediator of tendon fibroblast migration and a potential target for the treatment of tendon injuries and diseases.

Inhibition of p38 mitogen-activated protein kinase signaling reduces fibrosis and lipid accumulation after rotator cuff repair.

BACKGROUND: The repair of rotator cuff tears is often complicated by fatty degeneration, which is the combination of lipid accumulation, fibrosis, inflammation, and muscle weakness. A signaling molecule that plays a central role in these processes is p38 mitogen-activated protein kinase (MAPK). The purpose of this study was to evaluate the ability of a small molecule inhibitor of p38 MAPK, SB203580, to reduce fatty degeneration in a preclinical model of rotator cuff injury and repair. MATERIALS AND METHODS: Adult rats underwent a bilateral supraspinatus tenotomy that was repaired 30 days later. Rats were treated with SB203580 or vehicle every 2 days, with injections beginning 3 days before surgery and continuing until 7 days after surgery. Two weeks after surgical repair, muscles were analyzed using histology, lipid profiling, gene expression, and permeabilized muscle fiber contractility. RESULTS: Inhibition of p38 MAPK resulted in a nearly 49% reduction in fat accumulation and a 29% reduction in collagen content, along with changes in corresponding genes regulating adipogenesis and matrix accumulation. There was also a marked 40% to 80% decrease in the expression of several proinflammatory genes, including IL1B, IL6, and COX2, and a 360% increase in the anti-inflammatory gene IL10. No differences were observed for muscle fiber force production. CONCLUSION: Inhibition of p38 MAPK was found to result in a significant decrease in intramuscular lipid accumulation and fibrosis that is usually seen in the degenerative cascade of rotator cuff tears, without having negative effects on the contractile properties of the rotator cuff muscle tissue.

Mitochondrial respiration atlas reveals differential changes in mitochondrial function across sex and age.

Organ function declines with age, and large-scale transcriptomic analyses have highlighted differential aging trajectories across tissues. The mechanisms underlying shared and organ-selective functional changes across the lifespan, however, still remains poorly understood. Given the central role of mitochondria in powering cellular processes needed to maintain tissue health, we therefore undertook a systematic assessment of respiratory activity across 33 different tissues in young (2.5 months) and old (20 months) mice of both sexes. Our high-resolution mitochondrial respiration atlas reveals: 1) within any group of mice, mitochondrial activity varies widely across tissues, with the highest values consistently seen in heart, brown fat, and kidney; 2) biological sex is a significant but minor contributor to mitochondrial respiration, and its contributions are tissue-specific, with major differences seen in the pancreas, stomach, and white adipose tissue; 3) age is a dominant factor affecting mitochondrial activity, especially across different fat depots and skeletal muscle groups, and most brain regions; 4) age-effects can be sex- and tissue-specific, with some of the largest effects seen in pancreas, heart, adipose tissue, and skeletal muscle; and 5) while aging alters the functional trajectories of mitochondria in a majority of tissues, some are remarkably resilient to age-induced changes. Altogether, our data provide the most comprehensive compendium of mitochondrial respiration and illuminate functional signatures of aging across diverse tissues and organ systems.

Tmem263 deletion disrupts the GH/IGF-1 axis and causes dwarfism and impairs skeletal acquisition.

Genome-wide association studies (GWAS) have identified a large number of candidate genes believed to affect longitudinal bone growth and bone mass. One of these candidate genes, TMEM263, encodes a poorly characterized plasma membrane protein. Single nucleotide polymorphisms in TMEM263 are associated with bone mineral density in humans and mutations are associated with dwarfism in chicken and severe skeletal dysplasia in at least one human fetus. Whether this genotype-phenotype relationship is causal, however, remains unclear. Here, we determine whether and how TMEM263 is required for postnatal growth. Deletion of the Tmem263 gene in mice causes severe postnatal growth failure, proportional dwarfism, and impaired skeletal acquisition. Mice lacking Tmem263 show no differences in body weight within the first 2 weeks of postnatal life. However, by P21 there is a dramatic growth deficit due to a disrupted growth hormone (GH)/insulin-like growth factor 1 (IGF-1) axis, which is critical for longitudinal bone growth. Tmem263-null mice have low circulating IGF-1 levels and pronounced reductions in bone mass and growth plate length. The low serum IGF-1 in Tmem263-null mice is associated with reduced hepatic GH receptor (GHR) expression and GH-induced JAK2/STAT5 signaling. A deficit in GH signaling dramatically alters GH-regulated genes and feminizes the liver transcriptome of Tmem263-null male mice, with their expression profile resembling wild-type female, hypophysectomized male, and Stat5b-null male mice. Collectively, our data validates the causal role for Tmem263 in regulating postnatal growth and raises the possibility that rare mutations or variants of TMEM263 may potentially cause GH insensitivity and impair linear growth.