Summary: A new study from the University of Michigan shows that the brain actively maintains blood glucose stability during ordinary daily conditions, not only during acute crises. Researchers identified a specific set of neurons in the ventromedial hypothalamus—VMHCckbr neurons—that help preserve blood sugar by promoting fat breakdown, particularly during the early hours of sleep. This lipolysis supplies glycerol, a substrate used for making glucose, preventing overnight hypoglycemia and ensuring a steady energy supply. The findings suggest that excessive activity of these neurons may contribute to elevated nighttime lipolysis seen in prediabetes, highlighting a more nuanced role for the brain in metabolic health.
Key Facts
- VMHCckbr neurons: A distinct population in the ventromedial hypothalamus that helps regulate blood glucose during routine, non-emergent conditions.
- Nighttime stability: These neurons act during the early sleep period to prevent overnight hypoglycemia by driving lipolysis and increasing glycerol availability for gluconeogenesis.
- Prediabetes link: Overactivity of this neuronal population could underlie increased nocturnal lipolysis and contribute to higher blood glucose in prediabetes.
Source: University of Michigan
The brain is known to mobilize glucose during emergencies such as hypoglycemia and during fasting, but relatively little has been established about its everyday role in maintaining glucose within a narrow physiological range. In work published in the journal Molecular Metabolism, researchers at the University of Michigan investigated how a defined set of hypothalamic neurons contributes to glucose regulation during normal daily rhythms, including the fasting interval that occurs overnight.
Prior research over several decades has shown that nervous system dysfunction can lead to blood glucose fluctuations, especially in diabetes. Many glucose-regulating neurons are located in the ventromedial nucleus of the hypothalamus (VMH), a brain region that also influences hunger, fear responses, temperature regulation and reproductive behaviors. Most earlier studies emphasized the VMH’s role in elevating blood sugar in acute stress. The current study asked whether VMH neurons also regulate glucose during routine conditions when diabetes typically develops.
The investigators focused on VMH neurons that express the cholecystokinin B receptor (VMHCckbr neurons). Using mouse models in which these neurons were chronically silenced, the team monitored continuous glucose levels to determine whether the cells are required to maintain glucose homeostasis during daily life and short fasting periods.
Results showed that VMHCckbr neurons support glucose stability during short overnight fasts. Rather than mobilizing glucose by depleting liver glycogen or by increasing classical gluconeogenic gene expression, these neurons prompt white adipose tissue to undergo lipolysis. The breakdown of fat releases glycerol into the circulation; glycerol then serves as a gluconeogenic substrate that helps maintain blood glucose in the early sleep period. Restoring glycerol availability reversed the drop in glucose that occurred when VMHCckbr neurons were silenced, confirming the substrate’s key role. Acute activation of these neurons mobilized additional gluconeogenic substrates beyond glycerol, indicating layered mechanisms depending on the context and neuronal activity level.
Mechanistically, the VMHCckbr neurons promote lipolysis through a pathway that depends on β3-adrenergic receptor signaling in adipose tissue. This specific coupling—neuronal activation to β3-AR–dependent fat breakdown—highlights how the brain can selectively recruit peripheral tissues to maintain metabolic balance during routine fasting and sleep.
The study’s findings have clinical implications. Patients with prediabetes often display increased nighttime lipolysis; the researchers propose that overactivity of VMHCckbr neurons could contribute to this pattern and thereby to elevated nocturnal glucose. Importantly, the VMHCckbr neurons appear to form a distinct subset among glucose-mobilizing VMH neurons, suggesting that different neuronal populations use separate mechanisms to tune glucose levels for the demands of fasting, feeding or stress. In other words, the brain’s control of glycemia is not a binary on/off system, but a flexible network that produces context-appropriate responses.
The research team is now working to map how multiple neuronal populations within the VMH coordinate their activity across different physiological conditions and how the broader nervous system interacts with key peripheral organs—such as the liver and pancreas—to regulate glucose. These efforts aim to clarify how neuronal circuits contribute to the progression from normal glucose control to metabolic disorders.
Study team and acknowledgments: The work was carried out by researchers at the Caswell Diabetes Institute and includes Alison Affinati, M.D., Ph.D., and co-authors Jiaao Su, Abdullah Hashsham, Nandan Kodur, Carla Burton, Amanda Mancuso, Anjan Singer, Jennifer Wloszek, Abigail J. Tomlinson, Warren T. Yacawych, Jonathan N. Flak, Kenneth T. Lewis, Lily R. Oles, Hiroyuki Mori, Nadejda Bozadjieva-Kramer, Adina F. Turcu, Ormond A. MacDougald and Martin G. Myers.
Funding and disclosures: Funding support came from the Michigan Diabetes Research Center (NIH P30 DK020572), the Mouse Metabolic Phenotyping Center — Live (U2CDK135066), the Michigan Nutrition and Obesity Center Adipose Tissue Core (P30 DK089503), the Department of Veterans Affairs (IK2BX005715), the Warren Alpert Foundation, the Endocrine Fellows Foundation, the Marilyn H. Vincent Foundation and Novo Nordisk, with additional support from NIH grant K08 DK1297226. Disclosures reported include relationships between some authors and pharmaceutical or biotech companies as noted by the investigators.
About this metabolism and neuroscience research news
Author: Ananya Sen
Source: University of Michigan
Contact: Ananya Sen, [email protected]
Image: Image credited to Neuroscience News
Original research (open access): “Control of physiologic glucose homeostasis via hypothalamic modulation of gluconeogenic substrate availability” by Alison Affinati et al., published in Molecular Metabolism. The study characterizes how VMHCckbr neurons regulate physiological glucose homeostasis by modulating glycerol availability and β3-adrenergic receptor–dependent lipolysis.
Abstract
Control of physiologic glucose homeostasis via hypothalamic modulation of gluconeogenic substrate availability
Objectives
The brain mobilizes glucose in emergency situations, such as hypoglycemia, and during routine physiological states like fasting. While many hypothalamic neurons that mobilize glucose also regulate other aspects of energy balance, VMH neurons that express the cholecystokinin B receptor (VMHCckbr) support glucose production during hypoglycemia without broadly altering energy homeostasis. Their role in everyday glucose physiology and the mechanisms they use to support glucose mobilization required clarification.
Methods
Continuous glucose monitoring was performed in mice with chronically silenced VMHCckbr neurons to determine their necessity for routine glucose homeostasis. The study combined chronic silencing using tetanus toxin–based approaches and acute optogenetic activation, followed by analyses of hepatic glucose metabolism and white adipose tissue lipolysis.
Results
VMHCckbr neurons were found to support glucose homeostasis during short fasts by promoting gluconeogenic substrate mobilization and lipolysis. These neurons increased circulating glycerol in a β3-adrenergic receptor–dependent manner without depleting hepatic glycogen or upregulating canonical gluconeogenic gene expression. Restoring glycerol availability corrected glucose deficits caused by neuronal silencing, and acute activation mobilized additional gluconeogenic substrates beyond glycerol.
Conclusions
VMHCckbr neurons comprise a distinct glucose-mobilizing population in the VMH that supports physiologic glucose homeostasis, likely through β3-AR–mediated substrate mobilization and lipolysis. The existence of multiple glucose-mobilizing neuronal populations that use different mechanisms depending on context provides the brain with the flexibility to coordinate appropriate glycemic responses under fasting, feeding and stress conditions.