Review
Abstract
Endometriosis is an estrogen-dependent chronic inflammatory syndrome characterized by viable endometrial tissue outside the uterine cavity and associated with pain and infertility. Endometriosis, as tissue or a pathological process, is dynamic in that its establishment and progression require repeated episodes of retrograde travel of shed endometrial tissue, which implants in the lower abdominal cavity following ovulatory cycles and survives. Estrogen-rich follicular fluid released onto peritoneal surfaces during ovulation may also support endometriotic implants. DNA evidence indicates that endometriosis originates from eutopic endometrial tissue, which may reach the abdominal cavity in a retrograde manner primarily via the uterine tubes. Unlike uterine bleeding associated with non-ovulatory circumstances, retrograde menstruation following an ovulation maximizes shedding of epithelial cells localized to deep invaginations of the basalis portion of the endometrium, which likely carry somatic cancer-driver mutations such as KRAS. The attached endometrial stromal cells are mostly mutation free but display epigenetic defects including overexpression of aromatase and estrogen receptor-β and downregulation of progesterone receptor, causing estrogen excess and progesterone resistance. These tissue clones may form implants in involuting ovarian corpus luteum cysts and peritoneal surfaces and induce tissue remodeling and fibrosis, manifested as deep-infiltrating endometriosis. The first-line treatment for chronic pelvic pain associated with endometriosis is suppression of ovulation, with the goal of relieving pain. Infertility is often managed using in vitro fertilization, which improves the embryo quality and alters endometrial development.
Authors
Serdar E. Bulun
Abstract
Cancer care is being transformed by therapies leveraging T lymphocytes to attack tumor cells. In parallel, recent basic discoveries have converged into a framework of lymphocyte-dependent immunity as a regenerative process that is sometimes outstripped by high-level engagement. In a stem cell–like fashion, selected T cells must balance mutually opposing demands of differentiation and self-renewal. Activating versus inhibitory signals to T cells instruct opposing cell metabolism, linked to alternative cell fates that arise in sibling cells through lopsided information transfer. Emerging studies indicate that durable immunotherapy response may be limited by the abundance of self-renewing T cells. Leveraging of basic discoveries of regenerative signaling to bolster sustained, stem-like output of freshly differentiated T cells is offering new strategies to overcome cancer immunotherapy resistance. Lymphocyte regeneration may also sustain harmful autoimmune attack. Undercutting the self-renewal of pathogenic clones may thus emerge as a therapeutic strategy for autoimmune diseases.
Authors
Steven L. Reiner
Abstract
Metabolic dysfunction–associated steatotic liver disease (MASLD) is the most common pediatric liver disease, affecting approximately 10% of children. Its prevalence is rising at an alarming rate, with cases increasingly identified even in early childhood. While MASLD shares key features across the lifespan, its earlier onset reflects developmental vulnerabilities and unique mechanistic drivers. Perinatal influences, including maternal obesity, gestational diabetes, and early-life nutritional exposures, play a central role by disrupting metabolic programming, driving mitochondrial dysfunction, and inducing epigenetic modifications. These early stressors interact with genetic predispositions, such as PNPLA3 and TM6SF2 variants, to amplify susceptibility and shape disease severity. Pediatric MASLD also exhibits distinct histological features, particularly predominant periportal (zone 1) steatosis, inflammation, and fibrosis, which contrast with the centrilobular or pericentral (zone 3) patterns often seen in adults. These findings provide insight into spatial heterogeneity, developmental pathophysiology, and unique disease progression trajectories in children. Addressing MASLD in children requires pediatric-specific approaches to diagnosis, risk stratification, and intervention. By integrating epidemiological trends, mechanistic insights, and translational advances, this Review highlights opportunities for targeted therapies and prevention strategies aimed at mitigating early-life drivers of MASLD, reducing disease burden, and improving long-term outcomes.
Authors
Jeffrey B. Schwimmer, Sudha B. Biddinger, Samar H. Ibrahim
Abstract
Metabolic dysfunction–associated steatohepatitis (MASH), the progressive inflammatory form of MASLD, is now a leading cause of chronic liver disease worldwide. Driven by obesity and type 2 diabetes, MASH significantly increases the risk of cirrhosis, hepatocellular carcinoma, and liver failure. While public health interventions remain essential, therapeutic strategies targeting metabolic dysfunction, inflammation, and fibrosis are urgently needed. This Review focuses on pharmacological treatments in advanced development, including incretin-based therapies (GLP-1, dual, and triple agonists), metabolic modulators (PPAR, FGF21, and THR-β agonists), and novel agents such as fatty acid synthase inhibitors. Current regulatory approval is based on histological end points, with increasing interest in noninvasive biomarkers and personalized treatment approaches. Recent trials with agents such as semaglutide, tirzepatide, survodutide, lanifibranor, pegozafermin, and resmetirom demonstrate substantial promise in resolving MASH and improving fibrosis, but unresolved issues remain regarding treatment duration, response heterogeneity, and long-term adherence. Genetic variants (e.g., PNPLA3 polymorphisms) and emerging molecular biomarkers may enhance stratification, while artificial intelligence is beginning to shape trial design and drug development. As the field moves toward combination therapies and precision medicine, the definition of therapeutic success will likely evolve to reflect both histological improvement and patient-reported outcomes. This Review provides a timely synthesis of the landscape, challenges, and future directions in MASH therapeutics.
Authors
Philip N. Newsome, Rohit Loomba
Abstract
Animal experiments have long been a cornerstone of advancements in biomedical research, particularly in developing novel therapeutic strategies for inflammatory and autoimmune diseases. However, these historically important approaches are now facing growing scrutiny for ethical reasons, concerns about translational limitations to human biology, and the rising availability of animal-free research methods. This shift raises a critical question: How relevant and effective are animal models for driving future advancements in today’s research landscape? This Review aims to explore this question within the field of biomedical research on the complement system, critically evaluating the contribution of animal models to the recent advancements and clinical successes of complement-targeted therapies. Specifically, we assess areas where animal studies have been indispensable for elucidating disease mechanisms and conducting preclinical evaluations, alongside instances where findings from animal models failed to translate successfully to human trials. Furthermore, we discuss similarities and differences in the complement system between animals and humans and explore innovations in animal research designed to improve translatability to human biology. By assessing the contributions of animal studies to complement therapeutics, this Review aims to provide insights into animal models’ strengths, limitations, and evolving role in complement research.
Authors
Felix Poppelaars, V. Michael Holers, Joshua M. Thurman
Abstract
The complement system is an important component of the innate immune system involved in host defense and maintaining homeostasis. While the liver is the main source of complement proteins in the bloodstream, recent research has shown that various tissues, including the kidneys, can produce complement components locally in response to both acute and chronic inflammation. This Review highlights evidence from animal models of glomerular and tubulointerstitial kidney disease showing increased expression of intracellular complement in the kidneys. Studies using knockout mice for complement and complement receptors, along with complement inhibitors, have demonstrated that reduced complement activation in animal models of kidney fibrosis led to reduced inflammation and fibrosis, thereby supporting the pathogenic role of complement activation. Data from single-cell RNA-sequencing, spatial transcriptomics, and proteomics studies further demonstrate that alterations in local complement levels contribute to the fibrotic microenvironment observed in these models. Additionally, kidney biopsy results from patients with acute kidney injury and chronic kidney disease (CKD) indicate an increased expression of intracellular complement components as disease progresses. Developing drugs aimed at diminishing the expression and activation of local complement in glomerular and tubulointerstitial kidney disease could provide a novel approach to managing CKD.
Authors
Didier Portilla, Vikram Sabapathy, Daniel Chauss
Abstract
The complement system is a highly conserved and essential immune component with pivotal roles in innate and adaptive immunity. It is increasingly recognized that the complement system has a profound impact on disease. Current complement-targeting therapeutics for clinical use almost exclusively target the complement system in circulation. However, recent discoveries have demonstrated that complement is not only liver derived and plasma operative, but also synthesized and activated inside many cells locally within tissues, performing noncanonical, cell-autonomous intracellular functions, collectively referred to as the complosome. These intracellular complement pathways are distinct from the classical plasma-based system and critical for regulating fundamental cellular processes, including metabolism, gene transcription, autophagy, and the activation and resolution of inflammation. This Review explores the emerging roles of the complosome and current knowledge regarding its relation to human diseases, highlighting evidence across organ systems and disease states, including the kidneys, digestive tract, lungs, heart, CNS, musculoskeletal system, skin, and cancer. We also review current scientific approaches for detecting and functionally investigating the complosome, addressing challenges such as technological limitations and the need for advanced experimental models to delineate its tissue-specific roles. Finally, we discuss central unanswered questions critical for developing innovative therapeutic strategies targeting intracellular complement pathways. These strategies hold potential to modulate disease-specific mechanisms while preserving systemic complement activity.
Authors
Tilo Freiwald, Behdad Afzali
Abstract
Acute pain management has historically been dominated by opioids, whose efficacy is overshadowed by the risks of addiction, tolerance, and dependence, culminating in the global opioid crisis. To transcend this issue, we must innovate beyond opioid-based μ receptor treatments, identifying nonopioid analgesics with high efficacy and minimal adverse effects. This Review navigates the multifaceted landscape of inflammatory, neuropathic, and nociplastic pain, emphasizing mechanism-based analgesic targets tailored to specific pain conditions. We delve into the challenges and breakthroughs in clinical trials targeting ion channels, GPCRs, and other molecular targets. We also highlight the intricate crosstalk between different physiological systems and the need for multimodal interventions with distinct pharmacodynamics to manage acute and chronic pain, respectively. Furthermore, we explore emerging strategies, including gene therapy, stem cell therapy, cell type–specific neuromodulation, and AI-driven techniques for objective, unbiased pain assessment and research. These innovative approaches are poised to revolutionize pain management, paving the way for the discovery of safer and more effective analgesics.
Authors
Xiangsunze Zeng, Rasheen Powell, Clifford J. Woolf
Abstract
Chronic pain affects more than 50 million Americans, with women disproportionately affected by severe pain, pain interference, and overall disability. The development of chronic pain is multifactorial and often begins with an incident of acute pain associated with an injury or a surgical procedure that transitions to persistent pain lasting for months or years. Despite this, there are limited clinical studies investigating sex differences in predictors and biomarkers for the transition to chronic pain. Several preclinical animal models have been developed to gain a better understanding of the mechanisms for the transition to chronic pain, and several sex-specific mechanisms have been identified across multiple systems. These preclinical models generally involve a multiple-insult approach, in which a priming insult enhances sensitivity to a subsequent induction stimulus. There is emerging evidence from preclinical research for several male-specific and female-specific mechanisms, as well as several studies showing shared mechanisms. Here, we review the clinical and preclinical literature covering sex differences in the periphery and immune system, the central nervous system, and the endocrine system related to the transition to chronic pain. We further highlight gaps in the literature and provide recommendations for future research to understand sex-specific differences in the transition to chronic pain.
Authors
Angela F. Smith, Ashley N. Plumb, Giovanni Berardi, Kathleen A. Sluka
Abstract
Bacterial vaginosis (BV) is a polymicrobial condition of the vaginal microbiota associated with a variety of sexually transmitted infections, infections of maternal and fetal tissues during pregnancy, and even some infections outside of the reproductive tract, including the urinary tract and mouth. BV has also been associated with conditions in which the body generates prominent inflammatory reactions to microbes, including infections of the cervix and other upper genital tract tissues. For reasons still not understood, BV is a highly recurrent and often difficult-to-treat condition, complicating attempts to prevent these associated infections. An additional layer of complexity arises from the increasing awareness that the presence of BV-associated bacteria in the vagina is not always symptomatic or associated with adverse outcomes. In this concise Review, we summarize and synthesize three groups of factors grounded in the literature that may be fueling the associations between BV and infection: (a) aspects of society and culture; (b) pathogens, virulence factors, and processes of microbial antagonism and synergy; and (c) host factors, such as genetics and immunity. Our goal is to understand what contexts and combinations of microbial, host, and social factors conspire to make BV virulent in some individuals but not others. Disrupting these patterns more systematically may achieve healthier outcomes.
Authors
Nicole M. Gilbert, Luis A. Ramirez Hernandez, Daniela Berman, Sydney Morrill, Pascal Gagneux, Amanda L. Lewis
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