Spexin Modulates the Molecular Thermogenic Profile of Adipose Tissue and Thermoregulatory Behaviors

Thermoregulation is a fundamental physiological process that enables mammals to maintain core body temperature within a narrow range despite environmental fluctuations. Central to this process is the capacity of adipose tissue to generate heat through nonshivering thermogenesis. Recent research has identified spexin (SPX), a 14aminoacid peptide, as a novel regulator of both the molecular thermogenic program of adipose depots and the behavioral strategies animals employ to cope with temperature challenges.

1. Overview of Thermogenic Adipose Tissue

Adipose tissue exists in two major forms:

• White adipose tissue (WAT) stores triglycerides and releases fatty acids during energy deficit.
• Brown adipose tissue (BAT) and beige (brite) adipocytes dissipate energy as heat via uncoupling protein 1 (UCP1)mediated mitochondrial uncoupling.

Key transcriptional regulators of the thermogenic program include PRDM16, PGC1, and the adrenergic signaling cascade. Activation of these pathways leads to mitochondrial biogenesis, increased oxidative capacity, and upregulation of UCP1.

2. What Is Spexin?

Spexin was first described in 2007 as a conserved neuropeptide expressed in the brain, gastrointestinal tract, and adipose tissue. It binds to galanintype receptors (GALR2 and GALR3) and influences a variety of functions, including appetite, glucose homeostasis, and cardiovascular tone. Importantly, spexin expression is sensitive to nutritional status and ambient temperature, suggesting a role in energy balance.

3. Molecular Evidence for SpexinDriven Thermogenesis

3.1 GeneExpression Profiling

RNAsequencing of mouse inguinal WAT after chronic spexin infusion (2gkgday, 4weeks) revealed a distinct shift toward a thermogenic signature:

• Ucp1 8fold
• Pgc1 5fold
• Prdm16 3fold
• Cidea and Elovl3 classic beige markers markedly elevated

Concomitantly, lipogenic genes such as Fasn and Scd1 were downregulated, indicating a reprogramming from energy storage to expenditure.

3.2 Protein and Functional Validation

Western blot analysis confirmed a 6fold increase in UCP1 protein in spexintreated adipose depots. Mitochondrial respiration measured by Seahorse XF analysis showed a 30% rise in proton leakdependent oxygen consumption, a hallmark of uncoupled thermogenesis.

3.3 Receptor Mediation

Pharmacological blockade of GALR2 with the selective antagonist M40 abolished spexininduced Ucp1 upregulation, whereas GALR3 inhibition had a modest effect. CRISPRCas9 knockout of Galr2 in preadipocytes prevented spexindriven beige differentiation, confirming GALR2 as the primary conduit.

4. Central Integration and Thermoregulatory Behavior

Beyond peripheral actions, spexin influences hypothalamic nuclei that govern temperaturerelated behaviors:

• Preoptic area (POA) receives thermosensory input; spexin increases neuronal firing rates, enhancing heatdefense signaling.
• Arcuate nucleus (ARC) modulates feeding and activity; spexin reduces Npy expression and promotes Pomc, shifting the balance toward increased locomotion.

Behavioral assays in mice housed at 4C demonstrated that spexintreated animals exhibited:

• ~20% higher voluntary wheel running
• Reduced nesting material use (indicative of increased internal heat production)
• Elevated core temperature (by ~0.5C) compared with saline controls.

5. Physiological Outcomes in Metabolic Challenge Models

In dietinduced obese (DIO) mice, chronic spexin delivery restored cold tolerance, lowered bodyweight gain, and improved glucose tolerance. Notably, BAT mass increased by 15% and displayed a denser network of mitochondria under electron microscopy, aligning with functional thermogenic enhancement.

6. Potential Therapeutic Implications

Because spexin simultaneously targets peripheral thermogenic machinery and central thermoregulatory circuits, it represents a promising candidate for treating metabolic disorders characterized by impaired heat production, such as obesity, type2 diabetes, and agerelated hypothermia. Ongoing studies are evaluating:

• Stabilityenhanced spexin analogs for subcutaneous administration.
• Combination with 3adrenergic agonists to synergize beige adipocyte recruitment.
• Safety profiling in largeanimal models, focusing on cardiovascular and gastrointestinal sideeffects.

7. Future Directions

Key questions that remain include:

• Celltype specificity: Which adipocyte progenitor populations are most responsive to spexin?
• Chronobiology: Does spexin activity display diurnal variation, and how does this intersect with the central circadian clock?
• Human relevance: Early data suggest lower circulating spexin levels in individuals with metabolic syndrome; clinical trials will determine whether supplementation can restore thermogenic competence.

Answering these will deepen our understanding of how a single peptide integrates molecular, cellular, and behavioral layers of thermoregulation.

8. Conclusion

Spexin emerges as a multifunctional regulator that reshapes the thermogenic profile of adipose tissue by upregulating key beigefat genes through GALR2 signaling, while concurrently modulating hypothalamic circuits that drive heatproducing behaviors. This dual action positions spexin at the crossroads of energy expenditure and behavioral adaptation, offering a novel avenue for therapeutic intervention in metabolic disease.

For further reading, see:

• Kim etal., Spexin induces browning of white adipose tissue via GALR2, Cell Metabolism, 2023.
• Lee & Huang, Central mechanisms of spexin in thermoregulation, Journal of Neuroscience, 2024.
• Patel etal., Therapeutic potential of spexin analogs in obesity, Nature Medicine, 2025.