Mevalonate kinase deficiency leads to decreased prenylation of Rab GTPases.

Mevalonate kinase deficiency (MKD) is caused by mutations in a key enzyme of the mevalonate-cholesterol biosynthesis pathway, leading to recurrent autoinflammatory disease characterised by enhanced release of interleukin-1ß (IL-1ß). It is currently believed that the inflammatory phenotype of MKD is triggered by temperature-sensitive loss of mevalonate kinase activity and reduced biosynthesis of isoprenoid lipids required for the prenylation of small GTPase proteins. However, previous studies have not clearly shown any change in protein prenylation in patient cells under normal conditions. With lymphoblast cell lines from two compound heterozygous MKD patients, we used a highly sensitive in vitro prenylation assay, together with quantitative mass spectrometry, to reveal a subtle accumulation of unprenylated Rab GTPases in cells cultured for 3 days or more at 40 °C compared with 37 °C. This included a 200% increase in unprenylated Rab7A, Rab14 and Rab1A. Inhibition of sterol regulatory element-binding protein (SREBP) activation by fatostatin led to more pronounced accumulation of unprenylated Rab proteins in MKD cells but not parent cells, suggesting that cultured MKD cells may partially overcome the loss of isoprenoid lipids by SREBP-mediated upregulation of enzymes required for isoprenoid biosynthesis. Furthermore, while inhibition of Rho/Rac/Rap prenylation promoted the release of IL-1ß, specific inhibition of Rab prenylation by NE10790 had no effect in human peripheral blood mononuclear cells or human THP-1 monocytic cells. These studies demonstrate for the first time that mutations in mevalonate kinase can lead to a mild, temperature-induced defect in the prenylation of small GTPases, but that loss of prenylated Rab GTPases is not the cause of enhanced IL-1ß release in MKD.

Unprenylated RhoA contributes to IL-1ß hypersecretion in mevalonate kinase deficiency model through stimulation of Rac1 activity.

Protein prenylation is a post-translational modification whereby non-sterol isoprenoid lipid chains are added, thereby modifying the molecular partners with which proteins interact. The autoinflammatory disease mevalonate kinase deficiency (MKD) is characterized by a severe reduction in protein prenylation. A major class of proteins that are affected are small GTPases, including Rac1 and RhoA. It is not clear how protein prenylation of small GTPases relates to GTP hydrolysis activity and downstream signaling. Here, we investigated the contribution of RhoA prenylation to the biochemical pathways that underlie MKD-associated IL-1ß hypersecretion using human cell cultures, Rac1 and RhoA protein variants, and pharmacological inhibitors. We found that when unprenylated, the GTP-bound levels of RhoA decrease, causing a reduction in GTPase activity and increased protein kinase B (PKB) phosphorylation. Cells expressing unprenylated RhoA produce increased levels of interleukin 1ß mRNA. Of other phenotypic cellular changes seen in MKD, increased mitochondrial potential and mitochondrial elongation, only mitochondrial elongation was observed. Finally, we show that pharmacological inactivation of RhoA boosts Rac1 activity, a small GTPase whose activity was earlier implied in MKD pathogenesis. Together, our data show that RhoA plays a pivotal role in MKD pathogenesis through Rac1/PKB signaling toward interleukin 1ß production and elucidate the effects of protein prenylation in monocytes.

Mevalonate kinase deficiency and neuroinflammation: balance between apoptosis and pyroptosis.

Mevalonic aciduria, a rare autosomal recessive disease, represents the most severe form of the periodic fever, known as Mevalonate Kinase Deficiency. This disease is caused by the mutation of the MVK gene, which codes for the enzyme mevalonate kinase, along the cholesterol pathway. Mevalonic aciduria patients show recurrent fever episodes with associated inflammatory symptoms, severe neurologic impairments, or death, in early childhood. The typical neurodegeneration occurring in mevalonic aciduria is linked both to the intrinsic apoptosis pathway (caspase-3 and -9), which is triggered by mitochondrial damage, and to pyroptosis (caspase-1). These cell death mechanisms seem to be also related to the assembly of the inflammasome, which may, in turn, activate pro-inflammatory cytokines and chemokines. Thus, this particular molecular platform may play a crucial role in neuroinflammation mechanisms. Nowadays, a specific therapy is still lacking and the pathogenic mechanisms involving neuroinflammation and neuronal dysfunction have not yet been completely understood, making mevalonic aciduria an orphan drug disease. This review aims to analyze the relationship among neuroinflammation, mitochondrial damage, programmed cell death, and neurodegeneration. Targeting inflammation and degeneration in the central nervous system might help identify promising treatment approaches for mevalonic aciduria or other diseases in which these mechanisms are involved.

Incidence and clinical features of hyperimmunoglobulinemia D and periodic fever syndrome (HIDS) and spectrum of mevalonate kinase (MVK) mutations in German children.

Autoinflammatory diseases (AIDs) are characterized by recurrent, self-limiting systemic inflammation. Disorders include hereditary recurrent fever (HRF) syndromes such as hyperimmunoglobulinemia D and periodic fever syndrome (HIDS). To determine the incidence of HIDS and report clinical and genetic characteristics together with the underlying MVK genotypes in German children, a prospective active surveillance was conducted in Germany during a period of 3 years. Monthly inquiries were sent to 370 children's hospitals by the German Paediatric Surveillance Unit (Clinic-ESPED, n1) and to two laboratories (Laboratory-ESPED, n2) performing genetic analyses. Inclusion criteria were a MVK mutation-positive patient ≤16 years of age with more than three self-limiting episodes of fever >38.5°C associated with increased inflammation markers. Clinical, epidemiological, and genetic data were assessed via questionnaires. Eight out of 16 patients were identified in Clinic-ESPED (n1) and 15 of 16 in Laboratory-ESPED (n2). Clinical and laboratory surveys overlapped in 7 of 16 cases. Incidence of HIDS was estimated to be 0.39 (95% CI: 0.22, 0.64) per 10(6) person-years. HIDS symptoms generally started in infancy with recurrent fever episodes lasting 3-12 (median, 4.5) days and recurring every 1-12 weeks. Fever was accompanied by abdominal pain, vomiting, diarrhea, cervical lymphadenopathy, and sometimes by headache, skin and joint symptoms. The patients carried 11 different MVK mutations mostly in compound heterozygosity (75%, 12 out of 16). The most frequent mutation was p.Val377Ile (81%, 13 out of 16). In Germany, the incidence of HIDS is very low with 0.39 per 10(6) person-years.

The farnesyltransferase inhibitors tipifarnib and lonafarnib inhibit cytokines secretion in a cellular model of mevalonate kinase deficiency.

The shortage of geranylgeranyl-pyrophosphate (GGPP) was associated to an increased IL-1ß release in the autoinflammatory syndrome mevalonate kinase deficiency (MKD), a rare inherited disease that has no specific therapy. Farnesyltransferase inhibitors (FTIs) act at the end of mevalonate pathway. Two FTIs, tipifarnib (Tip) and lonafarnib (Lon), were therefore evaluated as possible therapeutical choices for the treatment of MKD. FTIs could lead to a redirection of the limited available number of mevalonate intermediates preferentially to GGPP synthesis, eventually preventing the uncontrolled inflammatory response. The effect of Tip and Lon on intracellular cholesterol level (ICL) and on proinflammatory cytokines secretion was evaluated in a cellular model of MKD, chemically obtained treating RAW 264.7 cells with lovastatin (Lova) and alendronate (Ald). The combination of FTIs with the isoprenoid geraniol (GOH) was also tested both in this model and in monocytes isolated from MKD patients. Tip and Lon proved to revert the ICL lowering and to significantly reduce the lipopolysaccharide-induced cytokines secretion in Ald-Lova -RAW 264.7 cells. This anti-inflammatory effect was amplified combining the use of GOH with FTIs. The effect of GOH and Tip was successfully replicated in MKD patients' monocytes. Tip and Lon showed a dramatic anti-inflammatory effect in monocytes where mevalonate pathway was chemically or genetically impaired.

Mevalonate Kinase Deficiency and Squalene Synthase Inhibitor (TAK-475): The Balance to Extinguish the Inflammation.

Mevalonate Kinase Deficiency (MKD) is a rare inborn disease belonging to the family of periodic fever syndromes. The MKD phenotype is characterized by systemic inflammation involving multiple organs, including the nervous system. Current anti-inflammatory approaches to MKD are only partially effective and do not act specifically on neural inflammation. According to the new emerging pharmacology trends, the repositioning of drugs from the indication for which they were originally intended to another one can make mechanistic-based medications easily available to treat rare diseases. According to this perspective, the squalene synthase inhibitor Lapaquistat (TAK-475), originally developed as a cholesterol-lowering drug, might find a new indication in MKD, by modulating the mevalonate cholesterol pathway, increasing the availability of anti-inflammatory isoprenoid intermediates. Using an in vitro model for MKD, we mimicked the blockade of the cholesterol pathway and evaluated the potential anti-inflammatory effect of Lapaquistat. The results obtained showed anti-inflammatory effects of Lapaquistat in association with a low blockade of the metabolic pathway, while this effect did not remain with a tighter blockade. On these bases, Lapaquistat could be configured as an effective treatment for MKD's mild forms, in which the residual enzymatic activity is only reduced and not almost completely absent as in the severe forms.

Compromized geranylgeranylation of RhoA and Rac1 in mevalonate kinase deficiency.

Mevalonate kinase deficiency (MKD) is an autoinflammatory disorder caused by mutations in the MVK gene resulting in decreased activity of the enzyme mevalonate kinase (MK). Although MK is required for biosynthesis of all isoprenoids, in MKD, in particular, the timely synthesis of geranylgeranyl pyrophosphate appears to be compromised. Because small guanosine triphosphatases (GTPases) depend on geranylgeranylation for their proper signaling function, we studied the effect of MK deficiency on geranylgeranylation and activation of the two small GTPases, RhoA and Rac1. We demonstrate that both geranylgeranylation and activation of the two GTPases are more easily disturbed in MKD cells than in control cells when the flux though the isoprenoid biosynthesis pathway is suppressed by low concentrations of simvastatin. The limited capacity of geranylgeranylation in MKD cells readily leads to markedly increased levels of nonisoprenylated and activated GTPases, which will affect proper signaling by these GTPases.

[Utility of denaturing high performance liquid chromatography (DHPLC) for the diagnosis of mevalonate kinase deficiency in periodic disease]. / Utilità della tecnica denaturing high performance liquid chromatography (DHPLC) per la diagnosi di deficit di mevalonato chinasi nelle febbri periodiche di sospetta natura autoinfiammatoria.

OBJECTIVES: We developed a genetic investigation using denaturing high performance liquid chromatography (DHPLC), in order to identify polymorphisms of the gene MVK in patients with autoinflammatory syndrome suspicion. METHODS: We evaluated 19 patients affected by recurrent fevers and other clinical manifestations usually found in autoinflammatory syndromes and not correlated with infections or autoimmune disease and 10 healthy controls. IgD level was measured in all patients. Molecular testing was performed in DNA extracted from PBMC and MVK gene was analysed either with DHPLC or with automatic sequencer. Primers for PCR amplifications, amplicon lengths and PCR conditions were designed in our laboratory. RESULTS: IgD level was normal in 14 patients. Healthy controls did not show any alteration of the DHPLC-profiles and of the DNA sequences. Twelve patients had at least one altered DHPLC-profile and these data have been confirmed by sequencing. In particular we detected the polymorphisms c.78+61A>G, S52N, S135S, D170D, c.632-18A>G, c.885+24G>A already described in the database INFEVERS. With DHPLC we got the results in shorter time (10 hours/patient) and with lower cost (40 euro/patient) in comparison to direct sequencing (25 hours and 150 euro/patient). CONCLUSIONS: High IgD levels do not represent an essential marker for diagnosis of MKD, as already reported in literature. DHPLC is a rapid low cost technique in order to screen mutations in patients with MKD suspicion. Twelve patients carried at the same time D170D and c.632-18A>G: such event suggests that these SNPs could be in linkage disequilibrium and that such polymorphisms could predispose to MKD.

Quantification of mevalonate-5-phosphate using UPLC-MS/MS for determination of mevalonate kinase activity.

OBJECTIVES: Mevalonate kinase deficiency, a rare autosomal recessive autoinflammatory disease, is caused by mutations in the MVK gene encoding mevalonate kinase (MK). MK catalyzes the phosphorylation of mevalonic acid to mevalonate-5-phosphate (MVAP) in the pathway of isoprenoid and sterol synthesis. The disease phenotype correlates with residual activity ranging from <0.5% for mevalonic aciduria to 1-7% for the milder hyperimmunoglobulinemia D and periodic fever syndrome (HIDS). Hence, assessment of loss-of-function requires high accuracy measurements. We describe a method using isotope dilution UPLC-MS/MS for precise and sensitive determination of MK activity. DESIGN AND METHODS: Wild-type MK and the variant V261A, which is associated with HIDS, were recombinantly expressed in Escherichia coli. Enzyme activity was determined by formation of MVAP over time quantified by isotope dilution UPLC-MS/MS. The method was validated according to the FDA Guidance for Bioanalytical Method Validation. RESULTS: Sensitivity for detection of MAVP by UPLC-MS/MS was improved by derivatization with butanol-HCl (LLOQ, 5.0 fmol) and the method was linear from 0.5 to 250 µmol/L (R(2) > 0.99) with a precision of ≥ 89% and an accuracy of ± 2.7%. The imprecision of the activity assay, including the enzymatic reaction and the UPLC-MS/MS quantification, was 8.3%. The variant V261A showed a significantly decreased activity of 53.1%. CONCLUSION: Accurate determination of MK activity was enabled by sensitive and reproducible detection of MVAP using UPLC-MS/MS. The novel method may improve molecular characterization of MVK mutations, provide robust genotype-phenotype correlations, and accelerate compound screening for drug candidates restoring variant MK activity.

Sterol metabolism disorders and neurodevelopment-an update.

Cholesterol has numerous quintessential functions in normal cell physiology, as well as in embryonic and postnatal development. It is a major component of cell membranes and myelin, and is a precursor of steroid hormones and bile acids. The development of the blood brain barrier likely around 12-18 weeks of human gestation makes the developing embryonic/fetal brain dependent on endogenous cholesterol synthesis. Known enzyme defects along the cholesterol biosynthetic pathway result in a host of neurodevelopmental and behavioral findings along with CNS structural anomalies. In this article, we review sterol synthesis disorders in the pre- and post-squalene pathway highlighting neurodevelopmental aspects that underlie the clinical presentations and course of Smith-Lemli-Opitz Syndrome (SLOS), mevalonic aciduria (MVA) or the milder version hyper-immunoglobulinemia D and periodic fever syndrome (HIDS), Antley-Bixler syndrome with genital anomalies and disordered steroidogenesis (ABS1), congenital hemidysplasia with icthyosiform nevus and limb defects (CHILD) syndrome, CK syndrome, sterol C4 methyl oxidase (SC4MOL) deficiency, X-linked dominant chondrodysplasia punctata 2(CDPX2)/ Conradi Hunermann syndrome, lathosterolosis and desmosterolosis, We also discuss current controversies and share thoughts on future directions in the field.

Mevalonate kinase deficiency (hyper IgD syndrome with periodic fever)--different faces with separate treatments: two cases and review of the literature.

The hyperimmunoglobulinemia D syndrome (HIDS), so-called mevalonate kinase deficiency, is caused by recessive mutations in the gene encoding mevalonate kinase enzyme. HIDS is characterized by recurrent fever attacks of 3-7 days that begin in infancy and recur every 4-6 weeks. The febrile period is accompanied by lymphadenopathy, arthralgia, abdominal pain, diarrhea, aphthous ulcers, and varying degree of skin involvement. The course and severity of the disease may be quite different. There is no effective or proven therapy for HIDS. We report two cases with HIDS, which had separate clinical findings and treatment strategies.

Specific increase in caspase-1 activity and secretion of IL-1 family cytokines: a putative link between mevalonate kinase deficiency and inflammation.

The mevalonate kinase deficiency (MKD), including hyperimmunoglobulinemia D periodic fever syndrome (HIDS) and the more severe mevalonic aciduria are rare, autosomal recessive, autoinflammatory diseases belonging to the hereditary periodic fever (HPF) family. Other members include: familial mediterranean fever (FMF), the cryopyrin-associated periodic syndromes (CAPS) and TNFR-associated periodic syndromes (TRAPS). MKD is caused by mutations in the gene encoding mevalonate kinase (MK), an enzyme of the cholesterol pathway, leading to its inactivation. The molecular mechanisms linking MKD and abnormalities of isoprenoid biosynthesis to cytokine production and inflammation have yet to be fully elucidated. Statins, which are extensively prescribed for lowering cholesterol, are potent inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase, the enzyme directly upstream of MK. In this review, we discuss recent reports demonstrating that in vitro inhibition of the mevalonate pathway by statins specifically increases the production, by activated monocytes, of cytokines of the IL-1 family, by enhancing caspase-1 activity, the enzyme responsible for IL-1beta and IL-18 maturation. The molecular mechanisms involve geranylgeranylation and the enhancement of the activity of G proteins such as Rac-1. Interestingly, activated fibroblasts from MKD patients secrete more IL-1beta than fibroblasts from healthy donors. Taken together, these data highlight the specific enhancement of the IL-1 family of cytokines, the maturation of which is caspase-1-dependent in MKD. Finally, the spectacular decrease in febrile attacks in patients with severe HIDS under IL-1 receptor antagonist (anakinra) treatment, reinforces this hypothesis. Deregulated caspase-1 activation could be responsible for the inflammatory component of MKD, thereby mechanistically linking MKD to FMF and CAPS through cytokines of the IL-1 family.