Guardians of Metabolic Balance: How SerpinB2 Shields Tissue-Resident Macrophages from Mitochondrial Collapse in Chronic Inflammation

Overview

Visceral adipose tissue (VAT) is an immunologically active organ where protective tissue-resident macrophages (TRMs) maintain tissue homeostasis, while recruited monocyte-derived macrophages (MDMs) promote inflammation. Although MDM-driven inflammation during obesity is well-characterized, the survival mechanisms of protective TRMs during metabolic stress remain poorly understood.

Addressing this scientific gap, a study published in Nature Communications (2026) by Dutta et al., titled "Tissue-resident macrophage survival depends on mitochondrial function regulated by SerpinB2 in chronic inflammation," reveals how TRMs survive. Using preclinical models and human omental adipose tissue, the authors demonstrate that the intracellular protein SerpinB2 regulates mitochondrial function in TRMs, preserving this protective cell population to counter chronic inflammation and systemic insulin resistance.

Highlights

• Advanced In Vivo Fate Mapping and Imaging: By combining parabiosis (surgically joining CD45.1 and CD45.2 mice to track long-term cell chimerism) with high-resolution two-photon intravital imaging, the team captured real-time macrophage dynamics within gonadal adipose tissue and verified that recovering TRMs originate from local self-renewal rather than circulating monocytes.
• Optogenetic Subpopulation Targeting: The researchers used an innovative LysM-Cre/ChR2 mouse model to selectively eliminate resident macrophages via blue light exposure (BLE) rather than white light exposure (WLE), proving their direct contribution to metabolic health without relying on global chemical depletion.
• Gold-Standard Metabolic Clamping: The team utilized jugular vein catheterization to perform hyperinsulinemic-euglycemic clamp studies—the most definitive method in metabolic research—to directly measure in vivo insulin sensitivity and endogenous hepatic glucose production.
• The IFN-γ-Ikaros-SerpinB2 Axis: The study identifies a non-canonical, intracellular role for SerpinB2 (encoding PAI-2) as a mitochondrial protector, mapping the exact transcriptional suppression pathway where systemic IFN-γ elevation induces Ikaros to bind to the SerpinB2 promoter and silence its expression in chronic obesity.
• Mitochondrial Respiration and Inflammatory Control: Using Seahorse metabolic flux analysis, the authors proved that hyperactive oxygen consumption rates (OCR) in macrophages directly fuel systemic inflammation, representing a paradigm shift in immunometabolism.
• Practical Mitochondrial Rescue Strategies: The study demonstrated that both genetic receptor deletion and simple oral supplementation with N-acetylcysteine (NAC), a glutathione (GSH) precursor, can rescue this protective immune cell population, prevent mitochondrial collapse, and restore metabolic homeostasis.

Key Findings

The research team performed a series of highly detailed in vivo and in vitro experiments to understand the survival and anti-inflammatory mechanisms of TRMs.

• Transcriptomic Divergence and Apoptosis-Driven Loss of Adipose Macrophages

Using CX3CR1-GFP/tdTomato fate-mapping and parabiosis, the authors confirmed that CX3CR1⁺ CCR2⁺ cells represent short-lived MDMs, while CX3CR1^- CCR2^- cells are long-term, self-renewing TRMs. RNA sequencing showed distinct transcriptomes: MDMs expressed pro-inflammatory genes linked to insulin resistance, whereas TRMs expressed insulin-sensitizing, anti-inflammatory markers. Correspondingly, obese human visceral adipose tissue (VAT) showed a marked loss of protective CCR2^- TRMs alongside MDM accumulation.

In mice, high-fat diet (HFD) feeding triggered a progressive, apoptosis-driven decline in these protective TRMs, as evidenced by elevated active caspase-3 and annexin V. Notably, this decline is reversible; withdrawing the HFD restored the TRM pool via local proliferation (Ki-67⁺) rather than circulating monocyte recruitment.

Fig.1 Resident and monocyte-derived macrophages in visceral fat show distinct immune and metabolic features during obesity progression. (Vasamsetti, et al., 2026)

• Optogenetic Depletion of TRMs Worsens Insulin Resistance

Optogenetic depletion of VAT TRMs using BLE in LysM-Cre/ChR2 mice severely impaired glucose tolerance and insulin sensitivity, raising serum triglycerides (TG), free fatty acids (FFA), and free glycerol (FG). Depletion impaired insulin signaling (decreased pAkt/Glut4) and glucose-clearance gene expression while elevating pro-inflammatory cytokines.

Fig.2 Loss of resident macrophages in visceral fat worsens inflammation and metabolic dysfunction in obese mice. (Vasamsetti, et al., 2026)

• SerpinB2 Protects the Mitochondrial Integrity of TRMs

RNA sequencing identified SerpinB2 (encoding intracellular PAI-2) as highly and uniquely enriched in TRMs. Human TRMs displayed a similar enrichment. However, obesity significantly downregulated SerpinB2 in both mouse and human TRMs, with expression negatively correlating with body mass index (BMI). Palmitate treatment similarly suppressed SerpinB2 in bone marrow-derived macrophages (BMDMs).

Fig.3 SerpinB2 is highly expressed in resident adipose macrophages and declines with obesity related inflammation. (Vasamsetti, et al., 2026)

• The IFN-γ-Ikaros Signaling Axis Drives SerpinB2 Downregulation

Elevated interferon-gamma (IFN-γ) in obese adipose tissue drives SerpinB2 silencing. Mechanistically, IFN-γ induces the transcriptional suppressor Ikaros to bind the SerpinB2 promoter, suppressing its transcription, whereas the Ikaros inhibitor lenalidomide rescues expression. Consequently, myeloid-specific IFN-γ receptor 1 (Ifngr1) deficiency prevents TRM apoptosis and improves systemic metabolism on HFD. Conversely, SerpinB2 deletion causes mitochondrial dysfunction, cytochrome c leakage, and caspase-3-mediated cell death.

Fig.4 IFN γ signaling reduces SerpinB2 expression and promotes macrophage apoptosis in obese adipose tissue. (Vasamsetti, et al., 2026)

• Mitochondrial ROS and Cytochrome c Leakage Drive Apoptosis in the Absence of SerpinB2

Without SerpinB2, mitochondrial cytochrome c leaks into the cytoplasm. Healthy TRMs are normally enriched with antioxidant genes (e.g., Sod3, Gst family, Mgst1, Mt1/2, Gpx7, Me1, Idh2) and the glutamic acid transporter Slc7a13 to synthesize glutathione (GSH). In obesity, this antioxidant defense declines, correlating with glucose intolerance.

SerpinB2 deficiency reduces these antioxidants, generating mitochondrial reactive oxygen species (ROS) that trigger apoptosis. Scavenging mitochondrial ROS with mitotempol prevents cytochrome c leakage and apoptosis, confirming ROS as the primary driver of cell death.

Fig.5 Increased mitochondrial oxidative stress drives apoptosis in SerpinB2-deficient macrophages. (Vasamsetti, et al., 2026)

• Hyperactive Mitochondrial Respiration and Myeloid SerpinB2 Deficiency Drive Systemic Metabolic Collapse

Obese macrophages exhibit hyperactive oxygen consumption rates (OCR) that fuel inflammatory cytokine release. Inhibiting mitochondrial respiration in myeloid cells (LysM-Cre/Cox10-fl/fl) suppresses this inflammation and improves insulin sensitivity. Conversely, SerpinB2 deficiency accelerates OCR and exacerbates inflammation, whereas its overexpression suppresses inflammation.

Myeloid-specific SerpinB2 deficiency (LysM-Cre/SerpinB2-fl/fl) triggers systemic insulin resistance, glucose intolerance, and elevated lipids. Hyperinsulinemic-euglycemic clamps showed a reduced glucose infusion rate (GIR) and impaired suppression of hepatic glucose production, alongside compromised tissue insulin signaling. Remarkably, administering IL-4 (naturally secreted by TRMs) completely reversed this metabolic dysfunction.

Fig.6 SerpinB2 deficiency enhances inflammatory activity and impairs metabolic regulation in obesity. (Vasamsetti, et al., 2026)

• Adipose Resident Macrophages and GSH Confine Pathogenic Adipocyte Hypertrophy

TRM depletion or myeloid SerpinB2 deficiency caused VAT expansion, adipocyte hypertrophy, and altered cytoskeletal remodeling. Adipocytes adjacent to CCR2- TRMs remained smaller, as TRMs express low levels of the hypertrophic factor Il1b and high levels of the inhibitor Tgfb2.

These size-limiting effects are mediated by GSH; the GSH precursor NAC blocked 3T3-L1 adipocyte differentiation in vitro. In vivo, oral NAC supplementation in obese LysM-Cre/SerpinB2-fl/fl mice reduced body weight, restored glucose tolerance, and rescued the TRM population from apoptosis. Conditioned media experiments confirmed that GSH-stimulated TRM secretions directly prevent pathogenic adipocyte hypertrophy.

Fig.7 Glutathione signaling limits adipocyte enlargement and visceral fat expansion during obesity. (Vasamsetti, et al., 2026)

Interpretation & Translational Value

This study reveals a key mechanism linking chronic inflammation to metabolic dysfunction, showing how the loss of protective TRMs drives systemic insulin resistance. By identifying the IFN-γ-Ikaros-SerpinB2-GSH axis, the authors highlight new therapeutic targets for type 2 diabetes and obesity-associated metabolic syndrome.

Therapies designed to inhibit the transcriptional suppressor Ikaros, block IFN-γ signaling in myeloid cells, or support mitochondrial antioxidant pathways could help preserve protective TRMs during chronic inflammation.

Furthermore, the discovery that oral administration of the GSH precursor NAC restores the resident macrophage pool and improves insulin sensitivity offers a practical, translatable therapeutic strategy. This mitochondrial rescue approach could also be applied to other inflammatory diseases where tissue-resident macrophages are lost, such as myocardial infarction and Alzheimer's disease.

Research Support

To accelerate your immunometabolism research, Protheragen offers gold-standard preclinical services modeled after this study's key methodologies. We provide hyperinsulinemic-euglycemic clamps to assess insulin sensitivity, Seahorse XF96 bioenergetics for real-time mitochondrial analysis, and multicolor flow cytometry for resident macrophage sorting. Additionally, we support advanced confocal/two-photon tissue imaging, custom knockout models, optogenetics, and pharmacological interventions (HFD, IL-4, or NAC) to deliver reproducible translational data.

Insulin Testing Service		Obesity Gene Knockout Service
Obesity Physiology and Biochemistry Analysis Service		Obesity Tissue Cell Function Analysis Service
Obesity Pathobiology Research Service		Glucose Metabolism Analysis Service
Adipose Tissue Inflammation Analysis Service		Inflammatory Cytokine Analysis Service