Understanding the glioblastoma tumor microenvironment: leveraging the extracellular matrix to increase immunotherapy efficacy.

Glioblastoma (GBM) accounts for approximately half of all malignant brain tumors, and it remains lethal with a five-year survival of less than 10%. Despite the immense advancements in the field, it has managed to evade even the most promising therapeutics: immunotherapies. The main reason is the highly spatiotemporally heterogeneous and immunosuppressive GBM tumor microenvironment (TME). Accounting for this complex interplay of TME-driven immunosuppression is key to developing effective therapeutics. This review will explore the immunomodulatory role of the extracellular matrix (ECM) by establishing its contribution to the TME as a key mediator of immune responses in GBM. This relationship will help us elucidate therapeutic targets that can be leveraged to develop and deliver more effective immunotherapies.

Myeloid cell-derived creatine in the hypoxic niche promotes glioblastoma growth.

Glioblastoma (GBM) is a malignancy dominated by the infiltration of tumor-associated myeloid cells (TAMCs). Examination of TAMC metabolic phenotypes in mouse models and patients with GBM identified the de novo creatine metabolic pathway as a hallmark of TAMCs. Multi-omics analyses revealed that TAMCs surround the hypoxic peri-necrotic regions of GBM and express the creatine metabolic enzyme glycine amidinotransferase (GATM). Conversely, GBM cells located within these same regions are uniquely specific in expressing the creatine transporter (SLC6A8). We hypothesized that TAMCs provide creatine to tumors, promoting GBM progression. Isotopic tracing demonstrated that TAMC-secreted creatine is taken up by tumor cells. Creatine supplementation protected tumors from hypoxia-induced stress, which was abrogated with genetic ablation or pharmacologic inhibition of SLC6A8. Lastly, inhibition of creatine transport using the clinically relevant compound, RGX-202-01, blunted tumor growth and enhanced radiation therapy in vivo. This work highlights that myeloid-to-tumor transfer of creatine promotes tumor growth in the hypoxic niche.

Feasibility Randomised Control Trial of OptiMal: A Self-Management Intervention for Cancer Survivors.

PURPOSE: Cancer survivors can experience symptoms such as fatigue, pain and distress that persist for many months following treatment. These enduring symptoms often impact on participation in self-care activities, returning to school and/or work, and leisure and social activities. Self-management support is increasingly recognised as a core aspect of cancer survivorship care to reduce the impact of persistent symptoms. The purpose of this study was to examine the feasibility and potential effectiveness of a group-based self-management intervention, OptiMal, to improve the physical and psychological health of cancer survivors. OptiMal is a six-week intervention comprising weekly sessions on fatigue, stress and physical activity, diet and effective communication strategies. METHODS: A feasibility randomised control trial was undertaken. Individuals up to two years after cancer treatment were randomised to OptiMal or usual care. Feasibility was examined through recruitment and retention metrics. Potential effectiveness was tested through patient-reported outcomes collected at baseline and three months post-intervention. Descriptive and inferential statistics were used to analyse study data. RESULTS: Recruitment for this study was 32.5% (80/246 eligible individuals) with 77.5% retention at three-month follow-up (82.5% for intervention group and 72.5% for control group). Of those who attended the intervention, 19 (73%) attended all OptiMal sessions, indicating high adherence to the intervention. The majority of participants had breast cancer and were between 12 and 24 months post-treatment. The intervention group (n = 29) had statistically significant greater improvements in anxiety (p = 0.04) and health-related quality of life (health index score: p = 0.023, visual analogue score: p = 0.035) at three months post-intervention than the control group. CONCLUSIONS: Recruitment and retention in this study was similar to other cancer trials and the high adherence rate indicates that OptiMal is an acceptable self-management intervention for cancer survivors and warrants further investigation. OptiMal is intended to address symptoms reported across different cancer types. However, a limitation of this study was that the majority of participants had breast cancer, and therefore, generalisability of findings cannot be assumed for other cancer types. Future studies of OptiMal therefore need to use different strategies to recruit survivors of other cancer types.

Efferocytosis of viable versus heat-inactivated MSC induces human monocytes to distinct immunosuppressive phenotypes.

BACKGROUND: Immunomodulation by mesenchymal stromal cells (MSCs) can occur through trophic factor mechanisms, however, intravenously infused MSCs are rapidly cleared from the body yet a potent immunotherapeutic response is still observed. Recent work suggests that monocytes contribute to the clearance of MSCs via efferocytosis, the body's natural mechanism for clearing dead and dying cells in a non-inflammatory manner. This begs the questions of how variations in MSC quality affect monocyte phenotype and if viable MSCs are even needed to elicit an immunosuppressive response. METHODS: Herein, we sought to dissect MSC's trophic mechanism from their efferocytic mechanisms and determine if the viability of MSCs prior to efferocytosis influences the resultant phenotype of monocytes. We cultured viable or heat-inactivated human umbilical cord MSCs with human peripheral blood mononuclear cells for 24 h and observed changes in monocyte surface marker expression and secretion profile. To isolate the effect of efferocytosis from MSC trophic factors, we used cell separation techniques to remove non-efferocytosed MSCs before challenging monocytes to suppress T-cells or respond to inflammatory stimuli. For all experiments, viable and heat-inactivated efferocytic-licensing of monocytes were compared to non-efferocytic-licensing control. RESULTS: We found that monocytes efferocytose viable and heat-inactivated MSCs equally, but only viable MSC-licensed monocytes suppress activated T-cells and suppression occurred even after depletion of residual MSCs. This provides direct evidence that monocytes that efferocytose viable MSCs are immunosuppressive. Further characterization of monocytes after efferocytosis showed that uptake of viable-but not heat inactivated-MSC resulted in monocytes secreting IL-10 and producing kynurenine. When monocytes were challenged with LPS, IL-2, and IFN-γ to simulate sepsis, monocytes that had efferocytosed viable MSC had higher levels of IDO while monocytes that efferocytosed heat inactivated-MSCs produced the lowest levels of TNF-α. CONCLUSION: Collectively, these studies show that the quality of MSCs efferocytosed by monocytes polarize monocytes toward distinctive immunosuppressive phenotypes and highlights the need to tailor MSC therapies for specific indications.

The CXCL16-CXCR6 axis in glioblastoma modulates T-cell activity in a spatiotemporal context.

Introduction: Glioblastoma multiforme (GBM) pathobiology is characterized by its significant induction of immunosuppression within the tumor microenvironment, predominantly mediated by immunosuppressive tumor-associated myeloid cells (TAMCs). Myeloid cells play a pivotal role in shaping the GBM microenvironment and influencing immune responses, with direct interactions with effector immune cells critically impacting these processes. Methods: Our study investigates the role of the CXCR6/CXCL16 axis in T-cell myeloid interactions within GBM tissues. We examined the surface expression of CXCL16, revealing its limitation to TAMCs, while microglia release CXCL16 as a cytokine. The study explores how these distinct expression patterns affect T-cell engagement, focusing on the consequences for T-cell function within the tumor environment. Additionally, we assessed the significance of CXCR6 expression in T-cell activation and the initial migration to tumor tissues. Results: Our data demonstrates that CXCL16 surface expression on TAMCs results in predominant T-cell engagement with these cells, leading to impaired T-cell function within the tumor environment. Conversely, our findings highlight the essential role of CXCR6 expression in facilitating T-cell activation and initial migration to tumor tissues. The CXCL16-CXCR6 axis exhibits dualistic characteristics, facilitating the early stages of the T-cell immune response and promoting T-cell infiltration into tumors. However, once inside the tumor, this axis contributes to immunosuppression. Discussion: The dual nature of the CXCL16-CXCR6 axis underscores its potential as a therapeutic target in GBM. However, our results emphasize the importance of carefully considering the timing and context of intervention. While targeting this axis holds promise in combating GBM, the complex interplay between TAMCs, microglia, and T cells suggests that intervention strategies need to be tailored to optimize the balance between promoting antitumor immunity and preventing immunosuppression within the dynamic tumor microenvironment.

Translating MSC Therapy in the Age of Obesity.

Mesenchymal stromal cell (MSC) therapy has seen increased attention as a possible option to treat a number of inflammatory conditions including COVID-19 acute respiratory distress syndrome (ARDS). As rates of obesity and metabolic disease continue to rise worldwide, increasing proportions of patients treated with MSC therapy will be living with obesity. The obese environment poses critical challenges for immunomodulatory therapies that should be accounted for during development and testing of MSCs. In this review, we look to cancer immunotherapy as a model for the challenges MSCs may face in obese environments. We then outline current evidence that obesity alters MSC immunomodulatory function, drastically modifies the host immune system, and therefore reshapes interactions between MSCs and immune cells. Finally, we argue that obese environments may alter essential features of allogeneic MSCs and offer potential strategies for licensing of MSCs to enhance their efficacy in the obese microenvironment. Our aim is to combine insights from basic research in MSC biology and clinical trials to inform new strategies to ensure MSC therapy is effective for a broad range of patients.

Systemic Mesenchymal Stem Cell Treatment Mitigates Structural and Functional Retinal Ganglion Cell Degeneration in a Mouse Model of Multiple Sclerosis.

Purpose: The purpose of this study was to determine mesenchymal stem cell (MSC) therapy efficacy on rescuing the visual system in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS) and to provide new mechanistic insights. Methods: EAE was induced in female C57BL6 mice by immunization with myelin oligodendrocyte glycoprotein (MOG)35-55, complete Freund's adjuvant, and pertussis toxin. The findings were compared to sham-immunized mice. Half of the EAE mice received intraperitoneally delivered stem cells (EAE + MSC). Clinical progression was monitored according to a five-point EAE scoring scheme. Pattern electroretinogram (PERG) and retinal nerve fiber layer (RNFL) thickness were measured 32 days after induction. Retinas were harvested to determine retinal ganglion cell (RGC) density and prepared for RNA-sequencing. Results: EAE animals that received MSC treatment seven days after EAE induction showed significantly lower motor-sensory impairment, improvement in the PERG amplitude, and preserved RNFL. Analysis of RNA-sequencing data demonstrated statistically significant differences in gene expression in the retina of MSC-treated EAE mice. Differentially expressed genes were enriched for pathways involved in endoplasmic reticulum stress, endothelial cell differentiation, HIF-1 signaling, and cholesterol transport in the MSC-treated EAE group. Conclusions: Systemic MSC treatment positively affects RGC function and survival in EAE mice. Better cholesterol handling by increased expression of Abca1, the cholesterol efflux regulatory protein, paired with the resolution of HIF-1 signaling activation might explain the improvements seen in PERG of EAE animals after MSC treatment. Translational Relevance: Using MSC therapy in a mouse model of MS, we discovered previously unappreciated biochemical pathways associated with RGC neuroprotection, which have the potential to be pharmacologically targeted as a new treatment regimen.

Dose and duration of interferon γ pre-licensing interact with donor characteristics to influence the expression and function of indoleamine-2,3-dioxygenase in mesenchymal stromal cells.

Human mesenchymal stromal cells (MSCs) are a leading cell therapy candidate for the treatment of immune and inflammatory diseases due to their potent regulation of immune cells. MSC expression of indoleamine-2,3-dioxygenase (IDO) upon interferon γ (IFNγ) exposure has been proposed as both a sentinel marker and key mediator of MSC immunomodulatory potency. Rather than wait for in vivo exposure to cytokines, MSCs can be pre-licensed during manufacturing to enhance IDO expression. In this study, we systematically examine the relative role that the dose of IFNγ, the duration of pre-licensing and the donor of origin play in dictating MSC production of functional IDO. We find that across three human MSC donors, MSCs increase their expression of IDO in response to both increased dose of IFNγ and duration of pre-licensing. However, with extended pre-licensing, the expression of IDO no longer predicts MSCs ability to suppress activated peripheral blood mononuclear cells. In addition, pre-licensing dose and duration are revealed to be minor modifiers of MSCs inherent potency, and thus cannot be manipulated to boost poor donors to the levels of high-performing donors. Thus, the dose and duration of pre-licensing should be tailored to optimize performance of specific donors and an emphasis on donor selection is needed to realize significant benefits of pre-licensing.

Adipose TBX1 regulates ß-adrenergic sensitivity in subcutaneous adipose tissue and thermogenic capacity in vivo.

OBJECTIVE: T-box 1 (TBX1) has been identified as a genetic marker of beige adipose tissue. TBX1 is a mesodermal development transcription factor essential for tissue patterning and cell fate determination. However, whether it plays a role in the process of adipose beiging or how it functions in adipose tissue has not been reported. Here, we examined the function of TBX1 in adipose tissue as well as adipose-derived stem cells from mice and humans. METHODS: Adipose-specific TBX1 transgenic (TBX1 AdipoTG) and adipose-specific TBX1 knockout (TBX1 AdipoKO) mice were generated to explore the function of TBX1 in the process of adipose beiging, metabolism and energy homeostasis in vivo. In vitro, we utilized a siRNA mediated approach to determine the function of TBX1 during adipogenesis in mouse and human stem cells. RESULTS: Adipose-specific overexpression of TBX1 was not sufficient to fully induce beiging and prevent diet-induced obesity. However, adipose TBX1 expression was necessary to defend body temperature during cold through regulation of UCP1 and for maintaining ß3-adrenergic sensitivity and glucose homeostasis in vivo. Loss of adipose TBX1 expression enhanced basal lipolysis and reduced the size of subcutaneous iWAT adipocytes. Reduction of TBX1 expression via siRNA significantly impaired adipogenesis of mouse stromal vascular cells but significantly enhanced adipogenesis in human adipose derived stem cells. CONCLUSIONS: Adipose expression of TBX1 is necessary, but not sufficient, to defend body temperature during cold via proper UCP1 expression. Adipose TBX1 expression was also required for proper insulin signaling in subcutaneous adipose as well as for maintaining ß-adrenergic sensitivity, but overexpression of TBX1 was not sufficient to induce adipocyte beiging or to prevent diet-induced obesity. TBX1 expression is enriched in adipose stem cells in which it has contrasting effects on adipogenesis in mouse versus human cells. Collectively, these data demonstrate the importance of adipose TBX1 in the regulation of beige adipocyte function, energy homeostasis, and adipocyte development.

Aggregation of Human Mesenchymal Stromal Cells Eliminates Their Ability to Suppress Human T Cells.

Mesenchymal stromal cells (MSCs) are administered locally to treat sites of inflammation. Local delivery is known to cause MSCs to aggregate into "spheroids," which alters gene expression and phenotype. While adherent MSCs are highly efficient in their inhibition of T cells, whether or not this property is altered upon MSC aggregation has not been thoroughly determined. In this study, we discovered that aggregation of MSCs into spheroids causes them to lose their T cell-suppressive abilities. Interestingly, adding budesonide, a topical glucocorticoid steroid, alongside spheroids partially restored MSC suppression of T cell proliferation. Through a series of inhibition and add-back studies, we determined budesonide acts synergistically with spheroid MSC-produced PGE2 to suppress T cell proliferation through the PGE2 receptors EP2 and EP4. These findings highlight critical differences between adherent and spheroid MSC interactions with human immune cells that have significant translational consequences. In addition, we uncovered a mechanism through which spheroid MSC suppression of T cells can be partly restored. By understanding the phenotypic changes that occur upon MSC aggregation and the impact of MSC drug interactions, improved immunosuppressive MSC therapies for localized delivery can be designed.

Perspectives of Esophageal Cancer Survivors on Diagnosis, Treatment, and Recovery.

Esophageal cancer poses challenges to all domains of wellbeing. This qualitative study aimed to explore the experiences of esophageal cancer diagnosis, treatment, and recovery, with a view to informing the health education needs of this group. Eighteen persons who had undergone an esophagectomy participated in one of four audio-taped focus groups in a specialist hospital for cancer care. Transcriptions were analyzed thematically. Fear and uncertainty underpinned all stages of diagnosis, treatment, and recovery. Participants emphasized: (a) a lack of understanding over what to expect throughout treatment and recovery; (b) the demanding and traumatic period of adjustment required as a result of changes to their physical, psychological, and social functioning; and, (c) that support provided by family, friends, and acquaintances was variable and uninformed, often to the point of being counterproductive to physical and psychosocial recovery. Tailored education is needed to enable patients to prepare for each stage of their cancer journey. Equally, families and wider social networks should receive education that enables them to provide esophageal cancer survivors with appropriate support. Education should be provided at intervals that enable patients, survivors, and support networks to prepare for the physical, emotional, and social challenges experienced during diagnosis, treatment, and recovery.

The Popeye domain containing gene family encoding a family of cAMP-effector proteins with important functions in striated muscle and beyond.

The Popeye domain containing (POPDC) gene family encodes a novel class of membrane-bound cyclic AMP effector proteins. POPDC proteins are abundantly expressed in cardiac and skeletal muscle. Consistent with its predominant expression in striated muscle, Popdc1 and Popdc2 null mutants in mouse and zebrafish develop cardiac arrhythmia and muscular dystrophy. Likewise, mutations in POPDC genes in patients have been associated with cardiac arrhythmia and muscular dystrophy phenotypes. A membrane trafficking function has been identified in this context. POPDC proteins have also been linked to tumour formation. Here, POPDC1 plays a role as a tumour suppressor by limiting c-Myc and WNT signalling. Currently, a common functional link between POPDC's role in striated muscle and as a tumour suppressor is lacking. We also discuss several alternative working models to better understand POPDC protein function.

Nature vs. Nurture: Defining the Effects of Mesenchymal Stromal Cell Isolation and Culture Conditions on Resiliency to Palmitate Challenge.

As MSC products move from early development to clinical translation, culture conditions shift from xeno- to xeno-free systems. However, the impact of isolation and culture-expansion methods on the long-term resiliency of MSCs within challenging transplant environments is not fully understood. Recent work in our lab has shown that palmitate, a saturated fatty acid elevated in the serum of patients with obesity, causes MSCs to convert from an immunosuppressive to an immunostimulatory state at moderate to high physiological levels. This demonstrated that metabolically-diseased environments, like obesity, alter the immunomodulatory efficacy of healthy donor MSCs. In addition, it highlighted the need to test MSC efficacy not only in ideal conditions, but within challenging metabolic environments. To determine how the choice of xeno- vs. xeno-free media during isolation and expansion would affect future immunosuppressive function, umbilical cord explants from seven donors were subdivided and cultured within xeno- (fetal bovine serum, FBS) or xeno-free (human platelet lysate, PLT) medias, creating 14 distinct MSC preparations. After isolation and primary expansion, umbilical cord MSCs (ucMSC) were evaluated according to the ISCT minimal criteria for MSCs. Following baseline characterization, ucMSC were exposed to physiological doses of palmitate and analyzed for metabolic health, apoptotic induction, and immunomodulatory potency in co-cultures with stimulated human peripheral blood mononuclear cells. The paired experimental design (each ucMSC donor grown in two distinct culture environments) allowed us to delineate the contribution of inherent (nature) vs. environmentally-driven (nurture) donor characteristics to the phenotypic response of ucMSC during palmitate exposure. Culturing MSCs in PLT-media led to more consistent growth characteristics during the isolation and expansion for all donors, resulting in faster doubling times and higher cell yields compared to FBS. Upon palmitate challenge, PLT-ucMSCs showed a higher susceptibility to palmitate-induced metabolic disturbance, but less susceptibility to palmitate-induced apoptosis. Most striking however, was that the PLT-ucMSCs resisted the conversion to an immunostimulatory phenotype better than their FBS counterparts. Interestingly, examining MSC suppression of PBMC proliferation at physiologic doses of palmitate magnified the differences between donors, highlighting the utility of evaluating MSC products in stress-based assays that reflect the challenges MSCs may encounter post-transplantation.

IFN-γ and TNF-α Pre-licensing Protects Mesenchymal Stromal Cells from the Pro-inflammatory Effects of Palmitate.

The use of mesenchymal stromal cell (MSC) therapy for the treatment of type 2 diabetes (T2D) and T2D complications is promising; however, the investigation of MSC function in the setting of T2D has not been thoroughly explored. In our current study, we investigated the phenotype and function of MSCs in a simulated in vitro T2D environment. We show that palmitate, but not glucose, exposure impairs MSC metabolic activity with moderate increases in apoptosis, while drastically affecting proliferation and morphology. In co-culture with peripheral blood mononuclear cells (PBMCs), we found that MSCs not only lose their normal suppressive ability in high levels of palmitate, but actively support and enhance inflammation, resulting in elevated PBMC proliferation and pro-inflammatory cytokine release. The pro-inflammatory effect of MSCs in palmitate was partially reversed via palmitate removal and fully reversed through pre-licensing MSCs with interferon-gamma and tumor necrosis factor alpha. Thus, palmitate, a specific metabolic factor enriched within the T2D environment, is a potent modulator of MSC immunosuppressive function, which may in part explain the depressed potency observed in MSCs isolated from T2D patients. Importantly, we have also identified a robust and durable pre-licensing regimen that protects MSC immunosuppressive function in the setting of T2D.

Self-management interventions for cancer survivors: a systematic review.

PURPOSE: Many cancer survivors experience problems with persisting symptoms such as pain, fatigue, anxiety and depression post-treatment. Self-management interventions are recommended for cancer patients as they can help individuals identify and manage these continuing symptoms. This systematic review examines the type, content and impact of self-management interventions for cancer survivors on health outcomes such as activity participation, self-efficacy, quality of life and symptom management. METHODS: This was a systematic review of the English language scientific literature searched for randomised controlled trials (RCT), systematic reviews and meta-analyses of self-management programmes conducted with cancer survivors. Six databases were systematically searched. RESULTS: Initial searches yielded 2633 citations. Following screening and a risk of bias assessment, six studies were included in the final review. Heterogeneity of the interventions precluded meta-analysis. Three studies reported significant differences between groups in a number of areas including fatigue, physical functioning, distress and self-efficacy at their first follow-up assessment. These studies included two psychosocial interventions and one exercise and diet intervention. Not all findings were sustained across studies at follow-up assessment. CONCLUSION: It is not possible to draw definitive conclusions as to the impact the different types of self-management programme had on cancer survivors. The sustainability of the interventions reviewed was poor, suggesting that cancer survivors require interventions that can be applied into their daily activities.

A Low-Cost Technique for Intraoperative Imaging of Cell Delivery and Retention in a Model of Delayed Wound Healing.

Objective: Techniques to validate successful delivery of cell products are expensive, time-consuming, and require transport of the animal to imaging facilities, preventing their widespread use as documentation tools. The goal of this study was to determine if a low-cost portable microscope could provide sufficient performance to be used to document delivery of cell products and track retention over time. Approach: A Dino-Lite fluorescence microscope and an Odyssey CLx whole-animal scanner were compared on the basis of resolution, sensitivity, and linearity. The impact of different injection profiles on image quality was also compared and the system was used to track cells, injected freely or on scaffolds, in a model of diabetic wound healing. Results: Both systems were able to detect 50 fluorescently labeled cells and there was a linear relationship between the fluorescence signal and cell number in vitro. In vivo, both systems were found to be nonlinear, but highly correlated with one another. The Dino-Lite system was able to distinguish between depth of injection, diffuse injections, subcutaneous injections, and failed injections. Innovation: In contrast to traditional imaging systems, the technique presented here is affordable, rapid enough that it can be used to validate every injection, and can be brought to the animal, reducing handling and stress that may interfere with wound healing processes. Conclusion: Collectively, we found that the speed, affordability, and portability of handheld microscopes combined with their technical capabilities make them a valuable and accessible tool for routine validation, documentation, and tracking of cell products delivered to wounds.

Depletion of macrophages in CD11b diphtheria toxin receptor mice induces brain inflammation and enhances inflammatory signaling during traumatic brain injury.

Immune cells have important roles during disease and are known to contribute to secondary, inflammation-induced injury after traumatic brain injury. To delineate the functional role of macrophages during traumatic brain injury, we depleted macrophages using transgenic CD11b-DTR mice and subjected them to controlled cortical impact. We found that macrophage depletion had no effect on lesion size assessed by T2-weighted MRI scans 28 days after injury. Macrophage depletion resulted in a robust increase in proinflammatory gene expression in both the ipsilateral and contralateral hemispheres after controlled cortical impact. Interestingly, this sizeable increase in inflammation did not affect lesion development. We also showed that macrophage depletion resulted in increased proinflammatory gene expression in the brain and kidney in the absence of injury. These data demonstrate that depletion of macrophages in CD11b-DTR mice can significantly modulate the inflammatory response during brain injury without affecting lesion formation. These data also reveal a potentially confounding inflammatory effect in CD11b-DTR mice that must be considered when interpreting the effects of macrophage depletion in disease models.

Regulation of Insulin Receptor Trafficking by Bardet Biedl Syndrome Proteins.

Insulin and its receptor are critical for the regulation of metabolic functions, but the mechanisms underlying insulin receptor (IR) trafficking to the plasma membrane are not well understood. Here, we show that Bardet Biedl Syndrome (BBS) proteins are necessary for IR localization to the cell surface. We demonstrate that the IR interacts physically with BBS proteins, and reducing the expression of BBS proteins perturbs IR expression in the cell surface. We show the consequence of disrupting BBS proteins for whole body insulin action and glucose metabolism using mice lacking different BBS genes. These findings demonstrate the importance of BBS proteins in underlying IR cell surface expression. Our data identify defects in trafficking and localization of the IR as a novel mechanism accounting for the insulin resistance commonly associated with human BBS. This is supported by the reduced surface expression of the IR in fibroblasts derived from patients bearing the M390R mutation in the BBS1 gene.