Clostridioides difficile is a significant public health threat, and diagnosis of this infection is challenging due to a lack of sensitivity in current diagnostic testing. In this issue of the JCI, Robinson et al. use a logistic regression model based on the fecal metabolome that is able to distinguish between patients with non–C. difficile diarrhea and C. difficile infection, and to some degree, patients who are asymptomatically colonized with C. difficile. The authors construct a metabolic definition of human C. difficile infection, which could improve diagnostic accuracy and aid in the development of targeted therapeutics against this pathogen.
Casey M. Theriot, Joshua R. Fletcher
Developing effective treatments for obesity and related metabolic disease remains a challenge. One logical strategy targets the appetite-regulating actions of gut hormones such as incretins. One of these incretins, glucose-dependent insulinotropic polypeptide (GIP), has garnered much attention as a potential target: however, whether it is beneficial to boost or block the action of GIP to promote weight loss remains an unresolved question. In this issue of the JCI, Kaneko and colleagues show that antagonizing GIP signaling in the CNS enhances the weight-reducing effects of leptin in rodents with diet-induced obesity. The authors posit that an increase in circulating intestinally derived GIP, as a consequence of overnutrition, acts in the brain to impair hypothalamic leptin action, resulting in increased food intake and body weight gain. This research advances the idea that multiple GIP signaling pathways and mechanisms exist in the obese state and offers intriguing new insights into the antiobesogenic consequences of antagonizing brain GIP action.
Jessica T.Y. Yue, Tony K.T. Lam
Patients with Parkinson’s disease (PD) show selective degeneration of dopaminergic neurons in the substantia nigra and cholinergic neurons in the dorsal motor nucleus (DMnX), but the drivers of this specific susceptibility are unknown. In this issue of the JCI, Musgrove et al. report on their use of an impressive array of in vivo and ex vivo tools for interrogating DMnX neurons and demonstrate that this population exhibits enhanced sensitivity to oxidative stress. Remarkably, this sensitivity was amplified by the overexpression of α-Synuclein (α-Syn), a pathological protein in PD. They further show that oxidative stress augments cell-cell transfer of α-Syn, which may be an important mechanism underlying the development and progression of PD.
Kelvin C. Luk
Type 1 diabetes (T1D) results from autoimmune destruction of insulin-producing β cells in islets of Langerhans. Many genetic and immunological insights into autoimmune disease pathogenesis were initially uncovered in the context of T1D and facilitated by preclinical studies using the nonobese diabetic (NOD) mouse model. Recently, the study of T1D has led to the discovery of fatty acid esters of hydroxyl fatty acids (FAHFAs), which are naturally occurring hybrid peptides that modulate inflammation and diabetes pathogenesis, and a hybrid lymphocyte that expresses both B and T cell receptors. Palmitic acid esters of hydroxy stearic acids (PAHSAs) are the most extensively studied FAHFA. In this issue of the JCI, Syed et al. have shown that PAHSAs both attenuate autoimmune responses and promote β cell survival in NOD mice. Given the lack of effective T1D therapies and the paucity of known side effects of PAHSAs, this lipid may have therapeutic potential for individuals at risk for or newly diagnosed with T1D.
Abdel Rahim A. Hamad, Mohanraj Sadasivam, Hamid Rabb
Pancreatic ductal adenocarcinoma is projected to become the second leading cause of cancer-related death and is largely resistant to immunotherapies. The tumor microenvironment, largely composed of heterogeneous myeloid cells, creates a physical, metabolic, and immunosuppressive barrier that prevents T cells from infiltrating cancer beds. In this issue of the JCI, Markosyan and colleagues have reported a tumor-intrinsic mechanism that excludes T cells from the vicinity of tumor cells. They showed that a receptor tyrosine kinase, ephrin-A receptor 2 (EPHA2), regulates prostaglandin endoperoxide synthase 2 (PTGS2) (encodes COX-2) expression in a TGF-β signaling–dependent manner. Genetic ablation of Epha2 or Ptgs2 in preclinical models or pharmacological inhibition of COX-2 elicited the transformation of this immunosuppressive microenvironment into a T cell–permissive milieu. Consequent T cell relocation rendered this immunoresistant malignancy responsive to combinations of checkpoint blockers and CD40 agonists. Because the association between T cell infiltration and the EPHA2/TGF-β/COX-2 axis is supported by independent clinical data, these results provide a rationale for ensuing clinical trials aimed at incorporating pancreatic cancer into the range of immunotherapy-responsive tumors.
Jose R. Conejo-Garcia
The oxygen-sensing prolyl hydroxylase domain (PHD) enzymes are key to maintaining tissue homeostasis during hypoxia via their regulation of the expression and activity of HIF, the master transcription factor for the hypoxic response. In this issue of the JCI, Yamamoto, Hester, and colleagues show that temporal and reversible inhibition of PHD2 in vivo leads to systemic autoimmune disorder. The work demonstrates that a reduction of PHD2 leads to impairment of immunosuppressive Treg cell function via a HIF2α-dependent mechanism, without altering Foxp3 expression. This study indicates that a PHD2/HIF2α axis is critical for maintaining proper Treg function.
Weiping Zou, Yatrik M. Shah
Organ transplantation is now a preferred treatment for end-stage organ failure. Among the challenges for ensuring excellent clinical outcomes for transplant recipients is good initial allograft function at the time of organ implantation. This is determined in part by the functional status of the donor and donor organ, functional status of the recipient, and conduct of the operative procedure. Despite optimization of these variables, organ transplantation is still often plagued by substantial initial dysfunction, variably referred to as slow or delayed graft function, or in the most extreme cases, primary graft nonfunction necessitating urgent regrafting. In this issue of the JCI, Nakamura, Kageyama, Ito, Hirao, and colleagues investigate a potential role for the recipient’s microbiome in determining graft function after liver transplantation and demonstrate the benefits of antibiotic pretreatment in both a mouse model and in human patients.
Jonathan S. Bromberg, Joseph R. Scalea, Emmanuel F. Mongodin
Neurologic involvement of HIV remains an important concern for patients, physicians, and investigators. Catastrophic decline is rarely seen in patients on combination antiretroviral therapy (cART); however, neurological decline remains a critical clinical challenge. In this issue of the JCI, Spudich and associates investigated the status of HIV in the cerebral spinal fluid (CSF) and revealed ongoing presence of HIV in the nervous system. Surprisingly, even in the face of optimal treatment, including suppressed HIV RNA, almost half of the patients investigated showed cell-associated HIV (CA-HIV) DNA in the CSF. Spudich et al. find that persistence of HIV in CSF cells is associated with lower performance on neurocognitive testing. These findings emphasize the need to consider a viral-associated mechanism as playing a significant and potentially ongoing role in HIV-associated neurocognitive disorder (HAND).
David B. Clifford
The discovery of insulin almost 100 years ago has resulted in a remarkable increase in lifespan and quality of life for patients with type 1 diabetes. The Joslin Medalist Study has allowed researchers to access and study patients (Medalists) with type 1 diabetes who have been insulin dependent for 50 years or more. In this issue of the JCI, Yu et al. evaluated HLA variants, autoantibody status, β cell function, C-peptide release, and monogenetic diabetes genes in a cohort of Medalists. Postmortem analysis of pancreata from Medalists revealed the presence of insulin-positive β cells in these patients. Moreover, some patients were still able to respond to metabolic stimuli despite long-term insulin dependence. Overall, the Medalist cohort was highly heterogenous, and genetic testing suggested that several patients would fall into categories other than type 1 diabetes on the basis of REVEL (rare exome variant ensemble learner) classification and may be able to transfer to other therapy options.
Fabrizio Barbetti, Simeon I. Taylor
T follicular helper (Tfh) cells in germinal centers of secondary lymphoid organs are pivotal for B and T cell interactions required for induction of humoral immunity. It has long been debated whether Tfh cells exit from lymph nodes into the blood as circulating Tfh cells. In this issue of the JCI, Vella et al. have taken the bull by the horns and applied considerable technical muscle to answer this question. By analyzing phenotype, transcriptome, epigenetic profile, and T cell receptor clonotype, the authors provide evidence that a subset of cTfh cells do indeed originate in lymph nodes and traffic into the blood via the thoracic duct.
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