Tamoxifen for induction of Cre-recombination may confound fibrosis studies in female mice

Critical Role of histone deacetylase 3 in the regulation of kidney inflammation and fibrosis

Chronic kidney disease (CKD) is characterized by kidney inflammation and fibrosis. However, the precise mechanisms leading to kidney inflammation and fibrosis are poorly understood. Since histone deacetylase is involved in inflammation and fibrosis in other tissues, we examined the role of histone deacetylase 3 (HDAC3) in the regulation of inflammation and kidney fibrosis. HDAC3 is induced in the kidneys of animal models of CKD but mice with conditional HDAC3 deletion exhibit significantly reduced fibrosis in the kidneys compared with control mice. The expression of proinflammatory and profibrotic genes was significantly increased in the fibrotic kidneys of control mice, which was impaired in mice with HDAC3 deletion. Genetic deletion or pharmacological inhibition of HDAC3 reduced the expression of proinflammatory genes in cultured monocytes/macrophages. Mechanistically, HDAC3 deacetylates Lys122 of NF-κB p65 subunit turning on transcription. RGFP966, a selective HDAC3 inhibitor, reduced fibrosis in cells and in animal models by blocking NF-κB p65 binding to κB-containing DNA sequences. Thus, our study identified HDAC3 as a critical regulator of inflammation and fibrosis of the kidney through deacetylation of NF-κB unlocking its transcriptional activity. Hence, targeting HDAC3 could serve as a novel therapeutic strategy for CKD.

Kidney Injury by Unilateral Ureteral Obstruction in Mice Lacks Sex Differences

INTRODUCTION

Renal fibrosis is a critical event in the development and progression of chronic kidney disease (CKD), and it is considered the final common pathway for all types of CKD. The prevalence of CKD is higher in females; however, males have a greater prevalence of end-stage renal disease. In addition, low birth weight and low nephron number are associated with increased risk for CKD. This study examined the development and severity of unilateral ureter obstruction (UUO)-induced renal fibrosis in male and female wild-type (ROP +/+) and mutant (ROP Os/+) mice, a mouse model of low nephron number.

METHODS

Male and female ROP +/+ and ROP Os/+ mice were subjected to UUO, and kidney tissue was collected at the end of the 10-day experimental period. Kidney histological analysis and mRNA expression determined renal fibrosis, tubular injury, collagen deposition, extracellular matrix proteins, and immune cell infiltration.

RESULTS

Male and female UUO mice demonstrated marked renal injury, kidney fibrosis, and renal extracellular matrix production. Renal fibrosis and α-smooth muscle actin were increased to a similar degree in ROP +/+ and ROP Os/+ mice with UUO of either sex. There were also no sex differences in renal tubular cast formation or renal infiltration of macrophage in ROP +/+ and ROP Os/+ UUO mice. Interestingly, renal fibrosis and α-smooth muscle actin were 1.5-3-fold greater in UUO-ROP +/+ compared to UUO-ROP Os/+ mice. Renal inflammation phenotypes following UUO were also 30-45% greater in ROP +/+ compared to ROP Os/+ mice. Likewise, expression of extracellular matrix and renal fibrotic genes was greater in UUO-ROP +/+ mice compared to UUO-ROP Os/+ mice. In contrast to these findings, ROP Os/+ mice with UUO demonstrated glomerular hypertrophy with 50% greater glomerular tuft area compared to ROP +/+ with UUO. Glomerular hypertrophy was not sex-dependent in any of the genotypes of ROP mice. These findings provide evidence that low nephron number contributes to UUO-induced glomerular hypertrophy in ROP Os/+ mice but does not enhance renal fibrosis, inflammation, and renal tubular injury.

CONCLUSION

Taken together, we demonstrate that low nephron number contributes to enhanced glomerular hypertrophy but not kidney fibrosis and tubular injury. We also demonstrate that none of the changes caused by UUO was affected by sex in any of the ROP mice genotypes.

Krüppel-like Factor 5 Plays an Important Role in the Pathogenesis of Chronic Pancreatitis

Chronic pancreatitis results in the formation of pancreatic intraepithelial neoplasia (PanIN) and poses a risk of developing pancreatic cancer. Our previous study demonstrated that Krüppel-like factor 5 (KLF5) is necessary for forming acinar-to-ductal metaplasia (ADM) in acute pancreatitis. Here, we investigated the role of KLF5 in response to chronic injury in the pancreas. Human tissues originating from chronic pancreatitis patients showed increased levels of epithelial KLF5. An inducible genetic model combining the deletion of Klf5 and the activation of KrasG12D mutant expression in pancreatic acinar cells together with chemically induced chronic pancreatitis was used. The chronic injury resulted in increased levels of KLF5 in both control and KrasG12D mutant mice. Furthermore, it led to numerous ADM and PanIN lesions and extensive fibrosis in the KRAS mutant mice. In contrast, pancreata with Klf5 loss (with or without KrasG12D) failed to develop ADM, PanIN, or significant fibrosis. Furthermore, the deletion of Klf5 reduced the expression level of cytokines and fibrotic components such as Il1b, Il6, Tnf, Tgfb1, Timp1, and Mmp9. Notably, using ChIP-PCR, we showed that KLF5 binds directly to the promoters of Il1b, Il6, and Tgfb1 genes. In summary, the inactivation of Klf5 inhibits ADM and PanIN formation and the development of pancreatic fibrosis.

Confounding Effects of Tamoxifen: Cautionary and Practical Considerations for the Use of Tamoxifen-Inducible Mouse Models in Atherosclerosis Research-Brief Report

BACKGROUND

In recent years, fate-mapping lineage studies in mouse models have led to major advances in vascular biology by allowing investigators to track specific cell populations in vivo. One of the most frequently used lineage tracing approaches involves tamoxifen-inducible CreERT-LoxP systems. However, tamoxifen treatment can also promote effects independent of Cre recombinase activation, many of which have not been fully explored.

METHODS

To elucidate off-target effects of tamoxifen, male and female mice were either unmanipulated or injected with tamoxifen or corn oil. All mice received PCSK9 (proprotein convertase subtilisin/kexin type 9)-AAV (adeno-associated virus) injections and a modified Western diet to induce hypercholesterolemia. After 2 weeks, serum cholesterol and liver morphology were assessed. To determine the duration of any tamoxifen effects in long-term atherosclerosis experiments, mice received either 12 days of tamoxifen at baseline or 12 days plus 2 sets of 5-day tamoxifen boosters; all mice received PCSK9-AAV injections and a modified Western diet to induce hypercholesterolemia. After 24 weeks, serum cholesterol and aortic sinus plaque burden were measured.

RESULTS

After 2 weeks of atherogenic treatment, mice injected with tamoxifen demonstrated significantly reduced serum cholesterol levels compared with uninjected- or corn oil-treated mice. However, there were no differences in PCSK9-mediated knockdown of LDL (low-density lipoprotein) receptors between the groups. Additionally, tamoxifen-treated mice exhibited significantly increased hepatic lipid accumulation compared with the other groups. Finally, the effects of tamoxifen remained for at least 8 weeks after completion of injections, with mice demonstrating persistent decreased serum cholesterol and impaired atherosclerotic plaque formation.

CONCLUSIONS

In this study, we establish that tamoxifen administration results in decreased serum cholesterol, decreased plaque formation, and increased hepatic lipid accumulation. These alterations represent significant confounding variables in atherosclerosis research, and we urge future investigators to take these findings into consideration when planning and executing their own atherosclerosis experiments.

Reduction in Junctophilin 2 Expression in Cardiac Nodal Tissue Results in Intracellular Calcium-Driven Increase in Nodal Cell Automaticity

BACKGROUND

Spontaneously depolarizing nodal cells comprise the pacemaker of the heart. Intracellular calcium (Ca2+) plays a critical role in mediating nodal cell automaticity and understanding this so-called Ca2+ clock is critical to understanding nodal arrhythmias. We previously demonstrated a role for Jph2 (junctophilin 2) in regulating Ca2+-signaling through inhibition of RyR2 (ryanodine receptor 2) Ca2+ leak in cardiac myocytes; however, its role in pacemaker function and nodal arrhythmias remains unknown. We sought to determine whether nodal Jph2 expression silencing causes increased sinoatrial and atrioventricular nodal cell automaticity due to aberrant RyR2 Ca2+ leak.

METHODS

A tamoxifen-inducible, nodal tissue-specific, knockdown mouse of Jph2 was achieved using a Cre-recombinase-triggered short RNA hairpin directed against Jph2 (Hcn4:shJph2). In vivo cardiac rhythm was monitored by surface ECG, implantable cardiac telemetry, and intracardiac electrophysiology studies. Intracellular Ca2+ imaging was performed using confocal-based line scans of isolated nodal cells loaded with fluorescent Ca2+ reporter Cal-520. Whole cell patch clamp was conducted on isolated nodal cells to determine action potential kinetics and sodium-calcium exchanger function.

RESULTS

Hcn4:shJph2 mice demonstrated a 40% reduction in nodal Jph2 expression, resting sinus tachycardia, and impaired heart rate response to pharmacologic stress. In vivo intracardiac electrophysiology studies and ex vivo optical mapping demonstrated accelerated junctional rhythm originating from the atrioventricular node. Hcn4:shJph2 nodal cells demonstrated increased and irregular Ca2+ transient generation with increased Ca2+ spark frequency and Ca2+ leak from the sarcoplasmic reticulum. This was associated with increased nodal cell AP firing rate, faster diastolic repolarization rate, and reduced sodium-calcium exchanger activity during repolarized states compared to control. Phenome-wide association studies of the JPH2 locus identified an association with sinoatrial nodal disease and atrioventricular nodal block.

CONCLUSIONS

Nodal-specific Jph2 knockdown causes increased nodal automaticity through increased Ca2+ leak from intracellular stores. Dysregulated intracellular Ca2+ underlies nodal arrhythmogenesis in this mouse model.

Tamoxifen Ameliorates Cholestatic Liver Fibrosis in Mice: Upregulation of TGFβ and IL6 Is a Potential Protective Mechanism

The available treatments for cholestatic liver fibrosis are limited, and the disease often progresses to liver cirrhosis. Tamoxifen is a selective modulator of estrogen receptors, commonly used in breast cancer therapy. A recent in vitro study showed that tamoxifen deactivates hepatic stellate cells, suggesting its potential as an antifibrotic therapeutic, but its effects in vivo remain poorly investigated. In the present study, we show that tamoxifen protects against the cholestatic fibrosis induced by a diet supplemented with 0.025% 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). Mice fed with a DDC-supplemented diet for four weeks and treated with tamoxifen developed a significantly milder degree of liver fibrosis than vehicle-treated mice, as evidenced by a lower percentage of Sirius red-stained area (60.4% decrease in stained area in male and 42% decrease in female mice, p < 0.001 and p < 0.01, respectively) and by lower hydroxyproline content. The finding was further confirmed by qPCR analysis, which showed a lower expression of genes for Col1a1, Acta2, Sox9, Pdgf, and Krt19, indicating the inhibitory effect on hepatic stellate cells, collagen production, and biliary duct proliferation. The degree of protection was similar in male and female mice. Tamoxifen per se, injected into standard-diet-fed mice, increased the expression of genes for Il6 (p < 0.01 and p < 0.001 in male and female mice, respectively) and Tgfβ (p < 0.01 for both sexes), and had no adverse effects. We showed that tamoxifen sex-independently protects against cholestatic DDC-induced liver fibrosis. The increased expression of Il6 and Tgfβ seems to be a plausible protective mechanism that should be the primary focus of further research.

Transcriptomic Profiling in Mice With CB1 receptor Deletion in Primary Sensory Neurons Suggests New Analgesic Targets for Neuropathic Pain

Type 1 and type 2 cannabinoid receptors (CB1 and CB2, respectively) mediate cannabinoid-induced analgesia. Loss of endogenous CB1 is associated with hyperalgesia. However, the downstream targets affected by ablation of CB1 in primary sensory neurons remain unknown. In the present study, we hypothesized that conditional knockout of CB1 in primary sensory neurons (CB1cKO) alters downstream gene expression in the dorsal root ganglion (DRG) and that targeting these pathways alleviates neuropathic pain. We found that CB1cKO in primary sensory neurons induced by tamoxifen in adult Advillin-Cre:CB1-floxed mice showed persistent hyperalgesia. Transcriptome/RNA sequencing analysis of the DRG indicated that differentially expressed genes were enriched in energy regulation and complement and coagulation cascades at the early phase of CB1cKO, whereas pain regulation and nerve conduction pathways were affected at the late phase of CB1cKO. Chronic constriction injury in mice induced neuropathic pain and changed transcriptome expression in the DRG of CB1cKO mice, and differentially expressed genes were mainly associated with inflammatory and immune-related pathways. Nerve injury caused a much larger increase in CB2 expression in the DRG in CB1cKO than in wildtype mice. Interfering with downstream target genes of CB1, such as antagonizing CB2, inhibited activation of astrocytes, reduced neuroinflammation, and alleviated neuropathic pain. Our results demonstrate that CB1 in primary sensory neurons functions as an endogenous analgesic mediator. CB2 expression is regulated by CB1 and may be targeted for the treatment of neuropathic pain.

Sex and Tamoxifen confound murine experimental studies in cardiovascular tissue engineering

Tissue engineered vascular grafts hold promise for the creation of functional blood vessels from biodegradable scaffolds. Because the precise mechanisms regulating this process are still under investigation, inducible genetic mouse models are an important and widely used research tool. However, here we describe the importance of challenging the baseline assumption that tamoxifen is inert when used as a small molecule inducer in the context of cardiovascular tissue engineering. Employing a standard inferior vena cava vascular interposition graft model in C57BL/6 mice, we discovered differences in the immunologic response between control and tamoxifen-treated animals, including occlusion rate, macrophage infiltration and phenotype, the extent of foreign body giant cell development, and collagen deposition. Further, differences were noted between untreated males and females. Our findings demonstrate that the host-response to materials commonly used in cardiovascular tissue engineering is sex-specific and critically impacted by exposure to tamoxifen, necessitating careful model selection and interpretation of results.

Kidney pericyte hypoxia-inducible factor regulates erythropoiesis but not kidney fibrosis

Prolyl hydroxylase domain enzyme (PHD) inhibitors are effective in the treatment of chronic kidney disease (CKD)-associated anemia by stabilizing hypoxia inducible factor (HIF), thereby increasing erythropoietin and consequently erythropoiesis. However, concern for CKD progression needs to be addressed in clinical trials. Although pre-clinical studies showed an anti-inflammatory effect in kidney disease models, the effect of PHD inhibitors on kidney fibrosis was inconsistent probably because the effects of HIF are cell type and context dependent. The major kidney erythropoietin-producing cells are pericytes that produce erythropoietin through HIF-2α-dependent gene transcription. The concern for the impact of HIF in pericytes on kidney fibrosis arises from the fact that pericytes are the major precursor cells of myofibroblasts in CKD. Since cells expressing Gli1 fulfill the morphologic and anatomic criteria for pericytes, we induced Gli1⁺ cell-specific HIF stabilization or knockout to study the impact of HIF in pericytes on kidney pathology of mice with or without fibrotic injury induced by unilateral ureteral obstruction. Compared with the littermate controls, mice with pericyte-specific HIF stabilization due to von Hippel-Lindau protein or PHD2 knockout showed increased serum erythropoietin and polycythemia rather than a discernible difference in kidney fibrosis. Compared with Gli1⁺ pericytes sorted from littermate controls, Gli1⁺ pericytes sorted from PHD2 knockout mice showed increased erythropoietin gene expression rather than discernible changes in Col1a1 or Acta2 expression. Furthermore, pericyte-specific knockout of HIF-1α or HIF-2α did not affect kidney fibrosis. Thus, our study supports the absence of negative effects of PHD inhibitors on kidney fibrosis of mice despite HIF stabilization in pericytes.

Tamoxifen attenuates renal fibrosis in human kidney slices and rats subjected to unilateral ureteral obstruction

BACKGROUND AND PURPOSE

Renal fibrosis plays an important role in the development and progression of chronic kidney disease (CKD). Clinical studies have shown that CKD progresses differently in males and females, which may be related to circulating levels of sex hormones. In this study, we investigated the effect of tamoxifen (TAM), a selective estrogen receptor modulator (SERM), on renal fibrosis in male and female rats subjected to unilateral ureteral obstruction (UUO) and human precision-cut kidney slices (PCKS).

EXPERIMENTAL APPROACH

Female, ovariectomized female (OVX), and male rats were subjected to 7 days of UUO and treated with TAM by oral gavage. Moreover, we studied individual responses to TAM treatment in PCKS prepared from female and male patients. In all models, the expression of fibrosis markers was examined by western blot, qPCR, and immunohistochemistry.

KEY RESULTS

TAM decreased the expression of fibronectin, α-smooth muscle actin, and collagen-1 and -3 in female, OVX, and male rats. In addition, TAM mitigated TGF-β-induced fibrosis in human PCKS, irrespective of sex, yet interindividual differences in treatment response were observed.

CONCLUSION AND IMPLICATIONS

TAM ameliorates renal fibrosis in males and females, although we did observe sex differences in drug response. These findings warrant further research into the clinical applicability of TAM, or other SERMs, for the personalized treatment of renal disease.

Even a low dose of tamoxifen profoundly induces adipose tissue browning in female mice

BACKGROUND

Tamoxifen-inducible Cre/lox site-specific recombination technology has been widely used to generate conditional transgenic mice. As an estrogen receptor ligand, tamoxifen itself potentially affects energy metabolism, which may confound interpretation of data especially in metabolic studies. Considering sexual dimorphism, in this study, the effects of low-dose tamoxifen administration on energy metabolism, and browning of adipose tissues in female and male mice were investigated.

METHODS

Female and male C57/BL6 mice were injected with tamoxifen oil solution (i.p.) and then housed at both room temperature (23 ± 2 °C) and cold environment (6 ± 1 °C). Serum, brown and white adipose tissues were obtained, and the effects of tamoxifen administration on energy metabolism and the browning of adipose tissues were evaluated.

RESULTS

At 25 mg/kg body weight (BDW), tamoxifen administration for 3 alternative days decreased the percentage of inguinal and gonadal white adipose tissue weights in female mice accompanied by the up-regulation of thermogenesis in adipose tissues. In contrast, this dosage of tamoxifen did not induce noticeable changes in the energy metabolism and thermogenesis of adipose tissue in male mice under room temperature. Consistently, under cold stimulus, substantial browning of adipose tissues was observed in female mice injected with tamoxifen (50 mg/kg BDW, single injection) but not in male mice. Two-way ANOVA tests also demonstrated significant interactions between tamoxifen treatment and gender on the expression of thermogenic markers in adipose tissues.

CONCLUSION

Tamoxifen, even at a low dose, remarkably increases thermogenesis in adipose tissues of female mice; meanwhile, such a low dose could be used in male mice for inducing gene recombination without confounding the interpretation of data related to metabolism and thermogenesis of adipose tissues.

Sex differences in body composition but not neuromuscular function following long-term, doxycycline-induced reduction in circulating levels of myostatin in mice

Age-related declines in muscle function result from changes in muscle structure and contractile properties, as well as from neural adaptations. Blocking myostatin to drive muscle growth is one potential therapeutic approach. While the effects of myostatin depletion on muscle characteristics are well established, we have very little understanding of its effects on the neural system. Here we assess the effects of long-term, post-developmental myostatin reduction on electrophysiological motor unit characteristics and body composition in aging mice. We used male (N = 21) and female (N = 26) mice containing a tetracycline-inducible system to delete the myostatin gene in skeletal muscle. Starting at 12 months of age, half of the mice were administered doxycycline (tetracycline) through their chow for one year. During that time we measured food intake, body composition, and hindlimb electromyographic responses. Doxycycline-induced myostatin reduction had no effect on motor unit properties for either sex, though significant age-dependent declines in motor unit number occurred in all mice. However, treatment with doxycycline induced different changes in body composition between sexes. All female mice increased in total, lean and fat mass, but doxycycline-treated female mice experienced a significantly larger increase in lean mass than controls. All male mice also increased total and lean mass, but administration of doxycycline had no effect. Additionally, doxycycline-treated male mice maintained their fat mass at baseline levels, while the control group experienced a significant increase from baseline and compared to the doxycycline treated group. Our results show that long-term administration of doxycycline results in body composition adaptations that are distinctive between male and female mice, and that the effects of myostatin reduction are most pronounced during the first three months of treatment. We also report that age-related changes in motor unit number are not offset by reduced myostatin levels, despite increased lean mass exhibited by female mice.

Tamoxifen affects chronic pancreatitis-related fibrogenesis in an experimental mouse model: an effect beyond Cre recombination

Tamoxifen is very successfully used for the induction of Cre^ERT‐mediated genomic recombination in conditional mouse models. Recent studies, however, indicated that tamoxifen might also affect the fibrotic response in several disease models following administration, both in vitro and in vivo. In order to investigate a possible effect of tamoxifen on pancreatic fibrogenesis and to evaluate an optimal treatment scheme in an experimental pancreatitis mouse model, we administered tamoxifen by oral gavage to both male and female C57BL/6J mice and then waited for different periods of time before inducing chronic pancreatitis by cerulein. We observed a sex‐specific and time‐dependent effect of tamoxifen on the fibrotic response as measured by collagen deposition and the number of myofibroblasts and macrophages. The findings of in vitro studies, in which cerulein was administrated with or without 4‐hydroxytamoxifen to stimulate primary murine female and male pancreatic stellate cells, supported our in vivo observations. Real‐time PCR also indicated that this effect may be related to differences in ERα expression between female and male stellate cells. Our data demonstrate that tamoxifen administration has unignorable side effects, which affect the experimental outcome in a cerulein‐based model of chronic pancreatitis in mice. We suggest a 2‐week waiting period before cerulein administration to reduce side effects to a minimum for the described fibrosis model in female mice.

Expression of mutant Sftpc in murine alveolar epithelia drives spontaneous lung fibrosis

Epithelial cell dysfunction is postulated as an important component in the pathogenesis of idiopathic pulmonary fibrosis (IPF). Mutations in the surfactant protein C (SP-C) gene (SFTPC), an alveolar type II (AT2) cell-restricted protein, have been found in sporadic and familial IPF. To causally link these events, we developed a knockin mouse model capable of regulated expression of an IPF-associated isoleucine-to-threonine substitution at codon 73 (I73T) in Sftpc (SP-CI73T). Tamoxifen-treated SP-CI73T cohorts developed rapid increases in SftpcI73T mRNA and misprocessed proSP-CI73T protein accompanied by increased early mortality (days 7-14). This acute phase was marked by diffuse parenchymal lung injury, tissue infiltration by monocytes, polycellular alveolitis, and elevations in bronchoalveolar lavage and AT2 mRNA content of select inflammatory cytokines. Resolution of alveolitis (2-4 weeks), commensurate with a rise in TGF-β1, was followed by aberrant remodeling marked by collagen deposition, AT2 cell hyperplasia, α-smooth muscle actin-positive (α-SMA-positive) cells, and restrictive lung physiology. The translational relevance of the model was supported by detection of multiple IPF biomarkers previously reported in human cohorts. These data provide proof of principle that mutant SP-C expression in vivo causes spontaneous lung fibrosis, strengthening the role of AT2 cell dysfunction as a key upstream driver of IPF pathogenesis.

Evaluation of the safety and tolerability of tamoxifen for ischemia-incited renal injury in mice

Tamoxifen is used to activate tamoxifen-dependent Cre recombinase (CreER) to generate time- and tissue-specific genetically mutant mice. However, tamoxifen is also an active estrogen analogue that binds with higher affinity to estrogen receptors and exhibits anti-apoptosis, anti-inflammation, and antifibrotic properties. Renal ischemia reperfusion (I/R) injury is characterized by increased apoptosis and inflammation, so optimal utility of tamoxifen-inducible CreER genetic systems in I/R model is important. The purpose of this study was to optimize the tamoxifen dose and evaluate its safety and tolerability in the development of mouse I/R injury. Seven-week-old C57/B6 mice were subjected to moderate reversible unilateral I/R and then injected intraperitoneally daily for 5 days with tamoxifen at doses of 50, 100, or 200 mg/kg/day. Regardless of the time of sacrifice, at 5 day or 28 day after I/R injury, there were no differences in pathological damage, apoptosis, inflammation, or the extent of fibrosis between untreated and treated mice from the time point of acute kidney injury (AKI) to subsequently chronic kidney disease. Data above indicated that tamoxifen with a dose among 0 to 200 mg/kg/day was safe and tolerable for mice, without influencing I/R induced kidney injury in mice. The results suggest that tamoxifen-inducible CreER genetic systems can be safely used in the mouse I/R model.