Oncostatin M induced alpha1-antitrypsin (AAT) gene expression in Hep G2 cells is mediated by a 3' enhancer

Biodistribution and safety of a single rAAV3B-AAT vector for silencing and replacement of alpha-1 antitrypsin in Cynomolgus macaques

Alpha-1 antitrypsin deficiency (AATD) is characterized by both chronic lung disease due to loss of wild-type AAT (M-AAT) antiprotease function and liver disease due to toxicity from delayed secretion, polymerization, and aggregation of misfolded mutant AAT (Z-AAT). The ideal gene therapy for AATD should therefore comprise both endogenous Z-AAT suppression and M-AAT overexpression. We designed a dual-function rAAV3B (df-rAAV3B) construct, which was effective at transducing hepatocytes, resulting in a considerable decrease of Z-AAT levels and safe M-AAT augmentation in mice. We optimized df-rAAV3B and created two variants, AAV3B-E12 and AAV3B-G3, to simultaneously enhance the concentration of M-AAT in the bloodstream to therapeutic levels and silence endogenous AAT liver expression in cynomolgus monkeys. Our results demonstrate that AAV3b-WT, AAV3B-E12, and AAV3B-G3 were able to transduce the monkey livers and achieve high M-AAT serum levels efficiently and safely. In this nondeficient model, we did not find downregulation of endogenous AAT. However, the dual-function vector did serve as a potentially "liver-sparing" alternative for high-dose liver-mediated AAT gene replacement in the context of underlying liver disease.

Secretoglobin 3A2 protects lung from developing cigarette smoke-induced pulmonary emphysema

Secretoglobin (SCGB) 3A2 is a bioactive molecule exhibiting various functions such as improving allergic airway inflammation and pulmonary fibrosis and promoting bronchial branching and proliferation during lung development. To determine if and how SCGB3A2 is involved in chronic obstructive pulmonary disease (COPD), a multifactorial disease with both airway and emphysematous lesions, a COPD mouse model was created by exposing Scgb3a2-deficient (KO), Scgb3a2-lung-specific overexpressing (TG), and wild type (WT) mice to cigarette smoke (CS) for 6 months. The KO mice showed loss of lung structure under control condition, and CS exposure resulted in more expansion of airspace and destruction of alveolar wall than WT mouse lungs. In contrast, TG mouse lungs showed no significant changes after CS exposure. SCGB3A2 increased the expression and phosphorylation of signal transducers and activators of transcription (STAT)1 and STAT3, and the expression of α1-antitrypsin (A1AT) in mouse lung fibroblast-derived MLg cells and mouse lung epithelial-derived MLE-15 cells. In MLg cells, A1AT expression was decreased in Stat3-knockdown cells, and increased upon Stat3 overexpression. STAT3 formed a homodimer when cells were stimulated with SCGB3A2. Chromatin immunoprecipitation and reporter assays demonstrated that STAT3 binds to specific binding sites on the Serpina1a gene encoding A1AT and upregulates its transcription in lung tissues of mice. Furthermore, nuclear localization of phosphorylated STAT3 upon SCGB3A2 stimulation was detected by immunocytochemistry. These findings demonstrate that SCGB3A2 protects the lungs from the development of CS-induced emphysema by regulating A1AT expression through STAT3 signaling.

Alpha-1 antitrypsin governs alcohol-related liver disease in mice and humans

OBJECTIVE

Alcohol-related liver disease (ALD) is a global healthcare problem with limited treatment options. Alpha-1 antitrypsin (AAT, encoded by SERPINA1) shows potent anti-inflammatory activities in many preclinical and clinical trials. In our study, we aimed to explore the role of AAT in ALD.

DESIGN

An unselected cohort of 512 patients with cirrhosis was clinically characterised. Survival, clinical and biochemical parameters including AAT serum concentration were compared between patients with ALD and other aetiologies of liver disease. The role of AAT was evaluated in experimental ALD models.

RESULTS

Cirrhotic ALD patients with AAT serum concentrations less than 120 mg/dL had a significantly higher risk for death/liver transplantation as compared with patients with AAT serum concentrations higher than 120 mg/dL. Multivariate Cox regression analysis showed that low AAT serum concentration was a NaMELD-independent predictor of survival/transplantation. Ethanol-fed wild-type (wt) mice displayed a significant decline in hepatic AAT compared with pair-fed mice. Therefore, hAAT-Tg mice were ethanol-fed, and these mice displayed protection from liver injury associated with decreased steatosis, hepatic neutrophil infiltration and abated expression of proinflammatory cytokines. To test the therapeutic capability of AAT, ethanol-fed wt mice were treated with human AAT. Administration of AAT ameliorated hepatic injury, neutrophil infiltration and steatosis.

CONCLUSION

Cirrhotic ALD patients with AAT concentrations less than 120 mg/dL displayed an increased risk for death/liver transplantation. Both hAAT-Tg mice and AAT-treated wt animals showed protection from ethanol-induced liver injury. AAT could reflect a treatment option for human ALD, especially for alcoholic hepatitis.

SERPINA1 modulates expression of amyloidogenic transthyretin

Hereditary transthyretin amyloidosis (ATTR) is caused by amyloid deposition of misfolded transthyretin (TTR) in various tissues. Recently, reduction of circulating serum TTR, achieved via silencing oligonucleotides, was introduced as therapy of ATTR amyloidosis. We explored the impact of Serpin Family A Member 1 (SERPINA1) on TTR mRNA and protein expression. Oncostatin M (OSM) induced SERPINA1 in hepatoma cells and mice, while concomitantly TTR expression was significantly reduced. SERPINA1 knockdown resulted in specific elevated TTR expression in hepatoma cells; however other genes belonging to the group of acute phase proteins were unaffected. In mice, serum TTR was elevated after mSERPINA1 knockdown throughout antisense treatment. Following SERPINA1 knockdown, TTR deposition in several tissues, including dorsal root ganglia and intestine, was found to be increased, however numbers did not exceed significance levels. The data suggest that SERPINA1 is a co-factor of TTR expression. Our findings provide novel insight in the regulation of TTR and reveal a role of SERPINA1 in the pathogenesis of ATTR amyloidosis.

Liver organoids reproduce alpha-1 antitrypsin deficiency-related liver disease

BACKGROUND AND AIMS

Alpha-1 antitrypsin (AAT) is a product of SERPINA1 gene mainly expressed by hepatocytes. Clinically relevant mutations in the SERPINA1 gene, such as Z (Glu342Lys), results in an expression of misfolded AAT protein having high propensity to polymerize, accumulate in hepatocytes and thus to enhance a risk for hepatocyte damage and subsequent liver disease. So far, the relationship between the Z-AAT accumulation and liver cell damage remains not completely understood. We present three-dimensional organoid culture systems, as a novel tool for modeling Z-AAT-related liver diseases.

METHODS

We have established liver organoids from liver biopsies of patients with homozygous (ZZ) and heterozygous (MZ) deficiency and normal (MM) genotypes of AAT. The features of these organoid models were characterized by analyzing AAT protein secretion and intracellular aggregation in MZ and ZZ genotypes as well as SERPINA1 expression in differentiated cultures.

RESULTS

Transcriptional analysis of differentiated organoid cultures by RNA-Seq showed hepatocyte-specific gene expression profile. Genes, such as ALB, APOB, CYP3A4 and SERPINA1, were validated and confirmed through quantitative-PCR analysis. The organoids from MZ and ZZ cases showed intracellular aggregation and lower secretion of AAT protein, and lower expression of ALB and APOB, as typically seen in hepatocytes from Z-AAT deficiency patients. Furthermore, organoids responded to external stimulus. Treatment with oncostatin M, a well-known inducer of SERPINA1, increased expression of the full-length transcripts (AAT-1C) as well as the short transcript of AAT (AAT-ST1C4).

CONCLUSIONS

Liver organoid model recapitulates the key features of Z-AAT deficiency and provides a useful tool for disease modeling.

Serum Levels of Alpha1-antitrypsin and Their Relationship With COPD in the General Spanish Population

BACKGROUND

Low plasma level of alpha1-antitrypsin (AAT) is an established risk factor for early-onset chronic obstructive lung disease (COPD). However, less attention is given to the levels of AAT in the general population.

METHODS

This is a part of a multicentre, population-based study conducted at 11 sites throughout Spain. Plasma levels of AAT were available for 837 persons with a mean (SD) age of 58.05 (11.3) years: 328-smokers, 272-ex-smokers and 237 non-smokers. Out of 837, 303 (36.2%) had a diagnosis of COPD, 222 (26.5%) had respiratory symptoms but no COPD, and 312 (37.3%) were healthy controls.

RESULTS

In the whole cohort, the mean level of plasma AAT was 1.51 (0.47)g/L. Levels were higher in COPD patients [1.55 (0.45)g/L] and individuals with respiratory symptoms [1.57 (0.47)g/L] than in controls [1.43 (0.47)g/L], p<0.001, a finding which persisted after correction for age and CRP. Plasma AAT levels were negatively associated with FEV1/FVC ratio, after adjustment for age, sex, smoking status, CRP, TNFα, fibrinogen and albumin. The risk for COPD was significantly associated with higher AAT levels in univariate and multivariate models, with odds ratios of 1.8 and 1.5, respectively. In the univariate and multivariate models smoking status, gender, and CRP levels were also associated with COPD probability, demonstrating that they act independently.

CONCLUSION

Increased circulating levels of AAT, similarly to CRP and other markers of systemic inflammation, is an important feature of COPD. Our results highlight a complex interrelationship between levels of AAT and health of respiratory system.

The molecular immunology of human susceptibility to fungal diseases: lessons from single gene defects of immunity

INTRODUCTION

Fungal diseases are a threat to human health. Therapies targeting the fungus continue to lead to disappointing results. Strategies targeting the host response represent unexplored opportunities for innovative treatments. To do so rationally requires the identification and neat delineation of critical mechanistic pathways that underpin human antifungal immunity. The study of humans with single-gene defects of the immune system, i.e. inborn errors of immunity (IEIs), provides a foundation for these paradigms. Areas covered: A systematic literature search in PubMed, Scopus, and abstracts of international congresses was performed to review the history of genetic resistance/susceptibility to fungi and identify IEIs associated with fungal diseases. Immunologic mechanisms from relevant IEIs were integrated with current definitions and understandings of mycoses to establish a framework to map out critical immunobiological pathways of human antifungal immunity. Expert opinion: Specific immune responses non-redundantly govern susceptibility to their corresponding mycoses. Defining these molecular pathways will guide the development of host-directed immunotherapies that precisely target distinct fungal diseases. These findings will pave the way for novel strategies in the treatment of these devastating infections.

Snail and serpinA1 promote tumor progression and predict prognosis in colorectal cancer

The role of Snail and serpin peptidase inhibitor clade A member 1 (serpinA1) in tumorigenesis has been previously identified. However, the exact role and mechanism of these proteins in progression of colorectal cancer (CRC) are controversial. In this study, we investigated the role of Snail and serpinA1 in colorectal cancer (CRC) and examined the mechanisms through which these proteins mediate CRC progression. Immunohistochemical analysis of 528 samples from patients with CRC showed that elevated expression of Snail or serpinA1 was correlated with advanced stage, lymph node metastasis, and poor prognosis. Moreover, we detected a correlation between Snail and serpinA1 expression. Functional studies performed using the CRC cell lines DLD-1 and SW-480 showed that overexpression of Snail or serpinA1 significantly increased CRC cell invasion and migration. Conversely, knockdown of Snail or serpinA1 expression suppressed CRC cell invasion and migration. ChIP analysis revealed that Snail regulated serpinA1 by binding to its promoter. In addition, fibronectin mediated Snail and serpinA1 signaling was involved in CRC cell invasion and migration. Taken together, our data showed that Snail and serpinA1 promoted CRC progression through fibronectin. These findings suggested that Snail and serpinA1 were novel prognostic biomarkers and candidate therapeutic targets in CRC.

Leptin Resistance: A Possible Interface Between Obesity and Pulmonary-Related Disorders

CONTEXT

Under normal physiological conditions, leptin regulates body weight by creating a balance between food intake and energy expenditure. However, in obesity, serum leptin levels increase and become defective to retain energy balance.

EVIDENCE ACQUISITION

Elevated serum leptin levels are regarded as an established marker of obesity. It is also reported that obese asthmatic patients have maximum serum leptin levels compared to other groups such as non-obese asthmatics, and normal obese and non obese subjects without asthma. In addition to having an appetite suppressing effect, leptin also regulates certain acute-phase protein expressions including α-1 antitrypsin (A1AT) in the liver.

RESULTS

A1AT is a protease inhibitor that counterbalances the activity of the neutrophil elastase (NE) enzyme. A1AT reductions in obese-leptin resistant subjects lead to increased NE activity. The overactivity of NE degrades lung tissue proteins, which may lead to pulmonary disorders including asthma.

CONCLUSIONS

On the basis of prior studies, it could be hypothesized that, in obese asthmatic patients, the highest degree of leptin failure/resistance might lead to the creation of an imbalance between NE and its inhibitor A1AT. To ascertain this, large scale prospective studies are warranted to assess the comparative serum leptin and A1AT levels and NE activity in asthmatic non-obese and obese patients, simultaneously. Such studies might help to devise novel interventional therapies for the treatment of pulmonary-related problems including asthma, chronic obstructive pulmonary disorder (COPD), and other lung defects in susceptible obese subjects in the future.

Plasma α1-antitrypsin: a neglected predictor of angiographic severity in patients with stable angina pectoris

Background:

As an acute phase protein, α1-antitrypsin (AAT) has been extensively studied in acute coronary syndrome, but it is unclear whether a relationship exists between AAT and stable angina pectoris (SAP). The purpose of the present study was to investigate the association between AAT plasma levels and SAP.

Methods:

Overall, 103 SAP patients diagnosed by coronary angiography and clinical manifestations and 118 control subjects matched for age and gender were enrolled in this case-control study. Plasma levels of AAT, high-sensitivity C-reactive protein (hsCRP), lipid profiles and other clinical parameters were assayed for all participants. The severity of coronary lesions was evaluated based on the Gensini score (GS) assessed by coronary angiography.

Results:

Positively correlated with the GS (r = 0.564, P < 0.001), the plasma AAT level in the SAP group was significantly higher than that in the control group (142.08 ± 19.61 mg/dl vs. 125.50 ± 19.67 mg/dl, P < 0.001). The plasma AAT level was an independent predictor for both SAP (odds ratio [OR] = 1.037, 95% confidence interval [CI]: 1.020–1.054, P < 0.001) and a high GS (OR = 1.087, 95% CI: 1.051–1.124, P < 0.001) in a multivariate logistic regression model. In the receiver operating characteristic curve analysis, plasma AAT level was found to have a larger area under the curve (AUC) for predicting a high GS (AUC = 0.858, 95% CI: 0.788–0.929, P < 0.001) than that of hsCRP (AUC = 0.665, 95% CI: 0.557–0.773, P = 0.006; Z = 2.9363, P < 0.001), with an optimal cut-off value of 137.85 mg/dl (sensitivity: 94.3%, specificity: 68.2%).

Conclusions:

Plasma AAT levels correlate with both the presence and severity of coronary stenosis in patients with SAP, suggesting that it could be a potential predictive marker of severe stenosis in SAP patients.

Risk loci for chronic obstructive pulmonary disease: a genome-wide association study and meta-analysis

BACKGROUND

The genetic risk factors for susceptibility to chronic obstructive pulmonary disease (COPD) are still largely unknown. Additional genetic variants are likely to be identified by genome-wide association studies in larger cohorts or specific subgroups. We sought to identify risk loci for moderate to severe and severe COPD with data from several cohort studies.

METHODS

We combined genome-wide association analysis data from participants in the COPDGene study (non-Hispanic white and African-American ethnic origin) and the ECLIPSE, NETT/NAS, and Norway GenKOLS studies (self-described white ethnic origin). We did analyses comparing control individuals with individuals with moderate to severe COPD and with a subset of individuals with severe COPD. Single nucleotide polymorphisms yielding a p value of less than 5 × 10(-7) in the meta-analysis at loci not previously described were genotyped in individuals from the family-based ICGN study. We combined results in a joint meta-analysis (threshold for significance p<5 × 10(-8)).

FINDINGS

Analysis of 6633 individuals with moderate to severe COPD and 5704 control individuals confirmed association at three known loci: CHRNA3 (p=6·38 × 10(-14)), FAM13A (p=1·12 × 10(-14)), and HHIP (p=1·57 × 10(-12)). We also showed significant evidence of association at a novel locus near RIN3 (p=5·25 × 10(-9)). In the overall meta-analysis (ie, including data from 2859 ICGN participants), the association with RIN3 remained significant (p=5·4 × 10(-9)). 3497 individuals were included in our analysis of severe COPD. The effect estimates for the loci near HHIP and CHRNA3 were significantly stronger in severe disease than in moderate to severe disease (p<0·01). We also identified associations at two additional loci: MMP12 (overall joint meta-analysis p=2·6 × 10(-9)) and TGFB2 (overall joint meta-analysis p=8·3 × 10(-9)).

INTERPRETATION

We have confirmed associations with COPD at three known loci and identified three new genome-wide significant associations. Genetic variants other than in α-1 antitrypsin increase the risk of COPD.

FUNDING

US National Heart, Lung, and Blood Institute; the Alpha-1 Foundation; the COPD Foundation through contributions from AstraZeneca, Boehringer Ingelheim, Novartis, and Sepracor; GlaxoSmithKline; Centers for Medicare and Medicaid Services; Agency for Healthcare Research and Quality; and US Department of Veterans Affairs.

Secretomic analysis identifies alpha-1 antitrypsin (A1AT) as a required protein in cancer cell migration, invasion, and pericellular fibronectin assembly for facilitating lung colonization of lung adenocarcinoma cells

Metastasis is a major obstacle that must be overcome for the successful treatment of lung cancer. Proteins secreted by cancer cells may facilitate the progression of metastasis, particularly within the phases of migration and invasion. To discover metastasis-promoting secretory proteins within cancer cells, we used the label-free quantitative proteomics approach and compared the secretomes from the lung adenocarcinoma cell lines CL1-0 and CL1-5, which exhibit low and high metastatic properties, respectively. By employing quantitative analyses, we identified 660 proteins, 68 of which were considered to be expressed at different levels between the two cell lines. High levels of A1AT were secreted by CL1-5, and the roles of A1AT in the influence of lung adenocarcinoma metastasis were investigated. Molecular and pathological confirmation demonstrated that altered expression of A1AT correlates with the metastatic potential of lung adenocarcinoma. The migration and invasion properties of CL1-5 cells were significantly diminished by reducing the expression and secretion of their A1AT proteins. Conversely, the migration and invasion properties of CL1-0 cells were significantly increased through the overexpression and secretion of A1AT proteins. Furthermore, the assembly levels of the metastasis-promoting pericellular fibronectin (FN1), which facilitates colonization of lung capillary endothelia by adhering to the cell surface receptor dipeptidyl peptidase IV (DPP IV), were higher on the surfaces of suspended CL1-5 cells than on those of the CL1-0 cells. This discovery reflects previous findings in breast cancer. In line with this finding, FN1 assembly and the lung colonization of suspended CL1-5 cells were inhibited when endogenous A1AT protein was knocked down using siRNA. The major thrust of this study is to demonstrate the effects of coupling the label-free proteomics strategy with the secretomes of cancer cells that differentially exhibit invasive and metastatic properties. This provides a new opportunity for the effective identification of metastasis-associated proteins that are secreted by cancer cells and promote experimental metastasis.

Retinal Mueller Glial Cells Trigger the Hallmark Inflammatory Process in Autoimmune Uveitis

Spontaneous equine recurrent uveitis (ERU) is an incurable autoimmune disease affecting the eye. Although retinal-autoantigen specific T-helper 1 cells have been demonstrated to trigger disease progression and relapses, the molecular processes leading to retinal degeneration and consequent blindness remain unknown. To elucidate such processes, we studied changes in the total retinal proteome of ERU-diseased horses compared to healthy controls. Severe changes in the retinal proteome were found for several markers for blood-retinal barrier breakdown and whose emergence depended upon disease severity. Additionally, uveitic changes in the retina were accompanied by upregulation of aldose 1-epimerase, selenium-binding protein 1, alpha crystallin A chain, phosphatase 2A inhibitor (SET), and glial fibrillary acidic protein (GFAP), the latter indicating an involvement of retinal Mueller glial cells (RMG) in disease process. To confirm this, we screened for additional RMG-specific markers and could demonstrate that, in uveitic retinas, RMG concomitantly upregulate vimentin and GFAP and downregulate glutamine synthetase. These expression patterns suggest for an activated state of RMG, which further downregulate the expression of pigment epithelium-derived factor (PEDF) and begin expressing interferon-gamma, a pro-inflammatory cytokine typical for T-helper 1 cells. We thus propose that RMG may play a fatal role in uveitic disease progression by directly triggering inflammatory processes through the expression and secretion of interferon-gamma.

Human amniotic epithelial cells possess hepatocyte-like characteristics and functions

Hepatocyte transplantation is expected to become a novel method for treatment of liver disease. However, many questions remain regarding this approach, especially concerning donor cells. To evaluate whether human amniotic epithelial cells can be used as a cell source for hepatocyte transplantation, hepatic gene expression and functions of human amniotic epithelial cells were analyzed. Reverse transcription-polymerase chain reaction analysis demonstrated that human amniotic epithelial cells expressed albumin, alpha(1)-antitrypsin, and other hepatocyte-related genes. Cultivated human amniotic epithelial cells demonstrated albumin production, glycogen storage, and albumin secretion consistent with the hepatocyte gene expression profile. In organ culture, the amnion secreted 30-fold larger amounts of albumin than human amniotic epithelial cells in monolayer culture. Moreover, in organ culture the amnion also secreted alpha(1)-antitrypsin. Following transplantation into mice, the amnion survived and secreted albumin. These observations suggest that transplantation of human amniotic epithelial cells and/or amnion could be novel therapeutic strategy for treatment of hepatic diseases, including alpha(1)-antitrypsin deficiency.

Effect of invertebrate serine proteinase inhibitors on carrageenan-induced pleural exudation and bradykinin release

The carrageenan model of pleurisy is described as temporal plasma exudation (1-5 h) with extensive neutrophil infiltration and release of proteinases into the pleural cavity. The aim of this work was to study the effects of serine proteinase inhibitors on the inflammatory process induced by administration of carrageenan to the rat pleural cavity and on release of kinins in pleural exudate. Pleurisy was induced by injecting carrageenan and serine proteinase inhibitors simultaneously into the pleural cavity. The proteinase inhibitors used were: aprotinin, a plasma kallikrein inhibitor; recombinant leech derived tryptase inhibitor-2PL (LDTI-2PL), a plasmin inhibitor; Boophilus microplus trypsin inhibitors (BmTIs); trypsin; plasma kallikrein; plasmin and neutrophil elastase inhibitors; and a synthetic neutrophil elastase inhibitor (EIsynt). Administration of carrageenan with LDTI-2PL and BmTIs induced a marked increase in exudation (143% and 201%) and leukocyte migration (288% and 408%), respectively, when compared to the control group. Pleural exudate from LDTI-2PL and BmTIs plus carrageenan-treated rats showed a significant increase in plasma kallikrein-like activity, measured by chromogenic substrate hydrolysis. The specific inhibition of enzymatic activity with aprotinin confirmed that 50% of S2302 hydrolysis was produced by plasma kallikrein-like enzymes. Kinin release was increased by 97% and 103% in exudates from LDTI-2PL and BmTIs plus carrageenan-treated rats, respectively. Considering that the plasmin inhibitors LDTI-2PL and BmTIs increased exudation, leukocyte migration and bradykinin release, our results suggest an anti-inflammatory role for plasmin in the pleurisy model.

The genomic response of the mouse kidney to low-phosphate diet is altered in X-linked hypophosphatemia

The mechanism for the renal adaptation to low-phosphate diets is not well understood. Whether the Hyp mutation of the Phex gene blocks this adaptation is also not clear. To gain further insight into this, 5-wk-old normal and Hyp mice were fed a control (1.0% P) or low-phosphate diet (0.03% P) for 3-5 days. Renal RNA was hybridized to Affymetrix U74Av2 microarrays (5 arrays/group). Of the 5,719 detectable genes on each array, 290 responded significantly (P < 0.01) to low-phosphate diet in normal mice. This was reduced significantly (P < 0.001) to 7 in the Hyp mice. This suggested that the adaptations of the normal kidney to a low-phosphate environment were blocked by the Hyp mutation. The Npt2 phosphate transporter, vitamin D 1alpha- and 24-hydroxylases, and calbindins D9K and D28K responded in the expected fashion. Genes with significant (P < 0.05) diet-by-genotype interaction were analyzed by GenMAPP and MAPPFinder. This revealed a cluster of differentially expressed genes associated with microtubule-based processes. Most alpha- and beta-tubulins and most kinesins had responses to low-phosphate diet in normal mice which were abolished or reversed in Hyp mice. In summary, renal adaptation to low-phosphate diet involved changes in the mRNA expression of specific genes. Disruption of these responses in Hyp mice may contribute to their abnormal phosphate homeostasis.