Midkine is involved in kidney development and in its regulation by retinoids

Advances in the Management of Primary Membranous Nephropathy and Rituximab-Refractory Membranous Nephropathy

Primary membranous nephropathy (pMN) is an auto-immune disease characterized by auto-antibodies targeting podocyte antigens resulting in activation of complement and damage to the glomerular basement membrane. pMN is the most common cause of nephrotic syndrome in adults without diabetes. Despite a very heterogeneous course of the disease, the treatment of pMN has for many years been based on uniform management of all patients regardless of the severity of the disease. The identification of prognostic markers has radically changed the vision of pMN and allowed KDIGO guidelines to evolve in 2021 towards a more personalized management based on the assessment of the risk of progressive loss of kidney function. The recognition of pMN as an antibody-mediated autoimmune disease has rationalized the use immunosuppressive drugs such as rituximab. Rituximab is now a first line immunosuppressive therapy for patients with pMN with proven safety and efficacy achieving remission in 60-80% of patients. For the remaining 20-40% of patients, several mechanisms may explain rituximab resistance: (i) decreased rituximab bioavailability; (ii) immunization against rituximab; and (iii) chronic glomerular damage. The treatment of patients with rituximab-refractory pMN remains controversial and challenging. In this review, we provide an overview of recent advances in the management of pMN (according to the KDIGO 2021 guidelines), in the understanding of the pathophysiology of rituximab resistance, and in the management of rituximab-refractory pMN. We propose a treatment decision aid based on immunomonitoring to identify failures related to underdosing or immunization against rituximab to overcome treatment resistance.

Midkine: The Who, What, Where, and When of a Promising Neurotrophic Therapy for Perinatal Brain Injury

Midkine (MK) is a small secreted heparin-binding protein highly expressed during embryonic/fetal development which, through interactions with multiple cell surface receptors promotes growth through effects on cell proliferation, migration, and differentiation. MK is upregulated in the adult central nervous system (CNS) after multiple types of experimental injury and has neuroprotective and neuroregenerative properties. The potential for MK as a therapy for developmental brain injury is largely unknown. This review discusses what is known of MK's expression and actions in the developing brain, areas for future research, and the potential for using MK as a therapeutic agent to ameliorate the effects of brain damage caused by insults such as birth-related hypoxia and inflammation.

Single-cell transcriptomics reveals gene expression dynamics of human fetal kidney development

The current understanding of mammalian kidney development is largely based on mouse models. Recent landmark studies revealed pervasive differences in renal embryogenesis between mouse and human. The scarcity of detailed gene expression data in humans therefore hampers a thorough understanding of human kidney development and the possible developmental origin of kidney diseases. In this paper, we present a single-cell transcriptomics study of the human fetal kidney. We identified 22 cell types and a host of marker genes. Comparison of samples from different developmental ages revealed continuous gene expression changes in podocytes. To demonstrate the usefulness of our data set, we explored the heterogeneity of the nephrogenic niche, localized podocyte precursors, and confirmed disease-associated marker genes. With close to 18,000 renal cells from five different developmental ages, this study provides a rich resource for the elucidation of human kidney development, easily accessible through an interactive web application.

Diagnostic and Prognostic Value of Talin-1 and Midkine as Tumor Markers in Hepatocellular Carcinoma in Egyptian Patients

Background:

Hepatocellular carcinoma (HCC) is a main cause of cancer death all over the world. Treatment and outcome of HCC based on its early diagnosis. This study was conducted to estimate the role of talin-1 and midkine in combination with total antioxidant capacity (TAC) as tumor markers in HCC patients.

Methods:

Serum levels of talin-1 and midkine were measured in 90 Egyptian subjects including 44 patients with HCC, 31patients with cirrhosis and 15 healthy controls using enzyme-linked immunosorbent assay (ELISA) technique. While a colorimetric method was used for measurement of TAC.

Results:

Serum talin-1 in HCC patients was significantly lower than that in patients with cirrhosis (P<0.001) and normal control (P<0.001). In addition, increased invasion and metastasis correlated with reduced talin-1 level. Serum midkine in HCC patients was significantly higher compared to cirrhotic patients (P<0.001) and normal control (P<0.001). Midkine at a cut off value of 1683 pg/ml showed a sensitivity of (81.82%) and specificity of (83.87%). While alpha-fetoprotein (AFP) at a cut off value of 200 ng/ml had a sensitivity of (52.27%), while specificity was (96.77%). Midkine was positive in 80.9% of HCC patients with negative AFP. Serum TAC was significantly decreased in HCC patients when compared with control group (P<0.001).

Conclusion:

Talin-1 may be implicated in the carcinogenesis and metastasis of HCC and can be used as a useful tumor marker for HCC. Midkine may be a potential diagnostic marker for HCC and may be used in addition to AFP to increase the sensitivity of HCC detection.

Urine and serum midkine levels in an Australian chronic kidney disease clinic population: an observational study

BACKGROUND AND OBJECTIVES

The cytokine midkine (MK) is pathologically implicated in progressive chronic kidney disease (CKD) and its systemic consequences and has potential as both a biomarker and therapeutic target. To date, there are no published data on MK levels in patients with different stages of CKD. This study aims to quantify MK levels in patients with CKD and to identify any correlation with CKD stage, cause, progression, comorbid disease or prescribed medication.

METHODS

In this observational, single-centre study, demographic data were collected, and serum and urine assayed from 197 patients with CKD and 19 healthy volunteers in an outpatient setting.

RESULTS

The median serum and urine MK level in volunteers was 754 pg/mL (IQR: 554-1025) and 239 pg/mL (IQR: 154-568), respectively. Compared with serum MK in stage 1 CKD (660 pg/mL, IQR: 417-893), serum MK increased in stage 3 (1878 pg/mL, IQR: 1188-2756; p<0.001), 4 (2768 pg/mL, IQR: 2065-4735; p<0.001) and 5 (4816 pg/mL, IQ: 37477807; p<0.001). Urine MK levels increased from stage 1 CKD (343 pg/mL, IQR: 147-437) to stage 3 (1007 pg/mL, IQR: 465-2766; p=0.07), 4 (2961 pg/mL, IQR: 1368-5686; p=0.005) and 5 (6722 pg/mL, IQR: 3796-10 060; p=0.001). Fractional MK excretion (FeMK) increased from stage 1 CKD (0.159, IQR: 0.145-0.299) to stage 3 (1.024, IQR: 0.451-1.886, p=0.047), 4 (3.39, IQR: 2.10-5.82, p=0.004) and 5 (11.95, IQR: 5.36-24.41, p<0.001). When adjusted for estimated glomerular filtration rate, neither serum nor urine MK correlated with primary CKD diagnosis or CKD progression (small sample). There was a positive correlation between protein:creatinine ratio and FeMK (p=0.003). Angiotensin blockade (adjusted for proteinuria) was associated with lower urine MK (p=0.018) and FeMK (p=0.025).

CONCLUSION

MK levels sequentially rise with CKD stage beyond stage 2, and our data support existing animal evidence for an MK/renin angiotensin-system/proteinuria relationship. To what extent this is related to renal clearance versus pathology, or the consequences of chronically elevated MK levels requires further exploration.

Cellular heterogeneity in the ureteric progenitor niche and distinct profiles of branching morphogenesis in organ development

Branching morphogenesis creates arborized epithelial networks. In the mammalian kidney, an epithelial progenitor pool at ureteric branch tips (UBTs) creates the urine-transporting collecting system. Using region-specific mouse reporter strains, we performed an RNA-seq screen, identifying tip- and stalk-enriched gene sets in the developing collecting duct system. Detailed in situ hybridization studies of tip-enriched predictions identified UBT-enriched gene sets conserved between the mouse and human kidney. Comparative spatial analysis of their UBT niche expression highlighted distinct patterns of gene expression revealing novel molecular heterogeneity within the UBT progenitor population. To identify kidney-specific and shared programs of branching morphogenesis, comparative expression studies on the developing mouse lung were combined with in silico analysis of the developing mouse salivary gland. These studies highlight a shared gene set with multi-organ tip enrichment and a gene set specific to UBTs. This comprehensive analysis extends our current understanding of the ureteric branch tip niche.

Circulating midkine in children with Henoch-Schönlein purpura: Clinical implications

BACKGROUND

Midkine (MK) is a heparin-binding growth factor, which behaves like a cytokine, involved in various cellular processes such as cellular proliferation, differentiation, survival, adhesion, and migration. Studies provided evidence for a role of MK in acute and chronic inflammatory processes. The association between midkine and Henoch-Schönlein purpura (HSP) has not yet been explored. The aim of our study was to investigate the potential role of midkine in children with HSP.

METHODS

A total of 152 cases consisting of 92 children with HSP and 60 age- and sex-matched healthy control children were enrolled in this prospective study. Circulating midkine, IL-2, IL-4, IL-6, IL-10, TNF, IFN-γ, and IL-17A was measured in all of the 92 patients and 60 healthy controls. Midkine diagnostic value was evaluated by receiver operating characteristic (ROC) analysis.

RESULTS

Renal involvement occurred in 36 of the 92 patients. Circulating midkine level was elevated in children with HSPN than those of patients without renal involvement and of the controls (326.58 (266.58-459.25) pg/ml versus 280.72 (233.67-384.36) pg/ml and 217.3 (198.98-243.65) pg/ml, respectively; P<0.05). Midkine positively correlated with IL-4, IL-6, IL17A, IgA and IgE. The threshold MK concentration of HSPN was 295.58pg/ml, with the sensitivity and specificity of 80.6% and 88.3%, respectively. The area under the receiver operating characteristic (ROC) curve (AUCROC) of MK was 0.902.

CONCLUSIONS

MK seems to be involved in the development of HSP. Measurement of serum levels of MK is helpful in confirming the diagnosis of HSP and predicting HSPN.

Inhibition of terminal complement: a novel therapeutic approach for the treatment of systemic lupus erythematosus

The importance of the complement system in the pathophysiology of systemic lupus erythematosus (SLE) is clear although individual complement components play very different roles in the disease process. Early complement proteins are critical in the clearance of immune complexes and apoptotic bodies, and their absencepredisposesindividualsto SLE. Conversely, activationof terminalcomplement is associated with exacerbations of disease and damage to tissues and organs, particularly in lupus nephritis. Monoclonal antibodies that specifically inhibit terminal complement activation while preserving the critical functions of the early complement cascade have now been developed. These antibodies target the C5 complement protein, blocking its cleavage and the subsequent generation of potent proinflammatory molecules. Anti-C5 therapeutics have recently been investigated in an animal model of SLE and in a Phase I single dose study in humans. The results of these studiesand the multiple roles of complement in SLE are discussed.

Midkine in nephrogenesis, hypertension and kidney diseases

Midkine (MK; K; gene abbreviation, Mdk: mus musculus, MDK: homo sapiens) is a multifunctional heparin-binding growth factor that regulates cell growth, survival and migration as well as anti-apoptotic activity in nephrogenesis and development. Proximal tubular epithelial cells are the main sites of MK expression in the kidneys. The pathophysiological roles of MK are diverse, ranging from the development of acute kidney injury (AKI) to the progression of chronic kidney disease, often accompanied by hypertension, renal ischaemia and diabetic nephropathy. The obvious hypertension that develops in Mdk(+/+) mouse models of renal ablation compared with Mdk(-/-) mice eventually leads to progressive renal failure, such as glomerular sclerosis and tubulointerstitial damage associated with elevated plasma angiotensin (Ang) II levels. MK is also induced in the lung endothelium by oxidative stress and subsequently up-regulated by ACE, which hydrolyzes Ang II to induce further oxidative stress, thus accelerating MK generation; this leads to a vicious cycle of positive feedback in the MK-Ang II pathway. Kidney-lung interactions involving positive feedback between the renin-angiotensin system and MK might partly account for the pathogenesis of hypertension and kidney damage. MK is also involved in the pathogenesis of AKI and diabetic nephropathy through the recruitment of inflammatory cells. In contrast, MK plays a protective role against crescentic glomerulonephritis, by down-regulating plasminogen activator inhibitor-1. These diverse actions of MK might open up new avenues for targeted approaches to treating hypertension and various renal diseases.

LINKED ARTICLES

This article is part of a themed section on Midkine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-4.

Developmental origins of chronic renal disease: an integrative hypothesis

Cardiovascular diseases are one of the leading causes of mortality. Hypertension (HT) is one of the principal risk factors associated with death. Chronic kidney disease (CKD), which is probably underestimated, increases the risk and the severity of adverse cardiovascular events. It is now recognized that low birth weight is a risk factor for these diseases, and this relationship is amplified by a rapid catch-up growth or overfeeding during infancy or childhood. The pathophysiological and molecular mechanisms involved in the “early programming” of CKD are multiple and partially understood. It has been proposed that the developmental programming of arterial hypertension and chronic kidney disease is related to a reduced nephron endowment. However, this mechanism is still discussed. This review discusses the complex relationship between birth weight and nephron endowment and how early growth and nutrition influence long term HT and CKD. We hypothesize that fetal environment reduces moderately the nephron number which appears insufficient by itself to induce long term diseases. Reduced nephron number constitutes a “factor of vulnerability” when additional factors, in particular a rapid postnatal growth or overfeeding, promote the early onset of diseases through a complex combination of various pathophysiological pathways.

Low ambient o(2) enhances ureteric bud branching in vitro

Hypoxia exists widely in developing embryos where it may regulate blood vessel formation. VEGF and FGF2 produced in developing renal primordia (metanephroi) stimulate microvessel formation from embryonic thoracic aorta cultured under hypoxic conditions (HC) relative to room air (RA). The aim of the present study was to provide insight into the participation of hypoxia in a process that occurs concomitant with metanephros vascularization in vivo, ureteric bud (UB) branching. To this end, the arborization of the UB and growth of metanephroi were measured in metanephroi grown in serum-free organ culture for two days under RA or HC. When metanephroi were cultured under HC the arborization of UB was stimulated relative to RA. In the presence of anti-VEGF neutralizing antibody (alphamVEGF), or anti-FGF2 neutralizing antibody (alphahFGF2) UB branching was inhibited under both RA and HC. When both alphamVEGF and alphahFGF2 were added, the inhibition was enhanced. Addition of exogenous VEGF or FGF2 to cultures stimulated UB branching under RA and HC and addition of both stimulated it further. These findings provide evidence for roles of hypoxia and metanephric VEGF and FGF2, as regulators not only for vascularization but also for UB bud branching during renal organogenesis.

Midkine promotes selective expansion of the nephrogenic mesenchyme during kidney organogenesis

During kidney development, the growth and development of the stromal and nephrogenic mesenchyme cell populations and the ureteric bud epithelium is tightly coupled through intricate reciprocal signaling mechanisms between these three tissue compartments. Midkine, a target gene activated by retinoid signaling in the metanephros, encodes a secreted polypeptide with mitogenic and anti-apoptotic activities in a wide variety of cell types. Using immmunohistochemical methods we demonstrated that Midkine is found in the uninduced mesenchyme at the earliest stages of metanephric kidney development and only subsequently concentrated in the ureteric bud epithelium and basement membrane. The biological effects of purified recombinant Midkine were analyzed in metanephric organ culture experiments carried out in serum-free defined media. These studies revealed that Midkine selectively promoted the overgrowth of the Pax-2 and N-CAM positive nephrogenic mesenchymal cells, failed to stimulate expansion of the stromal compartment and suppressed branching morphogenesis of the ureteric bud. Midkine suppressed apoptosis and stimulated cellular proliferation of the nephrogenic mesenchymal cells, and was capable of maintaining the viability of isolated mesenchymes cultured in the absence of the ureteric bud. These results suggest that Midkine may regulate the balance of epithelial and stromal progenitor cell populations of the metanephric mesenchyme during renal organogenesis.

Adverse consequences of accelerated neonatal growth: cardiovascular and renal issues

Epidemiological and experimental studies show that the risk of cardiovascular and metabolic diseases at adulthood is inversely related to the weight at birth. Although with less evidence, low birth weight has been suggested to increase the risk of chronic kidney disease (CKD). It is well established that the developmental programming of arterial hypertension and of renal disease involves in particular renal factors, especially nephron endowment, which is reduced in low birth weight and maternal diabetes situations. Experimental studies, especially in rodents, have demonstrated the long-term influence of postnatal nutrition and/or postnatal growth on cardiovascular, metabolic and renal functions, while human data are scarce on this issue. Vascular and renal diseases appear to have a "multihits" origin, with reduced nephron number the initial hit and rapid postnatal growth the second hit. This review addresses the current understanding of the role of the kidney, both as a mechanism and as a target, in the developmental origins of adult disease theory, with a particular focus on the long-term effects of postnatal growth and nutrition.

Endogenous retinoic acid activity in principal cells and intercalated cells of mouse collecting duct system

BACKGROUND

Retinoic acid is the bioactive derivative of vitamin A, which plays an indispensible role in kidney development by activating retinoic acid receptors. Although the location, concentration and roles of endogenous retinoic acid in post-natal kidneys are poorly defined, there is accumulating evidence linking post-natal vitamin A deficiency to impaired renal concentrating and acidifying capacity associated with increased susceptibility to urolithiasis, renal inflammation and scarring. The aim of this study is to examine the presence and the detailed localization of endogenous retinoic acid activity in neonatal, young and adult mouse kidneys, to establish a fundamental ground for further research into potential target genes, as well as physiological and pathophysiological roles of endogenous retinoic acid in the post-natal kidneys.

METHODOLOGY/PRINCIPAL FINDINGS

RARE-hsp68-lacZ transgenic mice were employed as a reporter for endogenous retinoic acid activity that was determined by X-gal assay and immunostaining of the reporter gene product, β-galactosidase. Double immunostaining was performed for β-galactosidase and markers of kidney tubules to localize retinoic acid activity. Distinct pattern of retinoic acid activity was observed in kidneys, which is higher in neonatal and 1- to 3-week-old mice than that in 5- and 8-week-old mice. The activity was present specifically in the principal cells and the intercalated cells of the collecting duct system in all age groups, but was absent from the glomeruli, proximal tubules, thin limbs of Henle's loop and distal tubules.

CONCLUSIONS/SIGNIFICANCE

Endogenous retinoic acid activity exists in principal cells and intercalated cells of the mouse collecting duct system after birth and persists into adulthood. This observation provides novel insights into potential roles for endogenous retinoic acid beyond nephrogenesis and warrants further studies to investigate target genes and functions of endogenous retinoic acid in the kidney after birth, particularly in the collecting duct system.

Midkine: a novel prognostic biomarker for cancer

Since diagnosis at an early stage still remains a key issue for modern oncology and is crucial for successful cancer therapy, development of sensitive, specific, and non-invasive tumor markers, especially, in serum, is urgently needed. Midkine (MK), a plasma secreted protein, was initially identified in embryonal carcinoma cells at early stages of retinoic acid-induced differentiation. Multiple studies have reported that MK plays important roles in tumor progression, and is highly expressed in various malignant tumors. Because increased serum MK concentrations also have been reported in patients with various tumors, serum MK may have the potential to become a very useful tumor marker. Here, we review and discuss the possibility and usefulness of MK as a novel tumor marker.

Midkine in plasma as a novel breast cancer marker

Midkine, a heparin-binding growth factor, is up-regulated in many types of cancer. The aim of this study was to measure plasma midkine levels in patients with breast cancer and to assess its clinical significance. We examined plasma midkine levels in 95 healthy volunteers, 11 patients with ductal carcinoma in situ (DCIS), 111 patients with primary invasive breast cancer without distant metastasis (PIBC), and 25 patients with distant metastatic breast cancer (MBC), using an automatic immunoasssay analyzer (TOSOH AIA system). In PIBC, we studied the correlation between plasma midkine levels and clinicopathological factors. Immunoreactive midkine was detectable in the plasma of healthy volunteers, and a cut-off level of 750 pg/mL was established. In breast cancer patients, plasma midkine levels were increased above normal values. These elevated levels of midkine were seen in one (9.1%) of 11 patients with DCIS, 36 (32.4%) of 111 patients with PIBC, and 16 (64.0%) of 25 patients with MBC. Increased levels of midkine were correlated with menopausal status (P = 0.0497) and nuclear grade (P = 0.0343) in PIBC. Cancer detection rates based on midkine levels were higher than those based on three conventional markers including CA15-3 (P < 0.0001), CEA (P = 0.0077), and NCCST-439 (P < 0.0001). Detection rates of breast cancer using a combination of two conventional tumor markers (CA15-3/CEA, CA15-3/NCCST-439, or CEA/NCCST-439) with midkine is significantly higher than those using combination of three conventional tumor markers. Midkine may be a useful novel tumor marker for detection of breast cancer, superior to conventional tumor markers.

Monoclonal antibodies for podocytopathies: rationale and clinical responses

The podocytopathies, including minimal-change nephropathy, focal segmental glomerulosclerosis, collapsing glomerulopathy, and diffuse mesangial sclerosis, involve diverse types of injury to podocytes. These injuries can have genetic causes, or can be caused by viral infection, mechanical stress, medication or-probably-immunologic injury. Several lines of evidence-including the immunosuppressive effects of standard therapies-suggest a role for immunologic injury in some cases, but the precise pathologic mechanisms are far from clear. Despite this uncertainty, newly available biologic therapies that target immune cells and cytokines have been used to treat a number of patients with different podocytopathies. Of these therapies, the greatest experience has been gained with rituximab. The data on all such therapies remain too fragmentary to provide firm conclusions, but further clinical research with such agents might help to define pathogenetic pathways and could potentially contribute to new therapies.

Present and future drug treatments for chronic kidney diseases: evolving targets in renoprotection

At present, there are no specific cures for most of the acquired chronic kidney diseases, and renal transplantation is limited by organ shortage, therefore present efforts are concentrated on the prevention of progression of renal diseases. There is robust experimental and clinical evidence that progression of chronic nephropathies is multifactorial; however, intraglomerular haemodynamic changes and proteinuria play a key role in this process. With a focus on renoprotection, we first examine more established therapies--such as those that modulate the renin-angiotensin-aldosterone system--that can be used for the treatment of proteinuric renal diseases. We then discuss examples of novel drugs and biologics that might be used to target the inflammatory and profibrotic process, and glomerular injury, highlighting results from recent clinical trials.

Discovery and development of the complement inhibitor eculizumab for the treatment of paroxysmal nocturnal hemoglobinuria

The complement system provides critical immunoprotective and immunoregulatory functions but uncontrolled complement activation can lead to severe pathology. In the rare hemolytic disease paroxysmal nocturnal hemoglobinuria (PNH), somatic mutations result in a deficiency of glycosylphosphatidylinositol-linked surface proteins, including the terminal complement inhibitor CD59, on hematopoietic stem cells. In a dysfunctional bone marrow background, these mutated progenitor blood cells expand and populate the periphery. Deficiency of CD59 on PNH red blood cells results in chronic complement-mediated intravascular hemolysis, a process central to the morbidity and mortality of PNH. A recently developed, humanized monoclonal antibody directed against complement component C5, eculizumab (Soliris; Alexion Pharmaceuticals Inc., Cheshire, CT, USA), blocks the proinflammatory and cytolytic effects of terminal complement activation. The recent approval of eculizumab as a first-in-class complement inhibitor for the treatment of PNH validates the concept of complement inhibition as an effective therapy and provides rationale for investigation of other indications in which complement plays a role.

Female infertility in mice deficient in midkine and pleiotrophin, which form a distinct family of growth factors

Midkine and pleiotrophin form a family of growth factors. Mice deficient in one of the genes show few abnormalities on reproduction and development. To understand their roles in these processes, we produced mice deficient in both genes; the double deficient mice were born in only one third the number expected by Mendelian segregation and 4 weeks after birth weighed about half as much as wild-type mice. Most of the female double deficient mice were infertile. In these mice, the numbers of mature follicles and of ova at ovulation were reduced compared to numbers in wild-type mice. Both midkine and pleiotrophin were expressed in the follicular epithelium and granulosa cells of the ovary. The expression of these factors in the uterus was dramatically altered during the estrous cycle. The diestrus and proestrus periods were long and the estrus period was short in the double deficient mice, indicating the role of the factors in the estrous cycle. Furthermore, vaginal abnormality was found in about half of the double deficient mice. These abnormalities in combination resulted in female infertility. Therefore, midkine and pleiotrophin, together with their signaling receptors, play important roles in the female reproductive system.

Kidney-specific upregulation of vitamin D3 target genes in ClC-5 KO mice

Mutations in ClC-5 cause Dent's disease, a disorder associated with low molecular weight proteinuria, hyperphosphaturia, and kidney stones. ClC-5 is a Cl(-)/H(+)-exchanger predominantly expressed in the kidney, where it facilitates the acidification of proximal tubular endosomes. The reduction in proximal tubular endocytosis resulting from a lack of ClC-5 raises the luminal concentration of filtered proteins and peptides like parathyroid hormone (PTH). The increase in PTH may explain the hyperphosphaturia observed in Dent's disease. Expression profiling, quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR), and hormone measurements were used to investigate whether the disruption of ClC-5 affects other signalling pathways. Although the upregulation of 25(OH)(2)-vitamin D(3) 1alpha-hydroxylase and downregulation of vitamin D(3) 24-hydroxylase suggested an increased formation of 1,25(OH)(2)-vitamin D(3), the concentration of this active metabolite was reduced in the serum of ClC-5 knockout (KO) mice. However, target genes of 1,25(OH)(2)-vitamin D(3) were upregulated in KO kidneys. Expression analysis of intestine and bone revealed that the upregulation of 1,25(OH)(2)-vitamin D(3) target genes was kidney intrinsic and not systemic. In spite of reduced serum levels of 1,25(OH)(2)-vitamin D(3) in ClC-5 KO mice, 1,25(OH)(2)-vitamin D(3) is increased in later nephron segments as a consequence of impaired proximal tubular endocytosis. This leads to a kidney-specific stimulation of 1,25(OH)(2)-vitamin D(3) target genes that may contribute to the pathogenesis of Dent's disease. The activation of genes in distal nephron segments by hormones that are normally endocytosed in the proximal tubule may extend to other pathways like those activated by retinoic acid.

Identification of differentially expressed genes between fetal and adult mouse kidney: candidate gene in kidney development

BACKGROUND

The kidney development involves a wide variety of developmental processes requiring a lot of genes expressed in a sequential manner. The aim of the present study is to identify new genes involved in these processes.

METHODS

To obtain a view of the mouse embryonic kidney transcriptome we used the SADE method, which allows large-scale quantitative gene expression measurements.

RESULTS

7,689 tags were sequenced from our library. Among the 4,507 unique transcripts yielded, 64% correspond to known genes, 22% ESTs, 12% unidentified genes. 472 genes were differentially expressed as compared to published adult kidney library. Among these, we identified several candidate genes and focused on a particular one: thymosin beta4 (Tbeta4), an actin-sequestering protein more highly expressed in fetal kidney. First we studied the in vivo expression patterns of Tbeta4 transcript during kidney development. Tbeta4 increases throughout the kidney development and remains high during active nephrogenesis. Moreover, the spatial distribution of Tbeta4 mRNA was analysed and reveals that during active nephrogenesis (i.e., 18 dpc) Tbeta4 is localised in differentiating glomeruli. In adult kidney, Tbeta4 remains expressed in podocytes and collecting ducts.

CONCLUSION

Our results provide the first demonstration of Tbeta4 production in vivo by embryonic kidney and further show that Tbeta4 is implicated in kidney organogenesis.

Global analysis of RAR-responsive genes in the Xenopus neurula using cDNA microarrays

Retinoid signaling is important for patterning the vertebrate hindbrain and midaxial regions. We recently showed that signaling through retinoic acid receptors (RARs) is essential for anteroposterior patterning along the entire body axis. To further investigate the mechanisms through which RARs act, we used microarray analysis to investigate the effects of modulating RAR activity on target gene expression. We identified 334 up-regulated genes (92% of which were validated), including known RA-responsive genes, known genes that have never been proposed as RA targets and many hypothetical and unidentified genes (n = 166). Sixty-seven validated down-regulated genes were identified, including known RA-responsive genes and anterior marker genes. The expression patterns of selected up-regulated genes (n = 45) were examined at neurula stages using whole-mount in situ hybridization. We found that most of these genes were expressed in the neural tube and many were expressed in anterior tissues such as neural crest, brain, eye anlagen, and cement gland. Some were expressed in tissues such as notochord, somites, pronephros, and blood islands, where retinoic acid (RA) plays established roles in organogenesis. Members of this set of newly identified RAR target genes are likely to play important roles in neural patterning and organogenesis under the control of RAR signaling pathways, and their further characterization will expand our understanding of RA signaling during development.

Long-term circulatory and renal consequences of intrauterine growth restriction

Intrauterine growth restriction (IUGR) and probably also early postnatal altered nutrition in very-low-birthweight babies may, in the long term, be followed by the various disorders that are included in the metabolic syndrome. This discovery has raised a new paradigm about the background to cardiovascular disease, arterial hypertension, obesity, type 2 diabetes and dyslipidaemic disorders that play a prominent role in shortening human life. In this review article, present knowledge about the background to renal dysfunction as seen in IUGR is summarized. The way in which arterial hypertension and cardiovascular dysfunction may be programmed in IUGR is also speculated.

CONCLUSION

During the last decade, knowledge of the long-term consequences of IUGR has increased at a very rapid rate. At present, it is most important not only to develop efficient methods of preventing and diagnosing IUGR, but to work out follow-up and treatment programmes for the control of the disorders which may follow this condition. Proper postnatal feeding and infant growth may be essential for long-term outcome.

Midkine, a newly discovered regulator of the renin–angiotensin pathway in mouse aorta: Significance of the pleiotrophin/midkine developmental gene family in angiotensin II signaling

We previously demonstrated that pleiotrophin (PTN the protein, Ptn the gene) highly regulates the levels of expression of the genes encoding the proteins of the renin-angiotensin pathway in mouse aorta. We now demonstrate that the levels of expression of these same genes are significantly regulated in mouse aorta by the PTN family member midkine (MK the protein, Mk the gene); a 3-fold increase in expression of renin, an 82-fold increase in angiotensinogen, a 6-fold decrease in the angiotensin converting enzyme, and a 6.5-fold increase in the angiotensin II type 1 and a 9-fold increase in the angiotensin II type 2 receptor mRNAs were found in Mk-/- mouse aorta in comparison with the wild type (WT, +/+). The results in Mk-/- mice are remarkably similar to those previously reported in Ptn-/- mouse aorta, with the single exception of that the levels of the angiotensinogen gene expression in Ptn-/- mice are equal to those in WT+/+ mouse aorta, and thus, in contrast to Mk gene expression unaffected by levels of Ptn gene expression. The data indicate that MK and PTN share striking but not complete functional redundancy. These data support potentially high levels importance of MK and the MK/PTN developmental gene family in downstream signals initiated by angiotensin II either in development or in the many pathological conditions in which MK expression levels are increased, such as atherosclerosis and many human neoplasms that acquire constitutive endogenous Mk gene expression by mutation during tumor progression and potentially provide a target through the renin-angiotensin pathway to treat advanced malignancies.

Lack of the growth factor midkine enhances survival against cisplatin-induced renal damage

Although cisplatin acts directly on proximal tubule epithelial cells and causes cell death, little is known regarding the biological significance of its secondary effects, such as inflammation. The growth factor midkine is highly expressed in the proximal tubule and exerts ambivalent activities as to cisplatin nephrotoxicity, ie, anti-apoptotic and chemotactic ones. Here we report that midkine-deficient mice show a significantly higher survival rate than wild-type mice. The levels of blood urea nitrogen and tubular degeneration and apoptosis were higher in wild-type mice despite the anti-apoptotic activity of midkine. We found that recruitment of neutrophils was more enhanced in wild-type mice, this being consistent with the chemotactic activity of midkine. Midkine expression in wild-type mice persisted for 24 hours, and then dramatically decreased. Preadministration of midkine anti-sense oligodeoxyribonucleotide to wild-type mice suppressed midkine expression, and consequently neutrophil infiltration. It is of note that neutrophil infiltration, apoptosis, and elevation of blood urea nitrogen became conspicuous sequentially, namely 1, 2, and 3 days after cisplatin administration, respectively. These findings suggest that early molecular events involving midkine induce inflammatory response and their circuits eventually enhance the death of the proximal tubule epithelial cells. The results indicate the crucial role of inflammation in cisplatin-induced renal damage, and provide a candidate molecular target for its prevention.

Retinoids in nephrology: Promises and pitfalls

BACKGROUND

Retinoids, a family of vitamin A metabolites or analogs, play an important role in regulating cell proliferation, differentiation, and apoptosis.

METHODS

The biological importance of retinoids in the kidney and the potential of retinoids in the treatment of renal diseases are reviewed.

RESULTS

Vitamin A deficiency and mutations of retinoid nuclear receptors cause abnormalities in fetal kidneys, which might predispose to adult diseases such as hypertension. Further, the therapeutic value of retinoids in animal models of kidney diseases, such as lupus nephritis, puromycin aminonucleoside nephrosis, anti-glomerular basement membrane nephritis, mesangioproliferative nephritis, and acute renal allograft rejection has been unveiled recently. Retinoids target mesangial cells, podocytes, tubular epithelial cells, interstitial fibroblasts, as well as lymphocytes and macrophages. The anti-inflammation, anti-coagulation effects, and the proliferation- and immunity-modulating actions of retinoids, have been widely appreciated. Our recent in vitro data revealed a direct antifibrotic effect and a cytoprotective effect of retinoids in various renal cell types. In animal studies, the adverse effects of retinoids are generally minimal; however, the clinical use of retinoids in other diseases points to some major side effects. In addition, in vitro, retinoids can induce lipid accumulation in smooth muscle cells and macrophages and increase expression of some proinflammatory molecules, indicating that their clinical toxicity profile in the setting of renal diseases needs to be better understood.

CONCLUSION

Retinoids not only are important in renal development, but also show promise as a new generation of renal medication and deserve to be tested in clinical trials to clarify their full potential.

Pathogenesis of perinatal programming

PURPOSE OF REVIEW

In recent years, there has been an increase in research designed to delineate the underlying causes of perinatal programming. Starting with epidemiological observations that birth weight was inversely associated with cardiovascular disease, a variety of studies both in humans and in experimental models have begun to demonstrate how the perinatal milieu can subtly alter vasculogenesis and nephrogenesis. Additionally, rates of prenatal and postnatal growth each appear to contribute to future vascular, renal and metabolic function. The purpose of this review is to discuss recent reports that have begun to elucidate factors that initiate perinatal programming as it affects renal disease and cardiovascular disease in later life.

RECENT FINDINGS

Nephrogenesis per se is affected by changes in maternal nutrition and health, and recent data more specifically linking these changes with renal function and hypertension are presented. Additionally, renal functional changes in later life may be influenced by changes in renal tubular transporters noted early when maternal nutrition is compromised. Various hormonal systems affected by maternal nutrition in utero may effect subsequent changes in renal function via subtle alterations in renal function and structure initiated during nephrogenesis.

SUMMARY

Current research is beginning to clarify certain aspects of perinatal programming and indicates that broad educational programmes might ultimately lessen both perinatal risks and long-term outcomes by encouraging therapeutic interventions in at-risk persons.

A catalogue of gene expression in the developing kidney

BACKGROUND

Although many genes with important function in kidney morphogenesis have been described, it is clear that many more remain to be discovered. Microarrays allow a more global analysis of the genetic basis of kidney organogenesis.

METHODS

In this study, Affymetrix U74Av2 microarrays, with over 12,000 genes represented, were used in conjunction with robust target microamplification techniques to define the gene expression profiles of the developing mouse kidney.

RESULTS

Microdissected murine ureteric bud and metanephric mesenchyme as well as total kidneys at embryonic day E11.5, E12.5, E13.5, E16.5, and adult were examined. This work identified, for example, 3847 genes expressed in the E12.5 kidney. Stringent comparison of the E12.5 versus adult recognized 428 genes with significantly elevated expression in the embryonic kidney. These genes fell into several functional categories, including transcription factor, growth factor, signal transduction, cell cycle, and others. In contrast, surprisingly few differences were found in the gene expression profiles of the ureteric bud and metanephric mesenchyme, with many of the differences clearly associated with the more epithelial character of the bud. In situ hybridizations were used to confirm and extend microarray-predicted expression patterns in the developing kidney. For three genes, Cdrap, Tgfbi, and Col15a1, we observed strikingly similar expression in the developing kidneys and lungs, which both undergo branching morphogenesis.

CONCLUSION

The results provide a gene discovery function, identifying large numbers of genes not previously associated with kidney development. This study extends developing kidney microarray analysis to the powerful genetic system of the mouse and establishes a baseline for future examination of the many available mutants. This work creates a catalogue of the gene expression states of the developing mouse kidney and its microdissected subcomponents.

Midkine and pleiotrophin in neural development and cancer

The midkine (MK) family consists of only two members, namely heparin-binding growth factors MK and pleiotrophin (PTN). During embryogenesis, MK is highly expressed in the mid-gestational period, whereas PTN expression reaches the maximum level around birth. Both proteins are localized in the radial glial processes of the embryonic brain, along which neural stem cells migrate and differentiate. Zebrafish and Xenopus MK can induce neural tissues. In addition, deposits of MK and/or PTN are found in neurodegenerative diseases, such as Alzheimer's disease and multiple system atrophy. Both molecules are induced in reactive astrocytes by ischemic insults. In this context, it is interesting that LDL receptor-related protein is a receptor for MK and PTN, and this receptor has been implicated in the pathogenesis of Alzheimer's disease. MK and PTN share receptors, and show similar biological activities that include fibrinolytic, anti-apoptotic, mitogenic, transforming, angiogenic, and chemotactic ones. These activities explain how these molecules are involved in carcinogenesis. MK is detected in human carcinoma specimens from pre-cancerous stages to advanced stages. Strong expression of PTN is also detected in several carcinomas, although, in general, MK is expressed more intensely and in a wide range of carcinomas than PTN. The blood MK level is frequently elevated in advanced human carcinomas, decreases after surgical removal of the tumors, and is correlated with prognostic factors. Thus, it is a good market for evaluating the progress of carcinomas. Furthermore, antisense oligonucleotides for MK and ribozymes for PTN show anti-tumor activity. Therefore, MK and PTN are candidate molecular targets for therapy for human carcinomas.

HB-GAM/Pleiotrophin and Midkine are differently expressed and distributed during retinoic acid-induced neural differentiation of P19 cells

HB-GAM/Pleiotrophin and Midkine (MK) are developmentally-regulated proteins with putative functions during cell growth and differentiation. Using the P19 cell which is a model to study the events associated with early development, we examined the expression and cellular localization of HB-GAM and MK during neural differentiation of P19 cells induced by retinoic acid (RA). The temporal expressions of HB-GAM and MK transcripts and both the levels and cellular localizations of the corresponding proteins appeared dramatically different. MK mRNA, already expressed in untreated P19 cells, was transiently increased by exposure to RA and then largely down regulated. More interestingly, HB-GAM which was not detected in untreated P19 cells was strongly expressed after 2 days of RA treatment and this expression persists throughout the duration of the culture suggesting that it could be involved in different aspects of this differentiation process.

Vitamin A and infancy. Biochemical, functional, and clinical aspects

Vitamin A is a very intriguing natural compound. The molecule not only has a complex array of physiological functions, but also represents the precursor of promising and powerful new pharmacological agents. Although several aspects of human retinol metabolism, including absorption and tissue delivery, have been clarified, the type and amounts of vitamin A derivatives that are intracellularly produced remain quite elusive. In addition, their precise function and targets still need to be identified. Retinoic acids, undoubtedly, play a major role in explaining activities of retinol, but, recently, a large number of physiological functions have been attributed to different retinoids and to vitamin A itself. One of the primary roles this vitamin plays is in embryogenesis. Almost all steps in organogenesis are controlled by retinoic acids, thus suggesting that retinol is necessary for proper development of embryonic tissues. These considerations point to the dramatic importance of a sufficient intake of vitamin A and explain the consequences if intake of retinol is deficient. However, hypervitaminosis A also has a number of remarkable negative consequences, which, in same cases, could be fatal. Thus, the use of large doses of retinol in the treatment of some human diseases and the use of megavitamin therapy for certain chronic disorders as well as the growing tendency toward vitamin faddism should alert physicians to the possibility of vitamin overdose.

The molecular control of renal branching morphogenesis: current knowledge and emerging insights

Mammalian kidney development requires the formation of a patterned, branched network of collecting ducts, a process termed renal branching morphogenesis. Disruption of renal branching morphogenesis during human kidney development results in renal dysplasia, the major cause of renal failure in young children. Genetic evidence, combined with in vitro data, have implicated transcription factors, secreted growth factors, and cell surface signaling peptides as critical regulators of renal branching morphogenesis. This review discusses the current knowledge regarding the regulation of renal branching morphogenesis in vivo provided by the analysis of genetic mutations in mice and humans which disrupt collecting duct system development. In addition, in vivo and in vitro evidence regarding the functions of several other gene families are considered, rendering new insight into emerging regulatory roles for these molecules in renal branching morphogenesis.