Angiopoietin-2 and Progressive Kidney Disease

CKD is sustained by a maladaptive interaction between inflammation, microvascular dysfunction, tubular injury, and fibrosis. The study by Luo et al., “Cell-Specific Roles of Angiopoietin-2 in CKD,”¹ published in this issue of JASN, provides an important advance by moving the field beyond the concept of angiopoietin-2 (ANGPT2) as a general marker of endothelial activation and toward a more nuanced understanding of ANGPT2 as a temporally and spatially regulated driver of CKD progression (Figure 1).

ANGPT2 was originally identified as a context-dependent antagonist of angiopoietin-1 (ANGPT1)–mediated signaling through the receptor tyrosine kinase tyrosine kinase with immunoglobulin and epidermal growth factor homology domains 2 (TIE2), a pathway central to vascular stability, endothelial quiescence, and barrier integrity.^2,3 In healthy vessels, ANGPT1 supports TIE2 activation and endothelial homeostasis, whereas ANGPT2 is rapidly induced during vascular stress, inflammation, and remodeling. In kidney disease, this balance is particularly relevant because the kidney depends on highly specialized microvascular beds, including fenestrated glomerular and peritubular capillaries, to maintain filtration, oxygen delivery, and tubular function. Consistent with a protective role for TIE2 signaling, inducible deletion of either Angpt1 or Tie2 exacerbates kidney injury, microvascular loss, and fibrosis in experimental models of CKD, highlighting the protective role for ANGPT1-TIE2 signaling for renal vascular and tissue homeostasis.^4,5

The major contribution of Luo et al. is the demonstration that the pathogenic role of ANGPT2 in CKD depends on its cellular source. Using human kidney transcriptomic data and mouse models with global, endothelial cell–specific, and tubular epithelial cell–specific Angpt2 deletion, the authors show that increased kidney ANGPT2 expression associates with lower eGFR, greater fibrosis, and worse kidney outcomes. Global Angpt2 deletion protected against kidney dysfunction, inflammation, vascular rarefaction, and fibrosis. However, endothelial and tubular epithelial ANGPT2 had distinct roles: Endothelial ANGPT2 promoted early endothelial activation and inflammatory signaling, whereas tubular epithelial ANGPT2 contributed more prominently to later functional decline, vascular injury, and fibrosis.

This distinction is highly important for therapeutic development. Many approaches to ANGPT2 biology have treated ANGPT2 as a uniform pathogenic ligand. However, the kidney is not a single-compartment organ. Endothelial-derived ANGPT2 may act early as a destabilizing vascular signal, facilitating leukocyte recruitment, endothelial activation, and microvascular dysfunction. In contrast, tubular epithelial ANGPT2 may represent a later paracrine or injury-amplifying signal that links maladaptive tubular repair to interstitial inflammation, capillary loss, and matrix deposition. Thus, the same molecule may have different pathologic meanings depending on when and where it is expressed.

The findings also help reconcile earlier observations. Circulating and urinary ANGPT2 levels in patients with CKD have been associated with diabetic kidney disease, albuminuria, CKD progression, cardiovascular events, and adverse outcomes.^6,7 Experimental studies have shown that ANGPT2 inhibition can attenuate kidney fibrosis, in part by reducing endothelial apoptosis, chemokine signaling, and inflammatory cell recruitment.⁸ More recently, therapeutic TIE2 activation by antibody-clustered endogenous ANGPT2 was shown to prevent capillary loss and fibrosis in experimental kidney disease, suggesting that ANGPT2 biology can be therapeutically redirected rather than simply neutralized.⁴ Together, these studies support the view that ANGPT2 is not merely a biomarker but also a mechanistic node linking vascular instability to progressive kidney injury.

A key translational implication of these findings is that the therapeutic efficacy of ANGPT2-targeted interventions may require attention to disease stage and the cellular source of ANGPT2. During the early phases of CKD, when endothelial dysfunction, capillary instability, and inflammation are prominent, ANGPT2-targeted interventions may preserve microvascular integrity, maintain endothelial quiescence, and prevent the amplification of tissue injury. Consistent with this concept, recent work has demonstrated that blocking of ANGPT2 and/or activation of endothelial TIE2 signaling in experimental CKD protects the kidney microvasculature, suppresses downstream profibrotic pathways, and attenuates fibrosis progression.^4,8 However, in advanced stages of CKD, characterized by established capillary rarefaction and an injured tubular epithelium that becomes an active source of profibrotic mediators, it remains unclear whether vascular-protective therapies alone are sufficient to halt disease progression. In this setting, therapeutic strategies that simultaneously target endothelial dysfunction and maladaptive tubular injury pathways may be required to achieve meaningful clinical benefit. A better understanding of the temporal and cell-specific roles of ANGPT2 throughout CKD progression will therefore be essential for optimizing therapeutic strategies and identifying patients most likely to benefit from ANGPT2-directed interventions.

The study also raises important questions. First, what regulates the switch from endothelial to tubular ANGPT2 dominance during CKD progression? Hypoxia, oxidative stress, inflammatory cytokines, metabolic stress, and maladaptive repair pathways are plausible candidates. Second, through which mechanisms do tubular-derived ANGPT2 exert its effects? Although signaling through endothelial TIE2 remains likely, other cell types including subsets of TIE2-expressing macrophages and pericytes warrant further investigation. ANGPT2 may also act via noncanonical receptors such as integrins or through TIE2-independent mechanisms. Although ANGPT2-mediated integrin activation is well established,⁹ its role in CKD progression remains insufficiently explored. Moreover, TIE2-independent actions of ANGPT2 may contribute to disease pathogenesis. For example, ANGPT2 can bind thrombomodulin and inhibit its anticoagulant activity, potentially disrupting anticoagulant, anti-inflammatory, and endothelial barrier–protective pathways that are critical for maintaining microvascular homeostasis.¹⁰ Third, can emerging technologies such as spatial transcriptomics, single-cell multiomics, and urinary biomarker profiling be leveraged to identify patients in whom endothelial-derived versus tubular-derived ANGPT2 programs predominate? Such approaches could facilitate patient stratification and guide the development of precision therapies targeting ANGPT2 signaling in CKD.

In conclusion, Luo et al. provide a conceptual framework in which ANGPT2 expression is not simply high or low in CKD, but cell-specific, stage-dependent, and mechanistically informative. This is critical for improving treatment of kidney disease. Understanding the source and timing of ANGPT2 expression may guide patient stratification, therapeutic timing, and the design of interventions that restore vascular stability, prevent capillary rarefaction, and interrupt the transition from kidney injury to fibrosis.