Kidney resident macrophages in the rat have minimal turnover and replacement by blood monocytes

Activation of platelets and the complement system in mice with Schistosoma-induced pulmonary hypertension

Schistosomiasis-induced pulmonary hypertension (PH) presents a significant global health burden, yet the underlying mechanisms remain poorly understood. Here, we investigate the involvement of platelets and the complement system in the initiation events leading to Schistosoma-induced PH. We demonstrate that Schistosoma exposure leads to thrombocytopenia, platelet accumulation in the lung, and platelet activation. In addition, we observed increased plasma complement anaphylatoxins C3a and C5a, indicative of complement system activation, and elevated platelet expression of C1q, C3, decay activating factor (DAF), and complement C3a and C5a receptors. Our findings suggest the active involvement of platelets in responding to complement system signals induced by Schistosoma exposure and form the basis for future mechanistic studies on how complement may regulate platelet activation and promote the development of Schistosoma-induced PH.NEW & NOTEWORTHY Schistosomiasis-induced pulmonary hypertension (PH) is a significant global health burden, yet the underlying mechanisms remain poorly understood. We demonstrate that Schistosoma exposure leads to platelet accumulation in the lung and platelet activation. We observed increased plasma levels of C3a and C5a, indicative of complement system activation, and elevated expression of platelet complement proteins and receptors. These findings underscore the role of platelets and complement in the inflammatory responses associated with Schistosoma-induced PH.

Macrophage Ontogeny, Phenotype, and Function in Ischemia Reperfusion-Induced Injury and Repair

AKI is characterized by a sudden, and usually reversible, decline in kidney function. In mice, ischemia-reperfusion injury (IRI) is commonly used to model the pathophysiologic features of clinical AKI. Macrophages are a unifying feature of IRI as they regulate both the initial injury response as well as the long-term outcome following resolution of injury. Initially, macrophages in the kidney take on a proinflammatory phenotype characterized by the production of inflammatory cytokines, such as CCL2 (monocyte chemoattractant protein 1), IL-6, IL-1 β , and TNF- α . Release of these proinflammatory cytokines leads to tissue damage. After resolution of the initial injury, macrophages take on a reparative role, aiding in tissue repair and restoration of kidney function. By contrast, failure to resolve the initial injury results in prolonged inflammatory macrophage accumulation and increased kidney damage, fibrosis, and the eventual development of CKD. Despite the extensive amount of literature that has ascribed these functions to M1/M2 macrophages, a recent paradigm shift in the macrophage field now defines macrophages on the basis of their ontological origin, namely monocyte-derived and tissue-resident macrophages. In this review, we focus on macrophage phenotype and function during IRI-induced injury, repair, and transition to CKD using both the classic (M1/M2) and novel (ontological origin) definition of kidney macrophages.

The roles of tissue-resident macrophages in sepsis-associated organ dysfunction

Sepsis, a syndrome caused by a dysregulated host response to infection and characterized by life-threatening organ dysfunction, particularly septic shock and sepsis-associated organ dysfunction (SAOD), is a medical emergency associated with high morbidity, high mortality, and long-term sequelae. Tissue-resident macrophages (TRMs) are a subpopulation of macrophages derived primarily from yolk sac progenitors and fetal liver during embryogenesis, located primarily in non-lymphoid tissues in adulthood, capable of local self-renewal independent of hematopoiesis, and developmentally and functionally restricted to the non-lymphoid organs in which they reside. TRMs are the first line of defense against life-threatening conditions such as sepsis, tumor growth, traumatic-associated organ injury, and surgical-associated injury. In the context of sepsis, TRMs can be considered as angels or demons involved in organ injury. Our proposal is that sepsis, septic shock, and SAOD can be attenuated by modulating TRMs in different organs. This review summarizes the pathophysiological mechanisms of TRMs in different organs or tissues involved in the development and progression of sepsis.

Metformin triggers a kidney GDF15-dependent area postrema axis to regulate food intake and body weight

Metformin, the most widely prescribed medication for obesity-associated type 2 diabetes (T2D), lowers plasma glucose levels, food intake, and body weight in rodents and humans, but the mechanistic site(s) of action remain elusive. Metformin increases plasma growth/differentiation factor 15 (GDF15) levels to regulate energy balance, while GDF15 administration activates GDNF family receptor α-like (GFRAL) that is highly expressed in the area postrema (AP) and the nucleus of the solitary tract (NTS) of the hindbrain to lower food intake and body weight. However, the tissue-specific contribution of plasma GDF15 levels after metformin treatment is still under debate. Here, we found that metformin increased plasma GDF15 levels in high-fat (HF) fed male rats through the upregulation of GDF15 synthesis in the kidney. Importantly, the kidney-specific knockdown of GDF15 expression as well as the AP-specific knockdown of GFRAL expression negated the ability of metformin to lower food intake and body weight gain. Taken together, we unveil the kidney as a target of metformin to regulate energy homeostasis through a kidney GDF15-dependent AP axis.

A kidney resident macrophage subset is a candidate biomarker for renal cystic disease in preclinical models

Although renal macrophages have been shown to contribute to cyst development in polycystic kidney disease (PKD) animal models, it remains unclear whether there is a specific macrophage subpopulation involved. Here, we analyzed changes in macrophage populations during renal maturation in association with cystogenesis rates in conditional Pkd2 mutant mice. We observed that CD206+ resident macrophages were minimal in a normal adult kidney but accumulated in cystic areas in adult-induced Pkd2 mutants. Using Cx3cr1 null mice, we reduced macrophage number, including CD206+ macrophages, and showed that this significantly reduced cyst severity in adult-induced Pkd2 mutant kidneys. We also found that the number of CD206+ resident macrophage-like cells increased in kidneys and in the urine from autosomal-dominant PKD (ADPKD) patients relative to the rate of renal functional decline. These data indicate a direct correlation between CD206+ resident macrophages and cyst formation, and reveal that the CD206+ resident macrophages in urine could serve as a biomarker for renal cystic disease activity in preclinical models and ADPKD patients. This article has an associated First Person interview with the first author of the paper.

Spontaneous Polycystic Kidneys with Chronic Renal Failure in an Aged House Musk Shrew (Suncus murinus)

Polycystic kidney disease is one of the most common inheritable renal diseases, characterized by the formation of multiple fluid-filled renal cysts. This disease is a progressive and unfortunately incurable condition. A case of polycystic kidney with chronic renal failure in house musk shrew (Suncus murinus) is described. At clinical presentation, a 16-month-old Suncus murinus showed weight loss and coarse fur. Regarding the biochemical profile, total protein concentrations increased, resulting in a declined albumin: globulin ratio. Blood urea nitrogen and creatinine concentrations were markedly elevated, indicating the end stage of chronic renal failure. Serum amyloid A levels increased and revealed inflammatory reaction during the cyst formation. Histopathologically, multiple cysts were lined by a single layer of epithelial cells or low cuboidal epithelium. The contents were homogenous eosinophilic materials (mucopolysaccharides or mucoproteins) and these cysts contained abundant macrophages. There were also regeneration and dilatation of renal tubes and interstitial fibrosis. The atrophic glomeruli and glomerular capsules were thickened and hyalinized by dense amorphous mucopolysaccharides. These histopathological findings suggested that the pathogenesis of polycystic kidney disease shared a common mechanistic feature across species.

Knockout of Bruton's tyrosine kinase in macrophages attenuates diabetic nephropathy in streptozotocin-induced mice

As a cytoplasmic tyrosine kinase in the Tec family, Bruton's tyrosine kinase (Btk) participates in various biological processes, including cell growth, differentiation, and apoptosis. Although recent studies have indicated that Btk is involved in pro-inflammatory cytokine production, the underlying impact of Btk on the development and pathogenesis of diabetic nephropathy (DN) has not been elucidated. The aim of this study was to determine whether Btk knockout (KO) could reduce inflammation and kidney injury in DN. First, diabetic mice models were established via an intraperitoneal injection of streptozotocin. Thereafter, the underlying mechanism was explored by comparing Btk ^flox/flox Lyz-Cre mice to wild-type (C57BL/6N) mice. Albuminuria was significantly reduced, and kidney injuries were attenuated in Btk conditional deletion diabetic mice. More importantly, these changes were demonstrated to be associated with decreased levels of pro-inflammatory cytokines owing to the downregulation of the MAPK and NF-κB signaling pathways. Collectively, these findings indicate that Btk plays a critical role in the regulation of kidney inflammation and provides a prospective therapeutic strategy for the treatment of DN.