Tissue injury after lithium treatment in human and rat postnatal kidney involves glycogen synthase kinase-3β-positive epithelium

Tubuloid differentiation to model the human distal nephron and collecting duct in health and disease

Organoid technology is rapidly gaining ground for studies on organ (patho)physiology. Tubuloids are long-term expanding organoids grown from adult kidney tissue or urine. The progenitor state of expanding tubuloids comes at the expense of differentiation. Here, we differentiate tubuloids to model the distal nephron and collecting ducts, essential functional parts of the kidney. Differentiation suppresses progenitor traits and upregulates genes required for function. A single-cell atlas reveals that differentiation predominantly generates thick ascending limb and principal cells. Differentiated human tubuloids express luminal NKCC2 and ENaC capable of diuretic-inhibitable electrolyte uptake and enable disease modeling as demonstrated by a lithium-induced tubulopathy model. Lithium causes hallmark AQP2 loss, induces proliferation, and upregulates inflammatory mediators, as seen in vivo. Lithium also suppresses electrolyte transport in multiple segments. In conclusion, this tubuloid model enables modeling of the human distal nephron and collecting duct in health and disease and provides opportunities to develop improved therapies.

Reduction of lithium induced interstitial fibrosis on co-administration with amiloride

Long-term administration of lithium is associated with chronic interstitial fibrosis that is partially reduced with exposure to amiloride. We examined potential pathways of how amiloride may reduce interstitial fibrosis. Amiloride was administered to a rat model of lithium induced interstitial fibrosis over a long term (6 months), as well as for short terms of 14 and 28 days. Kidney cortical tissue was subjected to RNA sequencing and microRNA expression analysis. Gene expression changes of interest were confirmed using immunohistochemistry on kidney tissue. Pathways identified by RNA sequencing of kidney tissue were related to 'promoting inflammation' for lithium and 'reducing inflammation' for amiloride. Validation of candidate genes found amiloride reduced inflammatory components induced by lithium including NF-κB/p65^Ser536 and activated pAKT^Ser473, and increased p53 mediated regulatory function through increased p21 in damaged tubular epithelial cells. Amiloride also reduced the amount of Notch1 positive PDGFrβ pericytes and infiltrating CD3 cells in the interstitium. Thus, amiloride attenuates a multitude of pro-inflammatory components induced by lithium. This suggests amiloride could be repurposed as a possible anti-inflammatory, anti-fibrotic agent to prevent or reduce the development of chronic interstitial fibrosis.

A serum proteomic study of two case-control cohorts identifies novel biomarkers for bipolar disorder

We set out to identify novel protein associations with potential as clinically viable biomarkers for bipolar disorder. To this end, we used proximity extension assay to analyze 201 unique proteins in blood serum from two independent cohorts comprising patients with bipolar disorder and healthy controls (total n = 493). We identified 32 proteins significantly associated with bipolar disorder in both case-control cohorts after adjusting for relevant covariates. Twenty-two findings are novel to bipolar disorder, but 10 proteins have previously been associated with bipolar disorder: chitinase-3-like protein 1, C-C motif chemokine 3 (CCL3), CCL4, CCL20, CCL25, interleukin 10, growth/differentiation factor-15, matrilysin (MMP-7), pro-adrenomedullin, and TNF-R1. Next, we estimated the variance in serum protein concentrations explained by psychiatric drugs and found that some case-control associations may have been driven by psychiatric drugs. The highest variance explained was observed between lithium use and MMP-7, and in post-hoc analyses and found that the serum concentration of MMP-7 was positively associated with serum lithium concentration, duration of lithium therapy, and inversely associated with estimated glomerular filtration rate in an interaction with lithium. This is noteworthy given that MMP-7 has been suggested as a mediator of renal tubulointerstitial fibrosis, which is characteristic of lithium-induced nephropathy. Finally, we used machine learning to evaluate the classification performance of the studied biomarkers but the average performance in unseen data was fair to moderate (area under the receiver operating curve = 0.72). Taken together, our serum biomarker findings provide novel insight to the etiopathology of bipolar disorder, and we present a suggestive biomarker for lithium-induced nephropathy.

[Chronic metabolic and renal disorders related to lithium salts treatment]

Lithium salts are the main treatment of bipolar disorder, which is characterized by potentially life-threatening maniac and/or depressive episodes. They have proven efficient in the prevention and treatment of acute episodes as well as in the prevention of suicidal risk. However, this efficacy is counterbalanced by a narrow therapeutic range that can lead to potentially harmful overdose, and by adverse long-term events. Nevertheless, they remain first-line treatment, notwithstanding therapeutic alternatives. In this review, we will describe toxic effects of long-term treatment at therapeutic levels of lithium salts. Regarding renal effects, early-impaired urine concentrating ability might lead to polyuria and polydipsia, and even to hypernatremia if free access to water is compromised. Long-term lithium treatment might also lead to chronic kidney disease, characterized by tubulo-interstitial multicystic nephropathy. End-stage renal disease requiring renal replacement therapy is a rare complication. Major extra-renal toxic effects are hypercalcemia and hypothyroidism. Treatment cessation due to these adverse events should be a multidisciplinary and case-by-case decision based on the benefit/risk ratio. Since these toxic effects are mild and display slow progression, treatment cessation is uncommon. However, regular medical and biological check-up is needed in order to prevent these disorders, and patients might be referred to nephrologists and/or endocrinologists once the disorders are established.

[Renal toxicity of lithium]

Besides its efficiency, lithium has a narrow therapeutic index and can result in considerable toxicity. Among the potential side effects, two types of renal toxicity are observed: a decreased renal concentrating ability and a chronic renal failure. Lithium-induced polyuria is frequent, estimated to affect up to 40% of patients, and develops usually early. It may be irreversible, especially if the treatment has been prescribed for more than 15 years. A chronic renal failure is observed in patients treated for more than 10 to 20 years. Its prevalence is estimated at 12% after 19 years of treatment. Some patients (0.5%) may reach end stage renal disease. The major risk factor is the duration of exposure to lithium. Discussion about stopping or not lithium in case of renal failure needs multidisciplinary expertise and depends on psychiatric status and renal function.

Thyroid and renal tumors in patients treated with long-term lithium: case series from a lithium clinic, review of the literature and international pharmacovigilance reports

BACKGROUND

Cancer had never been considered as a relevant problem in patients treated with lithium until 2015, when a document published by the European Medicine Agency concluded that long-term use of lithium might induce renal tumors. A few months later, we observed the case of a woman treated with lithium for 18 years who was diagnosed with both thyroid and renal tumors.

METHODS

This study aimed to investigate the correlation between lithium treatment and thyroid or renal tumors. We analyzed clinical records in our lithium clinic database, causes of death of patients who had been visited at least once at the lithium clinic, reports of lithium adverse reactions in the European and WHO pharmacovigilance databases, and published cases of thyroid and renal tumors in long-term lithium-treated patients.

RESULTS

Of the 1871 lithium patients who had been visited at least once between 1980 and 2013, eight had been diagnosed with thyroid papillary carcinoma and two with clear-cell renal-cell carcinoma. No cases of thyroid cancer and only one case of renal tumor were the cause of death according to the 375 available death certificates. VigiAccess database contained a total of 29 and 14 cases of renal and thyroid tumors, respectively. EudraVigilance database contained 21 cases of renal and 8 of thyroid neoplasms. Literature search yielded 6 published cases of thyroid papillary carcinoma and 25 cases of various renal tumors. However, two population-based studies did not find any increased risks of cancer in patients exposed to lithium, whereas two nationwide studies did not find any excess of renal tumors.

CONCLUSION

So far it has not been possible epidemiologically to confirm an increased risk of thyroid or renal cancers associated with lithium. Such a conclusion is supported by the findings of low rates and mortalities of thyroid or renal cancers from the present lithium clinic data.

PGE2 receptor EP3 inhibits water reabsorption and contributes to polyuria and kidney injury in a streptozotocin-induced mouse model of diabetes

AIMS/HYPOTHESIS

The first clinical manifestation of diabetes is polyuria. The prostaglandin E2 (PGE2) receptor EP3 antagonises arginine vasopressin (AVP)-mediated water reabsorption and its expression is increased in the diabetic kidney. The purpose of this work was to study the contribution of EP3 to diabetic polyuria and renal injury.

METHODS

Male Ep 3 (-/-) (also known as Ptger3 (-/-)) mice were treated with streptozotocin (STZ) to generate a mouse model of diabetes and renal function was evaluated after 12 weeks. Isolated collecting ducts (CDs) were microperfused to study the contribution of EP3 to AVP-mediated fluid reabsorption.

RESULTS

Ep 3 (-/-)-STZ mice exhibited attenuated polyuria and increased urine osmolality compared with wild-type STZ (WT-STZ) mice, suggesting enhanced water reabsorption. Compared with WT-STZ mice, Ep 3 (-/-)-STZ mice also had increased protein expression of aquaporin-1, aquaporin-2, and urea transporter A1, and reduced urinary AVP excretion, but increased medullary V2 receptors. In vitro microperfusion studies indicated that Ep 3 (-/-) and WT-STZ CDs responded to AVP stimulation similarly to those of wild-type mice, with a 60% increase in fluid reabsorption. In WT non-injected and WT-STZ mice, EP3 activation with sulprostone (PGE2 analogue) abrogated AVP-mediated water reabsorption; this effect was absent in mice lacking EP3. A major finding of this work is that Ep 3 (-/-)-STZ mice showed blunted renal cyclooxygenase-2 protein expression, reduced renal hypertrophy, reduced hyperfiltration and reduced albuminuria, as well as diminished tubular dilation and nuclear cysts.

CONCLUSIONS/INTERPRETATION

Taken together, the data suggest that EP3 contributes to diabetic polyuria by inhibiting expression of aquaporins and that it promotes renal injury during diabetes. EP3 may prove to be a promising target for more selective management of diabetic kidney disease.

Lithium treatment and cancer incidence in bipolar disorder

OBJECTIVES

To investigate whether there is an increased risk of cancer associated with lithium treatment in patients with bipolar disorder compared to the general population.

METHODS

A nationwide Swedish register study of incidence rate ratios (IRRs) of total cancer and site-specific cancer in the 50-84-year age range was carried out in patients with bipolar disorder (n = 5,442) with and without lithium treatment from July 2005 to December 2009 compared to the general population using linked information from The Swedish Cancer Register, The National Patient Register, and The Drug Prescription Register.

RESULTS

The overall cancer risk was not increased in patients with bipolar disorder. There was no difference in risk of unspecified cancer, neither in patients with lithium treatment compared to the general population [IRR = 1.04, 95% confidence interval (CI): 0.89-1.23] nor in patients with bipolar disorder without lithium treatment compared to the general population (IRR = 1.03, 95% CI: 0.89-1.19). The cancer risk was significantly increased in patients with bipolar disorder without lithium treatment in the digestive organs (IRR = 1.47, 95% CI: 1.12-1.93), in the respiratory system and intrathoracic organs (IRR = 1.72, 95% CI: 1.11-2.66), and in the endocrine glands and related structures (IRR = 2.60, 95% CI: 1.24-5.47), but in patients with bipolar disorder with lithium treatment, there was no significantly increased cancer risk compared to the general population.

CONCLUSIONS

Bipolar disorder was not associated with increased cancer incidence and neither was lithium treatment in these patients. Specifically, there was an increased risk of respiratory, gastrointestinal, and endocrine cancer in patients with bipolar disorder without lithium treatment.

Lithium in the Kidney: Friend and Foe?

Trace amounts of lithium are essential for our physical and mental health, and administration of lithium has improved the quality of life of millions of patients with bipolar disorder for >60 years. However, in a substantial number of patients with bipolar disorder, long-term lithium therapy comes at the cost of severe renal side effects, including nephrogenic diabetes insipidus and rarely, ESRD. Although the mechanisms underlying the lithium-induced renal pathologies are becoming clearer, several recent animal studies revealed that short-term administration of lower amounts of lithium prevents different forms of experimental AKI. In this review, we discuss the knowledge of the pathologic and therapeutic effects of lithium in the kidney. Furthermore, we discuss the underlying mechanisms of these seemingly paradoxical effects of lithium, in which fine-tuned regulation of glycogen synthase kinase type 3, a prime target for lithium, seems to be key. The new discoveries regarding the protective effect of lithium against AKI in rodents call for follow-up studies in humans and suggest that long-term therapy with low lithium concentrations could be beneficial in CKD.

Solid renal tumours of collecting duct origin in patients on chronic lithium therapy

Background

Lithium (Li) is an invaluable drug for the treatment of bipolar disorder. Long-term Li use is associated with renal complications including the formation of uncomplicated renal cysts caused by proliferation and expansion of collecting duct (CD) cells. We report six patients with complicated renal cysts in the context of Li nephropathy.

Methods

Over a time period of 15 years, we have identified six patients with one or more solid renal tumours in our population of approximately 50 patients with chronic Li nephropathy. In this study we describe the clinical and pathological characteristics of these Li-related tumours.

Results

All patients were on Li therapy for over 10 years and suffered from varying degrees of Li nephropathy. The tumours were all of CD origin and comprised both oncocytomas and collecting duct carcinomas. The CD carcinomas differed from the very rare “classical” CD cell carcinomas in histological appearance, multifocal presentation and non-aggressive clinical behaviour

Conclusions

The increased incidence of CD derived tumours and atypical presentation of CD cell carcinomas in patients with chronic Li nephropathy suggests that Li predisposes to the development of these tumours. We hypothesize that prolonged stimulation of CD cell proliferation and expansion by Li not only causes cyst formation, but can eventually induce the formation of adenomas and carcinomas. Increased awareness of a possible relationship between chronic Li therapy and renal neoplasms, will enhance the knowledge on epidemiology, clinical behavior and optimal therapy for the Li-related renal neoplasms.

Long-Term Lithium Use and Risk of Renal and Upper Urinary Tract Cancers

Lithium induces proliferation in the epithelium of renal collecting ducts. A recent small-scale cohort study reported a strong association between use of lithium and increased risk of renal neoplasia. We therefore conducted a large-scale pharmacoepidemiologic study of the association between long-term use of lithium and risk of upper urinary tract cancer, including renal cell cancer and cancers of the renal pelvis or ureter. We identified all histologically verified upper urinary tract cancer cases in Denmark between 2000 and 2012 from the Danish Cancer Registry. A total of 6477 cases were matched by age and sex to 259,080 cancer-free controls. Data on lithium use from 1995 to 2012 were obtained from the Danish Prescription Registry. We estimated the association between long-term use of lithium (≥5 years) and risk of upper urinary tract cancer using conditional logistic regression with adjustment for potential confounders. Long-term use of lithium was observed among 0.22% of cases and 0.17% of controls. This yielded an overall nonsignificant adjusted odds ratio (OR) of 1.3 (95% confidence interval [95% CI], 0.8-2.2) for upper urinary tract cancer associated with long-term use of lithium. Analyses stratified by stage and subtype of upper urinary tract cancer revealed slight but nonsignificant increases in the ORs for localized disease (OR, 1.6; 95% CI, 0.8-3.0) and for renal pelvis/ureter cancers (OR, 1.7; 95% CI, 0.5-5.4). In conclusion, in our nationwide case-control study, use of lithium was not associated with an increased risk of upper urinary tract cancer.

Glycogen synthase kinase-3β promotes cyst expansion in polycystic kidney disease

Polycystic kidney diseases (PKDs) are inherited disorders characterized by the formation of fluid filled renal cysts. Elevated cAMP levels in PKDs stimulate progressive cyst enlargement involving cell proliferation and transepithelial fluid secretion often leading to end stage renal disease. The glycogen synthase kinase-3 (GSK3) family of protein kinases consists of GSK3α and GSK3β isoforms and plays a crucial role in multiple cellular signaling pathways. We previously found that GSK3β, a regulator of cell proliferation, is also crucial for cAMP generation and vasopressin mediated urine concentration by the kidneys. However, the role of GSK3β in the pathogenesis of PKDs is not known. Here we found that GSK3β expression and activity were markedly up-regulated and associated with cyst-lining epithelia in the kidneys of mice and humans with PKD. Renal collecting duct specific gene knockout of GSK3β or pharmacological inhibition of GSK3 effectively slowed the progression of PKD in mouse models of autosomal recessive or autosomal dominant PKD. GSK3 inactivation inhibited cAMP generation and cell proliferation resulting in reduced cyst expansion, improved renal function and extended lifespan. GSK3β inhibition also reduced pERK, c-Myc and Cyclin-D1, known mitogens in proliferation of cystic epithelial cells. Thus, GSK3β plays a novel functional role in PKD pathophysiology and its inhibition may be therapeutically useful to slow cyst expansion and progression of PKD.

Glycogen synthase kinase 3α regulates urine concentrating mechanism in mice

In mammals, glycogen synthase kinase (GSK)3 comprises GSK3α and GSK3β isoforms. GSK3β has been shown to play a role in the ability of kidneys to concentrate urine by regulating vasopressin-mediated water permeability of collecting ducts, whereas the role of GSK3α has yet to be discerned. To investigate the role of GSK3α in urine concentration, we compared GSK3α knockout (GSK3αKO) mice with wild-type (WT) littermates. Under normal conditions, GSK3αKO mice had higher water intake and urine output. GSK3αKO mice also showed reduced urine osmolality and aquaporin-2 levels but higher urinary vasopressin. When water deprived, they failed to concentrate their urine to the same level as WT littermates. The addition of 1-desamino-8-d-arginine vasopressin to isolated inner medullary collecting ducts increased the cAMP response in WT mice, but this response was reduced in GSK3αKO mice, suggesting reduced responsiveness to vasopressin. Gene silencing of GSK3α in mpkCCD cells also reduced forskolin-induced aquaporin-2 expression. When treated with LiCl, an isoform nonselective inhibitor of GSK3 and known inducer of polyuria, WT mice developed significant polyuria within 6 days. However, in GSK3αKO mice, the polyuric response was markedly reduced. This study demonstrates, for the first time, that GSK3α could play a crucial role in renal urine concentration and suggest that GSK3α might be one of the initial targets of Li(+) in LiCl-induced nephrogenic diabetes insipidus.

Lithium induces microcysts and polyuria in adolescent rat kidney independent of cyclooxygenase-2

In patients, chronic treatment with lithium leads to renal microcysts and nephrogenic diabetes insipidus (NDI). It was hypothesized that renal cyclooxygenase‐2 (COX‐2) activity promotes microcyst formation and NDI. Kidney microcysts were induced in male adolescent rats by feeding dams with lithium (50 mmol/kg chow) from postnatal days 7–34. Lithium treatment induced somatic growth retardation, renal microcysts and dilatations in cortical collecting duct; it increased cortical cell proliferation and inactive pGSK‐3β abundance; it lowered aquaporin‐2 (AQP2) protein abundance and induced polyuria with decreased ability to concentrate the urine; and it increased COX‐2 protein level in thick ascending limb. Concomitant treatment with lithium and a specific COX‐2 inhibitor, parecoxib (5 mg/kg per day, P10–P34), did not prevent lithium‐induced microcysts and polyuria, but improved urine concentrating ability transiently after a 1‐desamino‐8‐D‐arginine vasopressin challenge. COX‐2 inhibition did not reduce cortical lithium‐induced cell proliferation and phosphorylation of glycogen synthase kinase‐3β (GSK‐3β). COX‐1 protein abundance increased in rat kidney cortex in response to lithium. COX‐1 immunoreactivity was found in microcyst epithelium in rat kidney. A human nephrectomy specimen from a patient treated for 28 years with lithium displayed multiple, COX‐1‐immunopositive, microcysts. In chronic lithium‐treated adolescent rats, COX‐2 is not colocalized with microcystic epithelium, mitotic activity, and inactive pGSK‐3β in collecting duct; a blocker of COX‐2 does not prevent cell proliferation, cyst formation, or GSK‐3β inactivation. It is concluded that COX‐2 activity is not the primary cause for microcysts and polyuria in a NaCl‐substituted rat model of lithium nephropathy. COX‐1 is a relevant candidate to affect the injured epithelium.

Long‐term use of lithium is associated with development of microcysts in the kidney. In this study the role for cyclooxygenase‐2 (COX‐2)‐derived prostaglandins in cyst formation was tested in a rat model. Inhibition of COX‐2 did not resolve or prevent kidney injury. COX‐1 was associated with the cyst epithelium and is more likely to play a functional role.

Lithium causes G2 arrest of renal principal cells

Vasopressin-regulated expression and insertion of aquaporin-2 channels in the luminal membrane of renal principal cells is essential for urine concentration. Lithium affects urine concentrating ability, and approximately 20% of patients treated with lithium develop nephrogenic diabetes insipidus (NDI), a disorder characterized by polyuria and polydipsia. Lithium-induced NDI is caused by aquaporin-2 downregulation and a reduced ratio of principal/intercalated cells, yet lithium induces principal cell proliferation. Here, we studied how lithium-induced principal cell proliferation can lead to a reduced ratio of principal/intercalated cells using two-dimensional and three-dimensional polarized cultures of mouse renal collecting duct cells and mice treated with clinically relevant lithium concentrations. DNA image cytometry and immunoblotting revealed that lithium initiated proliferation of mouse renal collecting duct cells but also increased the G2/S ratio, indicating G2/M phase arrest. In mice, treatment with lithium for 4, 7, 10, or 13 days led to features of NDI and an increase in the number of principal cells expressing PCNA in the papilla. Remarkably, 30%-40% of the PCNA-positive principal cells also expressed pHistone-H3, a late G2/M phase marker detected in approximately 20% of cells during undisturbed proliferation. Our data reveal that lithium treatment initiates proliferation of renal principal cells but that a significant percentage of these cells are arrested in the late G2 phase, which explains the reduced principal/intercalated cell ratio and may identify the molecular pathway underlying the development of lithium-induced renal fibrosis.

Regulation of mineral metabolism by lithium

Lithium, an inhibitor of glycogen synthase kinase 3 (GSK3), is widely used for the treatment of mood disorders. Side effects of lithium include nephrogenic diabetes insipidus, leading to renal water loss. Dehydration has in turn been shown to downregulate Klotho, which is required as co-receptor for the downregulation of 1,25(OH)2D3 formation by fibroblast growth factor 23 (FGF23). FGF23 decreases and 1,25(OH)2D3 stimulates renal tubular phosphate reabsorption. The present study explored whether lithium influences renal Klotho expression, FGF23 serum levels, 1,25(OH)2D3 formation, and renal phosphate excretion. To this end, mice were analyzed after a 14-day period of sham treatment or of treatment with lithium (200 mg/kg/day subcutaneously). Serum antidiuretic hormone (ADH), FGF23, and 1,25(OH)2D3 concentrations were determined by ELISA or EIA, renal Klotho protein abundance and GSK3 phosphorylation were analyzed by Western blotting, and serum phosphate and calcium concentration by photometry. Lithium treatment significantly increased renal GSK3 phosphorylation, enhanced serum ADH and FGF23 concentrations, downregulated renal Klotho expression, stimulated renal calcium and phosphate excretion, and decreased serum 1,25(OH)2D3 and phosphate concentrations. In conclusion, lithium treatment upregulates FGF23 formation, an effect paralleled by substantial decrease of serum 1,25(OH)2D3, and phosphate concentrations and thus possibly affecting tissue calcification.

Rapamycin inhibition of mTORC1 reverses lithium-induced proliferation of renal collecting duct cells

Nephrogenic diabetes insipidus (NDI) is the most common renal side effect in patients undergoing lithium therapy for bipolar affective disorders. Approximately 2 million US patients take lithium of whom ∼50% will have altered renal function and develop NDI (2, 37). Lithium-induced NDI is a defect in the urinary concentrating mechanism. Lithium therapy also leads to proliferation and abundant renal cysts (microcysts), commonly in the collecting ducts of the cortico-medullary region. The mTOR pathway integrates nutrient and mitogen signals to control cell proliferation and cell growth (size) via the mTOR Complex 1 (mTORC1). To address our hypothesis that mTOR activation may be responsible for lithium-induced proliferation of collecting ducts, we fed mice lithium chronically and assessed mTORC1 signaling in the renal medulla. We demonstrate that mTOR signaling is activated in the renal collecting ducts of lithium-treated mice; lithium increased the phosphorylation of rS6 (Ser240/Ser244), p-TSC2 (Thr1462), and p-mTOR (Ser2448). Consistent with our hypothesis, treatment with rapamycin, an allosteric inhibitor of mTOR, reversed lithium-induced proliferation of medullary collecting duct cells and reduced levels of p-rS6 and p-mTOR. Medullary levels of p-GSK3β were increased in the renal medullas of lithium-treated mice and remained elevated following rapamycin treatment. However, mTOR inhibition did not improve lithium-induced NDI and did not restore the expression of collecting duct proteins aquaporin-2 or UT-A1.

Lithium: a versatile tool for understanding renal physiology

By virtue of its unique interactions with kidney cells, lithium became an important research tool in renal physiology and pathophysiology. Investigators have uncovered the intricate relationships of lithium with the vasopressin and aldosterone systems, and the membrane channels or transporters regulated by them. While doing so, their work has also led to 1) questioning the role of adenylyl cyclase activity and prostaglandins in lithium-induced suppression of aquaporin-2 gene transcription; 2) unraveling the role of purinergic signaling in lithium-induced polyuria; and 3) highlighting the importance of the epithelial sodium channel (ENaC) in lithium-induced nephrogenic diabetes insipidus (NDI). Lithium-induced remodeling of the collecting duct has the potential to shed new light on collecting duct remodeling in disease conditions, such as diabetes insipidus. The finding that lithium inhibits glycogen synthase kinase-3β (GSK3β) has opened an avenue for studies on the role of GSK3β in urinary concentration, and GSK isoforms in renal development. Finally, proteomic and metabolomic profiling of the kidney and urine in rats treated with lithium is providing insights into how the kidney adapts its metabolism in conditions such as acquired NDI and the multifactorial nature of lithium-induced NDI. This review provides state-of-the-art knowledge of lithium as a versatile tool for understanding the molecular physiology of the kidney, and a comprehensive view of how this tool is challenging some of our long-standing concepts in renal physiology, often with paradigm shifts, and presenting paradoxical situations in renal pathophysiology. In addition, this review points to future directions in research where lithium can lead the renal community.

Glycogen synthase kinase-3 regulation of urinary concentrating ability

PURPOSE OF REVIEW

Glycogen synthase kinase-3 (GSK3) is an enzyme that is gaining prominence as a critical signaling molecule in the epithelial cells of renal tubules. This review will focus on recent findings exploring the role of GSK3 in renal collecting ducts, especially its role in urine concentration involving vasopressin signaling.

RECENT FINDINGS

Recent studies using inhibition or tissue-specific gene deletion of GSK3 revealed the mechanism by which GSK3 regulates aquaporin 2 water channels via adenylate cyclase or the prostaglandin-E2 pathway. In other studies, postnatal treatment with lithium, an inhibitor of GSK3, increased cell proliferation and led to microcyst formation in rat kidneys. These studies suggest that loss of GSK3 activity could interfere with renal water transport at two levels. In the short term, it could disrupt vasopressin signaling in collecting duct cells and in the long term it could alter the structure of the collecting ducts, making them less responsive to the hydro-osmotic effects of vasopressin.

SUMMARY

Ongoing studies reveal the crucial role played by GSK3 in the regulation of vasopressin action in the renal collecting ducts and suggest a possible use of GSK3 inhibitors in disease conditions associated with disrupted vasopressin signaling.