Bone marrow-derived Ly6C− macrophages promote ischemia-induced chronic kidney disease

Abstract

Macrophages play an important role in renal injury and repair after acute kidney injury (AKI) and the subsequent chronic kidney disease (CKD) that often results. However, as macrophages have a high degree of plasticity and heterogeneity, the function(s) of macrophage subtypes in AKI-to-CKD progression are not fully understood. Here, we focused on Ly6C − macrophages, which are derived from the embryonic yolk sac and post-development become resident in the kidneys. We found that C–C chemokine receptor type 2 (CCR2) deficiency, which blocks the migration of Ly6C + macrophages from the bone marrow to the sites of injury, alleviated ischemia-induced AKI in mice. Unexpectedly, though, CCR2 deficiency worsened the subsequent renal fibrosis, which was marked by notable intra-renal infiltration of Ly6C − macrophages. These Ly6C − macrophages were greater in number in both the acute and chronic phases after ischemia reperfusion (I/R) in kidneys of wild type (WT) mice, and we showed them to be derived from the bone marrow by bone marrow chimerism. Clodronate Liposomes (CLs)-mediated depletion of renal Ly6C − macrophages in CCR2 − /− mice or in WT mice after I/R alleviated the renal injury and fibrosis. On the contrary, adoptive transfer of Ly6C − macrophages from injured kidneys of WT mice into immune-deficient mice was sufficient to induce renal injury and fibrosis. Transcriptome sequencing of Ly6C − macrophages from injured kidneys revealed that they secreted various cytokines and growth factors, which were associated with the transdifferentiation of fibroblasts into myofibroblasts. This transdifferentiation effect was further supported by in vitro studies showing that Ly6C − macrophages induced the secretion of extracellular matrix proteins from co-cultured fibroblasts. In conclusion, the presence of bone marrow-derived Ly6C − macrophages after ischemia induces AKI and worsens subsequent CKD.

Lymphatic Vessels Enhancing Adaptive Immunity Deteriorates Renal Inflammation and Renal Fibrosis

“…Our research team sorted out Ly6C-macrophages in mice kidney at 5 days after IR operation and injected them under the renal capsule of mice with immune deficiency, finding that the original normal kidney showed damage and intrarenal fibrosis 5 days later, suggesting that Ly6C-macrophages directly damaged kidney and induced subsequent fibrosis [38]. We further identified that Ly6C− macrophages were the dominant intrarenal macrophages after ischemia-reperfusion injury, especially at the chronic phase, and most were derived from the bone marrow and depended on intrarenal CX3CL1-CX3CR1 interaction [38].…”

The Impact of Versatile Macrophage Functions on Acute Kidney Injury and Its Outcomes

“…Whereas a number of studies have claimed that both CSF-1 and -2 drive M2 skewing of Mϕ in mice with AKI (Zhang et al, 2012; Huen et al, 2015; Wang et al, 2015), it was controversially found that IL-34, another ligand for CSF-1R, does not polarize Mϕ in murine AKI (Baek et al, 2015) and lupus model (Wada et al, 2019), indicating that CSF-1R signaling is dispensable in M2 Mϕ polarization. Supportive of this data, other studies have shown that: (1) increased CSF-1 expression in the resolution phase of AKI is not sufficient to prevent Mϕ from M1 polarization when Mϕ are exposed to an M1 stimulus or when they are deprived of an M2 stimulus during AKI (Fujiu et al, 2011; Susnik et al, 2014; Chiba et al, 2016); (2) quiescent and M2 Mϕ in the resolution phase of AKI differ in transcriptional profiles and functions (Lever et al, 2019; Yang et al, 2019); and (3) the sustained blockage of CSF-1R or the constitutive deletion of CSF-1 ameliorates AKI (Lenda et al, 2003; Ma et al, 2009; more discussion in Assessing M ϕ functions by depleting M ϕ section). Nevertheless, what is consistent throughout all studies (Zhang et al, 2012; Baek et al, 2015; Huen et al, 2015; Wang et al, 2015; Chiba et al, 2016) is that the deficiency in Mϕ survival factors reduces the number of Mϕ (including that of M2 Mϕ predominating in the resolution phase of AKI).…”

“…The migration of Ly6C high monocytes to the site of inflammation occurs through chemotactic mechanisms (e.g., via CCR2 and CX 3 CR1). Therefore, deletion or blockage of chemotaxis receptors on monocytes is found to be protective against ischemia-induced AKI in mice (Furuichi et al, 2003; Li et al, 2008; Lu et al, 2008; Oh et al, 2008; Yang et al, 2019). Monocyte infiltration occurs in the first 48 h (Lu et al, 2008) and completely ceases before day 3 of AKI.…”

“…Several studies have shown that monocyte-derived Ly6C int and Ly6C low Mϕ populations display transcriptionally and functionally distinct M2 phenotypes, both implicated in immunosuppression and tissue regeneration. In the later stages of AKI, Ly6C low Mϕ predominate over Ly6C int Mϕ and are found to promote interstitial fibrosis (Lin et al, 2009; Clements et al, 2016; Lever et al, 2019; Yang et al, 2019) (Figure 4). More recent studies revealed that quiescent tissue-resident Mϕ remain in the tissue independently of monocyte-derived Ly6C low Mϕ (Lin et al, 2009; Zhang et al, 2012; Lever et al, 2019) and are reprogramed in AKI toward a developmental state resembling perinatal Mϕ (Schulz et al, 2012; Mass et al, 2016), which are implicated in early kidney development (Lever et al, 2019).…”

“…However, it is to note that M2 Mϕ are considered to be instrumental in the development of pathological fibrosis and the progression of CKD (Duffield, 2010; Anders and Ryu, 2011). Especially, several studies have identified monocyte-derived Ly6C low Mϕ, which predominate over Ly6C int Mϕ in the later stages of AKI, as direct or indirect contributors to interstitial fibrosis (Lin et al, 2009; Anders and Ryu, 2011; Clements et al, 2016; Lever et al, 2019; Yang et al, 2019) and as a hallmark of CKD progression post-AKI. In line with this, CX 3 CL1-CX 3 CR1-mediated survival of Ly6C low Mϕ correlates with interstitial fibrosis in obstructed kidneys (Peng et al, 2015).…”