Brain Cells Have a Fat Sensor That Keeps Their Recycling Plants Running

Deep inside the brain, a small cluster of neurons works around the clock to decide whether the body should eat, burn, or store energy. These hypothalamic neurons are famously sensitive to hormones and nutrients, but the molecular machinery that lets them sense fat and act on that information has remained only partly mapped. A new study published in Cellular and Molecular Life Sciences adds a surprising piece to the puzzle: a lipid-handling protein called CPT1C acts as a nutrient-sensitive guardian of the endolysosomal system, the cellular network that recycles waste and sorts molecular cargo. When CPT1C is missing or overwhelmed by dietary fat, the consequences ripple through the entire waste-management system of the neuron.

The research, led by Ana Cristina Reguera and Rosalía Rodríguez-Rodríguez at the Universitat Internacional de Catalunya, together with colleagues in Spain, Austria, and the United Kingdom, focuses on an unusual phospholipid known as bis(monoacylglycero)phosphate, or BMP. Unlike most cellular lipids, BMP is not scattered across membranes; it is almost exclusively found in late endosomes, the acidic compartments where cellular cargo is sorted, degraded, and recycled. BMP is required for the formation of intraluminal vesicles, the small bubbles that carry cargo into the interior of these compartments, and it plays a central role in cholesterol handling and lysosomal function. Without adequate BMP, the late endosomal system essentially loses its operating fluid.

What has puzzled researchers is how neurons maintain the right amount of this specialized lipid. BMP is chemically unusual, resistant to many common phospholipases, but it does have one known executioner: an enzyme called ABHD6, alpha-beta hydrolase domain containing 6. ABHD6 can hydrolyze BMP, breaking it down. The new work shows that the activity of this hydrolase is not constant; it is tuned by the metabolic state of the cell, and the tuning knob is CPT1C, a brain-specific member of the carnitine palmitoyltransferase family that sits in the endoplasmic reticulum and is known to respond to nutrient and energy cues.

CPT1C is an intriguing protein in its own right. Unlike its relatives CPT1A and CPT1B, which drive fatty acid import into mitochondria, CPT1C has negligible transferase activity. Instead, it behaves as a lipid and energy sensor, accumulating in neurons during fasting and low-energy states and helping neurons adapt their metabolism accordingly. The new study reveals an unexpected downstream target for this sensor: by restraining ABHD6, CPT1C protects the BMP pool that late endosomes depend on. In other words, a protein long studied for its role in energy sensing turns out to be a critical regulator of the lipid composition of the degradative compartments themselves.

The experimental logic of the study is straightforward and compelling. When the researchers removed CPT1C from neurons, ABHD6 activity rose, intracellular BMP levels fell, and the endolysosomal system began to falter. The consequences were measurable at several points along the pathway. Endosomal maturation was impaired, meaning early endosomes failed to progress properly into functional late compartments. The release of extracellular vesicles, including exosomes, which bud from late endosomes and depend on intraluminal vesicle formation, was reduced. Lysosomes lost their normal acidity, and their proteolytic activity, the enzymatic digestion of cargo, declined. Each of these defects is consistent with a shortage of the BMP that late endosomes and lysosomes need to build and maintain their internal architecture.

Crucially, the team showed that the problem was not a failure to synthesize BMP but an acceleration of its destruction. When they acutely inhibited ABHD6 in CPT1C-deficient neurons, BMP levels recovered, and the endolysosomal defects were rescued. This pharmacological rescue is one of the strongest signals in the paper, because it establishes a clear causal chain: CPT1C loss elevates ABHD6 activity, elevated ABHD6 depletes BMP, and BMP depletion undermines endolysosomal function. Blocking the hydrolase reverses the cascade at its source.

The nutrient dimension of the story emerged when the researchers exposed cells and animals to lipid overload. In wild-type neurons and in the hypothalamus of mice fed excess fat, ABHD6 activity increased and BMP levels dropped, mirroring the phenotype seen in CPT1C-deficient cells. But there was a telling difference: CPT1C-deficient neurons and mice already displayed constitutively elevated ABHD6 activity, and when faced with additional lipid excess, they failed to adapt further. Their regulatory range was exhausted. This suggests that CPT1C does not merely set a baseline for BMP homeostasis; it provides the adaptive capacity that neurons need when the lipid environment changes, as it does in high-fat diets and obesity.

Why does this matter for whole-body metabolism? The hypothalamus is the command center that integrates hormonal and nutrient signals to regulate food intake, energy expenditure, and glucose homeostasis. If lipid overload degrades the endolysosomal health of hypothalamic neurons, it could compromise the very cells responsible for sensing metabolic state and orchestrating the response. Defective lysosomal acidification and proteolysis would impair the degradation of proteins and organelles, including through autophagy, while reduced exosome release could alter intercellular communication within hypothalamic circuits. The study does not claim to have demonstrated these downstream physiological effects, but it establishes the molecular lesion, BMP depletion through unrestrained ABHD6, that could plausibly feed into hypothalamic dysfunction in metabolic disease.

The findings also connect to a broader and rapidly growing literature on lysosomal lipids in neurobiology. BMP has attracted intense interest because it is the receptor for a family of DNAJ proteins that stimulate lysosomal activity, and because altered BMP metabolism has been implicated in neurodegenerative conditions in which lysosomal failure is a hallmark. Neurons are particularly vulnerable to lysosomal dysfunction because they are long-lived and cannot dilute accumulated damage by cell division. A pathway in which a nutrient sensor controls the abundance of the signature lipid of the degradative pathway therefore offers a direct mechanistic bridge between diet, neuronal metabolism, and cellular housekeeping.

Therapeutically, the study points to ABHD6 as a druggable node. Pharmacological ABHD6 inhibition restored BMP levels in CPT1C-deficient neurons, raising the possibility that modulating this hydrolase could protect endolysosomal function in settings of chronic lipid excess. ABHD6 inhibitors have already been explored in other contexts, including endocannabinoid signaling, which gives medicinal chemists a starting point. The authors caution, implicitly, that much remains to be worked out: how CPT1C physically restrains ABHD6, whether the axis operates in other neuronal populations, and whether restoring BMP in vivo can correct hypothalamic dysfunction in obesity models. But the identification of a nutrient-sensitive CPT1C-ABHD6 axis governing BMP homeostasis gives researchers a concrete molecular handle on a process that had been almost entirely opaque. It reframes CPT1C not just as a metabolic sensor at the endoplasmic reticulum but as a custodian of the neuronal recycling system, and it suggests that the road from a fatty diet to faulty cellular waste disposal in the brain may run through a single, targetable enzyme.

Subject of Research: Nutrient-sensitive regulation of BMP lipid homeostasis and endolysosomal function in hypothalamic neurons via the CPT1C-ABHD6 axis

Article Title: A nutrient-sensitive CPT1C-ABHD6 axis regulates BMP homeostasis and endolysosomal function in hypothalamic neurons

Article References: Reguera, A. C., Miralpeix, C., Bernard, M., Zagmutt, S., Bolaños-Hurtado, M., Palacín, C., Fuentes, A., Rodríguez-García, M., Fosch, A., Garcia-Chica, J., Barnadas-Rodríguez, R., Fawzy, N., Zimmermann, R., Eden, E., Casals, N., & Rodríguez-Rodríguez, R. (2026). A nutrient-sensitive CPT1C-ABHD6 axis regulates BMP homeostasis and endolysosomal function in hypothalamic neurons. Cellular and Molecular Life Sciences. https://doi.org/10.1007/s00018-026-06451-3

Image Credits: AI Generated

DOI: 10.1007/s00018-026-06451-3

Keywords: CPT1C, ABHD6, BMP, endolysosomal system, hypothalamus, neurons, lipid metabolism, lysosomes, nutrient sensing, exosomes, obesity, endosomes