Review coordinated by Life Science Editors Foundation Reviewed by: Dr. Angela Andersen, Life Science Editors Foundation Potential Conflicts of Interest: None

PUNCHLINE. This preprint identifies CCL2 as a central inflammatory driver of cachexia in autophagy-deficient mice, revealing a novel neuroinflammatory mechanism that suppresses appetite and leads to lethal wasting. In the absence of Atg7, systemic inflammation elevates CCL2, which targets and depletes hypothalamic neurons that promote feeding, specifically those expressing orexin and melanin-concentrating hormone (MCH). This neuronal loss triggers anorexia, metabolic failure, and death. Genetic deletion of Ccl2 or restoration of appetite via leptin deficiency fully rescues survival. However, anti-CCL2 antibodies fail to replicate this protection, highlighting the challenge of targeting cytokines in complex inflammatory states. The findings reframe cachexia as a disorder of brain-centered inflammation, with CCL2 as a key mediator.

BACKGROUND. Autophagy, the lysosomal degradation pathway essential for maintaining cellular homeostasis, is crucial during starvation and in the fed state. Systemic deletion of core autophagy genes like Atg5 or Atg7 in adult mice leads to rapid-onset weight loss, liver inflammation, and neurodegeneration—hallmarks of cachexia, a syndrome common in cancer, chronic kidney disease, and neurodegeneration. Interestingly, restoring autophagy in neurons alone can rescue neonatal lethality, suggesting that brain function is critical to systemic survival. This study addresses a fundamental question: how does autophagy protect against cachexia, and what are the mediators of its failure?

KEY QUESTION ADDRESSED. How does impaired autophagy in the adult organism lead to cachexia, and what is the role of brain inflammation and appetite regulation in this process?

SUMMARY. Mice with inducible, whole-body Atg7 deletion develop lethal cachexia characterized by hypophagia, tissue wasting, and systemic inflammation. Among several cytokines upregulated in these mice, only CCL2 (also known as MCP-1) is essential for driving disease. Genetic deletion of Ccl2 restores feeding, preserves body weight, and rescues survival. The underlying mechanism involves selective loss of hypothalamic neurons that express orexin and MCH—two neuropeptides critical for stimulating appetite and regulating energy balance. Single-nucleus RNA-seq suggests these neurons are absent in Atg7-deficient mice but preserved in Ccl2-deficient animals. Notably, CCL2 appears to originate from fibroblast-like stromal cells in the hypothalamus, highlighting a non-neuronal source of the neuroinflammatory insult. Pharmacologic blockade of CCL2 using a monoclonal antibody fails to rescue the phenotype, emphasizing the need for a deeper understanding of cytokine action in the CNS. Finally, deletion of leptin (ob/ob genotype) also rescues food intake and survival, underscoring anorexia as the critical effector of cachexia lethality in this model.

KEY RESULTS Whole-body Atg7 deletion causes cachexia and inflammation Figures 1A–J, Supp. Fig. S1 Mice exhibit rapid weight loss, muscle and fat depletion, liver inflammation, and elevated circulating cytokines, including CCL2.

CCL2 is essential for lethality in autophagy-deficient mice Figures 2A–B, Supp. Fig. S2 Among multiple cytokines tested (GDF15, CXCL10, CCL2), only Ccl2 deletion fully rescues survival and body composition.

CCL2 deletion restores hepatic function and fasting tolerance Figures 2C–I Ccl2−/−;Atg7Δ/Δ mice maintain glucose levels, survive fasting, and show normal gluconeogenesis, unlike their Atg7Δ/Δ counterparts.

CCL2 drives anorexia in autophagy-deficient mice Figures 3A–H Loss of Ccl2 restores food intake and total energy expenditure (TEE), confirming that CCL2 suppresses appetite.

CCL2 causes hypothalamic neuron loss Figures 4A–G, Supp. Fig. S3 Single-nucleus RNA-seq shows selective depletion of orexin and melanin-concentrating hormone (MCH) neurons—both central to appetite regulation—in Atg7Δ/Δ mice. This neuronal loss is fully reversed by Ccl2 deletion.

CCL2 is expressed in fibroblast cells in the hypothalamus, suggesting the potential source (Figure 4G).

Leptin deficiency restores survival despite persistent CCL2 elevation Figures 5A–I ob/ob;Atg7Δ/Δ mice survive, confirming that appetite suppression, not inflammation or weight loss per se, drives death.

Anti-CCL2 antibody fails to rescue cachexia Supp. Fig. S2G–J A neutralizing antibody against CCL2 (C1142) does not improve survival, highlighting differences between genetic and pharmacologic cytokine suppression.

STRENGTHS Uncovers a specific cytokine-neuron interaction driving lethal anorexia Demonstrates that preserving appetite alone is sufficient for survival Employs rigorous genetic models and multi-omic analysis Challenges the notion that cachexia is a purely metabolic disorder Provides a novel brain-centered mechanistic framework for systemic wasting

FUTURE WORK & EXPERIMENTAL DIRECTIONS Elucidate why CCL2 antibodies fail. Explore CCR2 signaling in the hypothalamus and its contribution to neuron loss Test whether this mechanism operates in more disease-relevant models: * • 5/6 nephrectomy (chronic kidney disease): features systemic inflammation and cachexia * • C26 or Lewis lung carcinoma (cancer cachexia): gold-standard models with upregulated CCL2 and appetite suppression * • SOD1-G93A (ALS model): mimics neuroinflammatory wasting * • Bleomycin-induced pulmonary fibrosis: induces systemic inflammation and muscle loss Use neuron-specific autophagy knockouts to dissect region-specific vulnerability Investigate sex differences and long-term behavioral recovery in Ccl2- or leptin-rescued mice

RELEVANCE TO RECENT LITERATURE This study complements recent work on inflammation-driven neurobehavioral deficits in cachexia: Zhu et al. (2025, Science) identified an IL-6–driven brainstem-to-basal ganglia circuit that suppresses motivation in cancer cachexia. In contrast, this preprint reveals CCL2-mediated destruction of hypothalamic appetite neurons, suggesting multiple inflammatory mediators act through distinct neuroanatomical routes to drive cachexia. Together, these findings support a growing model in which cachexia is driven by neuroimmune signaling.

AUTHORSHIP NOTE. This review was drafted with the assistance of ChatGPT (OpenAI) to organize and articulate key insights. Dr. Angela Andersen checked the final document.

FINAL TAKEAWAY. This preprint redefines cachexia as a neuroimmune syndrome, where CCL2—likely produced by fibroblasts in the hypothalamus – leads to the elimination of orexigenic neurons and lethal appetite suppression. By showing that rescuing food intake, rather than reversing metabolic derangements, is sufficient to prevent death, the authors shift our understanding of wasting from a metabolic imbalance to a brain-centered inflammatory pathology. These findings open new paths for preventing cachexia across diseases, but also highlight the complexity of translating cytokine-targeted therapies to the clinic.

for - adjacency - autophagy - transition to planet based diet - validation for flexitarian diet - TP cafe

All of these papers need checking - just in case. could it be related to the fact that the DMVs and autophagosomes have much in common?