Aging has small effects on initial ischemic acute kidney injury development despite changing intrarenal immunologic micromilieu in mice

Estrogen Protects against Renal Ischemia-Reperfusion Injury by Regulating Th17/Treg Cell Immune Balance

Inflammation is a critical mediator of renal ischemia-reperfusion (I/R) injury (IRI), and T lymphocytes exert a key role in the renal IRI-induced inflammation. Connexin 43 (Cx43) is related to the maintenance of T lymphocyte homeostasis. Various preclinical researches have reported that estrogen is a renoprotective agent based on its anti-inflammatory potential. The present research is aimed at studying the role of T lymphocytes activated by Cx43 in 17β-estradiol-mediated protection against renal IRI. Female rats were classified into six groups: control rats, I/R rats, ovariectomized rats, ovariectomized I/R rats, and ovariectomized rats treated with 17β-estradiol or gap27. Levels of serum creatinine (Scr) and blood urea nitrogen (BUN) and Paller scoring were dramatically increased in I/R rats, especially in ovariectomized rats. By contrast, these indicators were markedly decreased by administering estradiol or gap27. Immunofluorescence staining revealed that CD4⁺ T cells infiltrated kidney tissues in the early stage of IRI. In both peripheral blood and renal tissue, the proportion of CD3⁺CD4⁺ T cells and ratio of CD4⁺ to CD8⁺ were high in I/R rats, especially in ovariectomized rats. The proportion of CD3⁺CD8⁺ T cells was low in peripheral blood but high in renal tissues. Administration of estrogen or Gap27 reversed these effects. IL-17 levels in both serum and tissue homogenate were significantly increased in ovariectomized rats subjected to I/R but significantly decreased in estrogen or gap 27 treated rats. The opposite trend was observed for IL-10 levels. Correlation analysis demonstrated that IL-17 was correlated positively with BUN, Scr, and Paller scores, while IL-10 was negatively correlated with these indicators. Western blot showed that Cx43 expression was markedly increased in the peripheral blood T lymphocytes of I/R rats, especially ovariectomized rats. After intervention with estrogen and gap27, Cx43 expression was significantly downregulated. These findings indicate that Cx43 may participate in the regulation of Th17/Treg balance by estrogen against renal IRI.

Divergent regulation of lncRNA expression by ischemia in adult and aging mice

Elderly patients have increased susceptibility to acute kidney injury (AKI). Long noncoding RNAs (lncRNA) are key regulators of cellular processes, and have been implicated in both aging and AKI. Our aim was to study the effects of aging and ischemia-reperfusion injury (IRI) on the renal expression of lncRNAs. Adult and old (10- and 26-30-month-old) C57BL/6 N mice were subjected to unilateral IRI followed by 7 days of reperfusion. Renal expression of 90 lncRNAs and mRNA expression of injury, regeneration, and fibrosis markers was measured by qPCR in the injured and contralateral control kidneys. Tubular injury, regeneration, and fibrosis were assessed by histology. Urinary lipocalin-2 excretion was increased in old mice prior to IRI, but plasma urea was similar. In the control kidneys of old mice tubular cell necrosis and apoptosis, mRNA expression of kidney injury molecule-1, fibronectin-1, p16, and p21 was elevated. IRI increased plasma urea concentration only in old mice, but injury, regeneration, and fibrosis scores and their mRNA markers were similar in both age groups. AK082072 and Y lncRNAs were upregulated, while H19 and RepA transcript were downregulated in the control kidneys of old mice. IRI upregulated Miat, Igf2as, SNHG5, SNHG6, RNCR3, Malat1, Air, Linc1633, and Neat1 v1, while downregulated Linc1242. LncRNAs H19, AK082072, RepA transcript, and Six3os were influenced by both aging and IRI. Our results indicate that both aging and IRI alter renal lncRNA expression suggesting that lncRNAs have a versatile and complex role in aging and kidney injury. An Ingenuity Pathway Analysis highlighted that the most downregulated H19 may be linked to aging/senescence through p53.

Renal Aging Resembles a Continuum Between Normal and Diseased Kidneys That Potentiates Inflammatory Response to Injury

Renal aging is a natural process that can lead to structural changes and functional decline in the kidneys. These age-related changes are considered irreversible physiological processes, but resemble diseased kidneys. To enhance understanding of the molecular nature of renal aging, we first compared whole-kidney RNA sequencing between naturally aging mice (24-month-old) and adenine-induced nephropathy in young mice (2-month-old). Young mice (2-month-old) without intervention were used as the control group to investigate transcription alteration with aging or by adenine-enriched diet. Next, we compared the functional and structural renal consequences of aging and adenine-induced nephropathy between young (2-month-old) and old mice (18- to 22-month-old). C57BL/6 male mice were used in all experimental studies. Both aging kidneys and adenine-induced nephropathy showed similar transcriptional profiles characterized by upregulation in innate and adaptive immune system activation and inflammation, although these alterations were generally less significant in the aging kidneys. In contrast to aging kidneys, adenine-induced nephropathy showed prominent expression of the genes related to cytokines, T-cell activation, and fibrosis and decreased expression of the genes implicated in transporter activity and metabolism. The subclinical immunological micromilieu in aging kidneys potentially causes augmented kidney damage in response to injurious stimulus. When mice were fed with adenine-enriched diet, aging kidneys showed more extensive tubular injury and fibrosis with stronger inflammatory response than young kidneys. Taken together, our results suggest that renal aging may lie on a continuum between normal kidneys and diseased kidneys in the context of immune system upregulation that can worsen kidney damage upon injury.

Dietary Modification Alters the Intrarenal Immunologic Micromilieu and Susceptibility to Ischemic Acute Kidney Injury

The versatility of the intrarenal immunologic micromilieu through dietary modification and the subsequent effects on susceptibility to ischemic acute kidney injury (AKI) are unclear. We investigated the effects of high-salt (HS) or high-fat (HF) diet on intrarenal immunologic micromilieu and development of ischemic AKI using murine ischemic AKI and human kidney-2 (HK-2) cell hypoxia models. Four different diet regimens [control, HF, HS, and high-fat diet with high-salt (HF+HS)] were provided individually to groups of 9-week-old male C57BL/6 mice for 1 or 6 weeks. After a bilateral ischemia-reperfusion injury (BIRI) operation, mice were sacrificed on day 2 and renal injury was assessed with intrarenal leukocyte infiltration. Human kidney-2 cells were treated with NaCl or lipids. The HF diet increased body weight and total cholesterol, whereas the HF+HS did not. Although the HF or HS diet did not change total leukocyte infiltration at 6 weeks, the HF diet and HF+HS diet increased intrarenal CD8 T cells. Plasma cells increased in the HF and HS diet groups. The expression of proinflammatory cytokines including TNF-α, IFN-γ, MCP-1, and RANTES was increased by the HF or HS diet, and intrarenal VEGF decreased in the HS and HF+HS diet groups at 6 weeks. Deterioration of renal function following BIRI tended to be aggravated by the HF or HS diet. High NaCl concentration suppressed proliferation and enhanced expression of TLR-2 in hypoxic HK-2 cells. The HF or HS diet can enhance susceptibility to ischemic AKI by inducing proinflammatory changes to the intrarenal immunologic micromilieu.

The role of senescence of bone marrow cells in acute kidney injury

Background

The prevalence of acute kidney injury (AKI) in elderly patients has grown considerably. Age-associated changes in the immune system can be one of the critical factors determining AKI outcomes. This study aimed to investigate the role of senescence of bone marrow (BM)-derived cells in the development of AKI, focusing on the immune response.

Methods

Female 7-week-old C57BL/6 mice were irradiated and treated with BM cells from either 48-week-old or 8-week-old male mice. Ischemia-reperfusion injury (IRI) was induced, and their functional deterioration, histological tubular damage, and inflammatory responses were compared. For the in vitro study, lipopolysaccharide (LPS)-stimulated cytokine production by BM cells from old and young mice were examined.

Results

At 24 hours after IRI, there was no significant difference in the number of circulating immune cells between the mice transplanted with old or young BM cells. However, the mice with old BM cells showed less functional deterioration and histological tubular injury than those with young BM cells. Moreover, macrophage infiltration and renal cytokine interleukin (IL)-12 levels were lower in the mice with old BM cells at 24 hours post-IRI. Consistently, the in vitro study showed that LPS-induced production of cytokines interferon-γ, monocyte chemoattractant protein-1, and IL-10 was attenuated in cultured old BM cells, suggesting that age-related functional changes in these cells may lead to reduced inflammation in IRI.

Conclusion

Immunosenescence could affect the susceptibility and response to renal IRI. Further studies specifically addressing age-related alterations can help in the development of treatment strategies for elderly patients with AKI.

Moderate aging does not exacerbate cisplatin-induced kidney injury or fibrosis despite altered inflammatory cytokine expression and immune cell infiltration

Aging is a risk factor for certain forms of kidney injury due to normal physiological changes, but the role of aging in cisplatin-induced kidney injury is not well defined in humans or animal models of the disease. To improve on current knowledge in this field, we treated 8- and 40-wk-old FVB/n mice with one high dose of cisplatin as a model of acute kidney injury or with repeated low doses of cisplatin (7 mg/kg cisplatin once a week for 4 wk) as a clinically relevant model of chronic kidney disease to determine if aging exacerbates cisplatin-induced kidney injury. Levels of acute kidney injury were comparable in 8- and 40-wk-old mice. In 40-wk-old mice, fibrotic markers were elevated basally, but treatment with cisplatin did not exacerbate fibrosis. We concluded that this may be the result of a decreased inflammatory response in 40-wk-old cisplatin-treated mice compared with 8-wk-old mice. Despite a decreased inflammatory response, the level of immune cell infiltration was greater in 40-wk-old cisplatin-treated mice than 8-wk-old mice. Our data highlight the importance of examining age as a risk factor for cisplatin-induced kidney injury.

Immunopathogenesis of Acute Kidney Injury

Pathophysiologically, the classification of acute kidney injury (AKI) can be divided into three categories: (1) prerenal, (2) intrinsic, and (3) postrenal. Emerging evidence supports the involvement of renal tubular epithelial cells and the innate and adaptive arms of the immune system in the pathogenesis of intrinsic AKI. Pro-inflammatory damage-associated molecular patterns, pathogen-associated molecular patterns, hypoxia inducible factors, toll-like receptors, complement system, oxidative stress, adhesion molecules, cell death, resident renal dendritic cells, neutrophils, T and B lymphocytes, macrophages, natural killer T cells, cytokines, and secreted chemokines contribute to the immunopathogenesis of AKI. However, other immune cells and pathways such as M2 macrophages, regulatory T cells, progranulin, and autophagy exhibit anti-inflammatory properties and facilitate kidney tissue repair after AKI. Thus, therapies for AKI include agents such as anti-inflammatory (e.g., recombinant alkaline phosphatase), antioxidants (iron chelators), and apoptosis inhibitors. In preclinical toxicity studies, drug-induced kidney injury can be seen after exposure to a nephrotoxicant test article due to immune mechanisms and dysregulation of innate, and/or adaptive cellular immunity. The focus of this review will be on intrinsic AKI, as it relates to the immune and renal systems cross talks focusing on the cellular and pathophysiologic mechanisms of AKI.

Modelling physical resilience in ageing mice

Geroprotectors, a class of drugs targeting multiple deficits occurring with age, necessitate the development of new animal models to test their efficacy. The COST Action MouseAGE is a European network whose aim is to reach consensus on the translational path required for geroprotectors, interventions targeting the biology of ageing. In our previous work we identified frailty and loss of resilience as a potential target for geroprotectors. Frailty is the result of an accumulation of deficits, which occurs with age and reduces the ability to respond to adverse events (physical resilience). Modelling frailty and physical resilience in mice is challenging for many reasons. There is no consensus on the precise definition of frailty and resilience in patients or on how best to measure it. This makes it difficult to evaluate available mouse models. In addition, the characterization of those models is poor. Here we review potential models of physical resilience, focusing on those where there is some evidence that the administration of acute stressors requires integrative responses involving multiple tissues and where aged mice showed a delayed recovery or a worse outcome then young mice in response to the stressor. These models include sepsis, trauma, drug- and radiation exposure, kidney and brain ischemia, exposure to noise, heat and cold shock.