A noncompetitive BACE1 inhibitor TAK-070 ameliorates Abeta pathology and behavioral deficits in a mouse model of Alzheimer's disease.

We discovered a nonpeptidic compound, TAK-070, that inhibited BACE1, a rate-limiting protease for the generation of Abeta peptides that are considered causative for Alzheimer's disease (AD), in a noncompetitive manner. TAK-070 bound to full-length BACE1, but not to truncated BACE1 lacking the transmembrane domain. Short-term oral administration of TAK-070 decreased the brain levels of soluble Abeta, increased that of neurotrophic sAPPalpha by approximately 20%, and normalized the behavioral impairments in cognitive tests in Tg2576 mice, an APP transgenic mouse model of AD. Six-month chronic treatment decreased cerebral Abeta deposition by approximately 60%, preserving the pharmacological efficacy on soluble Abeta and sAPPalpha levels. These results support the feasibility of BACE1 inhibition with a noncompetitive inhibitor as disease-modifying as well as symptomatic therapy for AD.

High-molecular-weight beta-amyloid oligomers are elevated in cerebrospinal fluid of Alzheimer patients.

There is accumulating evidence that soluble amyloid-beta (Abeta) oligomers, rather than amyloid fibrils, are the principal pathogenic species in Alzheimer disease (AD). Here, we have developed a novel enzyme-linked immunosorbent assay (ELISA) specific for high-molecular-weight (HMW) Abeta oligomers. Analysis of Abeta oligomers derived from synthetic Abeta 1-42, by size-exclusion chromatography (SEC), revealed that our ELISA specifically detected HMW Abeta oligomers of 40-200 kDa. Using this ELISA, we detected significantly higher (P<0.0001) signals in cerebrospinal fluid (CSF) samples from 25 patients with AD or mild cognitive impairment (MCI), compared to 25 age-matched controls. As a test for discriminating between the AD/MCI and control groups, the area under the curve in receiver operating characteristic analysis for the CSF HMW Abeta oligomers was greater than that for CSF Abeta x-42. Furthermore, the CSF levels of HMW Abeta oligomers showed a negative correlation with Mini-Mental State Examination scores in the AD/MCI group. We conclude that the CSF HMW Abeta oligomers detected by our ELISA could be useful as a diagnostic marker for AD, and also as a potential surrogate marker for disease severity. Our results support the idea that soluble HMW Abeta oligomers play a critical role in the pathogenesis and progression of AD.

Rapid progression from mild cognitive impairment to Alzheimer's disease in subjects with elevated levels of tau in cerebrospinal fluid and the APOE epsilon4/epsilon4 genotype.

BACKGROUND/AIMS: Increased cerebrospinal fluid (CSF) tau, decreased CSF amyloid-beta42 (Abeta42) and the apolipoprotein E gene (APOE) epsilon4 allele predict progression from mild cognitive impairment (MCI) to Alzheimer's disease (AD). Here, we investigated these markers to assess their predictive value and influence on the rate of disease progression. METHODS: Using ELISA, we measured the CSF biomarkers in 47 AD patients, 58 patients with MCI and 35 healthy control subjects. Twenty-eight MCI patients revisited the clinic and half of them progressed to AD during a period of 3-12 years. RESULTS: The expected changes in CSF total (T)-tau, phosphorylated (P)-tau and Abeta42 levels were found in AD, confirming the diagnostic value of these biomarkers. We were also able to corroborate an increased risk for progression from MCI to AD with elevated CSF T-tau and P-tau and with the presence of the APOE epsilon4/epsilon4 genotype, but not with decreased Abeta42. Finally, for the first time we demonstrated that MCI subjects with high CSF T-tau or P-tau and APOE epsilon4 homozygosity progressed faster from MCI to AD. CONCLUSIONS: CSF T-tau and P-tau as well as the APOE epsilon4/epsilon4 genotype are robust predictors of AD and are also associated with a more rapid progression from MCI to AD.

Expression of APP pathway mRNAs and proteins in Alzheimer's disease.

In both trisomy 21 and rare cases of triplication of amyloid precursor protein (APP) Alzheimer's disease (AD) pathological changes are believed to be secondary to increased expression of APP. We hypothesized that sporadic AD may also be associated with changes in transcription of APP or its metabolic partners. To address this issue, temporal neocortex of 27 AD and 21 non-demented control brains was examined to assess mRNA levels of APP isoforms (total APP, APP containing the Kunitz protease inhibitor domain [APP-KPI] and APP770) and APP metabolic enzymatic partners (the APP cleaving enzymes beta-secretase [BACE] and presenilin-1 [PS-1], and putative clearance molecules, low-density lipoprotein receptor protein [LRP] and apolipoprotein E [apoE]). Furthermore, we evaluated how changes in APP at the mRNA level affect the amount of Tris buffer extractable APP protein and Abeta40 and 42 peptides in AD and control brains. As assessed by quantitative PCR, APP-KPI (p=0.007), APP770 (p=0.004), PS-1 (p=0.004), LRP (p=0.003), apoE (p=0.0002) and GFAP (p<0.0001) mRNA levels all increased in AD, and there was a shift from APP695 (a neuronal isoform) towards KPI containing isoforms that are present in glia as well. APP-KPI mRNA levels correlated with soluble APPalpha-KPI protein (sAPPalpha-KPI) levels measured by ELISA (tau=0.33, p=0.015 by Kendall's rank correlation); in turn, soluble APPalpha-KPI protein levels positively correlated with Tris-extractable, soluble Abeta40 (p=0.046) and 42 levels (p=0.007). The ratio of soluble APPalpha-KPI protein levels to total APP protein increased in AD, and also correlated with GFAP protein levels in AD. These results suggest that altered transcription of APP in AD is proportionately associated with Abeta peptide, may occur in the context of gliosis, and may contribute to Abeta deposition in sporadic AD.

Coordinated expression of caspase 8, 3 and 7 mRNA in temporal cortex of Alzheimer disease: relationship to formic acid extractable abeta42 levels.

Recent studies support the hypothesis that Alzheimer disease (AD)-associated amyloid-beta protein (Abeta) may induce apoptosis mediated by a caspase cascade. To assess whether mRNA levels of caspase-3, 7, 8 and 9 change in AD brain, and whether these changes correlate with neurofibrillary tangles, Abeta40 or Abeta42 protein levels or senile plaques, 25 AD and 21 non-demented control brains were examined. Elevated mRNA levels of caspases-7 and 8 measured by a quantitative PCR method were observed in the AD temporal neocortex as compared to the control brains. No significant differences were noticed in levels of caspases-3 or 9 between AD and control brains. Multiple regression analysis demonstrated that, within subjects, the mRNA levels of caspase-8 strongly correlated with both caspse-3 and caspase-7 independently of postmortem interval. Further, there was a strong positive correlation of caspase-8 levels with formic acid extractable Abeta42 levels. Our results suggest that the transcriptional activation of key components of the apoptotic cascade correlates with accumulation of Abeta 42. Thus, a principal caspase pathway from caspase-8 to caspase-3 and/or 7 may contribute to neuron loss in AD brain.

Beta-secretase protein and activity are increased in the neocortex in Alzheimer disease.

CONTEXT: Amyloid plaques, a major pathological feature of Alzheimer disease (AD), are composed of an internal fragment of amyloid precursor protein (APP): the 4-kd amyloid-beta protein (Abeta). The metabolic processing of APP that results in Abeta formation requires 2 enzymatic cleavage events, a gamma-secretase cleavage dependent on presenilin, and a beta-secretase cleavage by the aspartyl protease beta-site APP-cleaving enzyme (BACE). OBJECTIVE: To test the hypothesis that BACE protein and activity are increased in regions of the brain that develop amyloid plaques in AD. METHODS: We developed an antibody capture system to measure BACE protein level and BACE-specific beta-secretase activity in frontal, temporal, and cerebellar brain homogenates from 61 brains with AD and 33 control brains. RESULTS: In the brains with AD, BACE activity and protein were significantly increased (P<.001). Enzymatic activity increased by 63% in the temporal neocortex (P =.007) and 13% in the frontal neocortex (P =.003) in brains with AD, but not in the cerebellar cortex. Activity in the temporal neocortex increased with the duration of AD (P =.008) but did not correlate with enzyme-linked immunosorbent assay measures of insoluble Abeta in brains with AD. Protein level was increased by 14% in the frontal cortex of brains with AD (P =.004), with a trend toward a 15% increase in BACE protein in the temporal cortex (P =.07) and no difference in the cerebellar cortex. Immunohistochemical analysis demonstrated that BACE immunoreactivity in the brain was predominantly neuronal and was found in tangle-bearing neurons in AD. CONCLUSIONS: The BACE protein and activity levels are increased in brain regions affected by amyloid deposition and remain increased despite significant neuronal and synaptic loss in AD.

Age but not diagnosis is the main predictor of plasma amyloid beta-protein levels.

BACKGROUND: Plasma amyloid beta-protein Abeta42 levels are increased in patients with familial Alzheimer disease (AD) mutations, and high levels reportedly identify individuals at risk to develop AD. OBJECTIVES: To determine whether there are characteristic changes in plasma Abeta40 and Abeta42 levels in sporadic AD, and to examine the relationship of plasma Abeta measures with clinical, demographic, and genetic variables in a prospectively characterized outpatient clinic population. PATIENTS: A total of 371 outpatients with sporadic AD (n = 146), mild cognitive impairment (n = 37), or Parkinson disease (n = 96) and nondemented control cases (n = 92). METHODS: We collected plasma samples and determined Abeta40 and Abeta42 levels by sandwich enzyme-linked immunosorbent assay with the use of the capture antibody BNT77 (anti-Abeta11-28) and the detector antibodies horseradish peroxidase-linked BA27 (anti-Abeta40) and BC05 (anti-Abeta42). RESULTS: Mean Abeta40 and Abeta42 levels increased significantly with age in each diagnostic group. When covaried for age, mean plasma levels of Abeta40 and Abeta42 did not differ significantly among the 4 diagnostic groups. Within the mild cognitive impairment and AD groups, Abeta40 and Abeta42 levels did not correlate with duration of memory impairment or with cognitive test scores. The Abeta measures were not influenced by family history of AD, apolipoprotein E genotype, or current medication use of cholinesterase inhibitors, vitamin E, statins, nonsteroidal anti-inflammatory drugs, or estrogen. CONCLUSIONS: Plasma Abeta measures increase with age, but, in contrast to reports on familial AD, plasma Abeta measures were neither sensitive nor specific for the clinical diagnosis of mild cognitive impairment or sporadic AD.

Ameliorative effects of a non-competitive BACE1 inhibitor TAK-070 on Aß peptide levels and impaired learning behavior in aged rats.

We examined the effects of TAK-070, a novel non-competitive ß-secretase (BACE1) inhibitor, on the levels of Aß peptides and behavioral deficits in rats. TAK-070 reduced soluble Aß40 and Aß42 levels of the cerebral cortex in a time- and dose-dependent manner in young rats. We found that the insoluble Aß42 content increased significantly with aging from 22 months old without changing Aß40 content. TAK-070 normalized the Aß42 levels to those in young rats when they were fed chow containing TAK-070 starting at 19 months old for 6.5 months. Repeated administration of TAK-070 to aged rats for 2 weeks ameliorated the impaired spatial learning in the Morris water maze task and reduced the levels of soluble and insoluble Aß peptides at doses of 0.3-1mg/kg, (p.o.). Interestingly, TAK-070 significantly recovered the reduced brain synaptophysin levels in aged rats to those in young rats. Our findings support the idea that partial inhibition of BACE1 by TAK-070 exerts symptomatic as well as disease-modifying effects for the treatment of Alzheimer's disease.

Plasma amyloid beta-protein and C-reactive protein in relation to the rate of progression of Alzheimer disease.

OBJECTIVE: To examine whether plasma markers of amyloid precursor protein metabolism (amyloid beta-protein ending in Val-40 [Abeta40] and Ala-42 [Abeta42]), inflammation (high-sensitivity C-reactive protein), and folic acid metabolism (folic acid, vitamin B(12), and total homocysteine levels) are associated with the rate of cognitive and functional decline in persons with Alzheimer disease. DESIGN: Longitudinal study across a mean (SD) of 4.2 (2.6) years with assessments at approximately 6- to 12-month intervals. SETTING: Outpatient care. PATIENTS: A cohort of 122 patients having a clinical diagnosis of probable Alzheimer disease, each with at least 2 assessments across time. MAIN OUTCOME MEASURES: Scores on the cognitive Information-Memory-Concentration subscale of the Blessed Dementia Scale and the functional Weintraub Activities of Daily Living Scale. RESULTS: Low plasma levels of Abeta40, Abeta42, and high-sensitivity C-reactive protein were associated with a significantly more rapid cognitive decline, as indexed using the Blessed Dementia Scale, than were high levels. Low levels of Abeta42 and high-sensitivity C-reactive protein were significantly associated with more rapid functional decline on the Weintraub Activities of Daily Living Scale than were high levels. These plasma markers contributed about 5% to 12% of the variance accounted for on the Blessed Dementia Scale and the Activities of Daily Living Scale by fixed-effects predictors. Measures of folic acid metabolism were not associated with changes on either the Blessed Dementia Scale or the Activities of Daily Living Scale. CONCLUSIONS: Plasma markers of amyloid precursor protein metabolism and C-reactive protein may be associated with the rate of cognitive and functional decline in patients with Alzheimer disease.

Passive immunization of the Abeta42(43) C-terminal-specific antibody BC05 in a mouse model of Alzheimer's disease.

BACKGROUND: Over the past few years, amyloid beta protein (Abeta) vaccination has become one of the most effective treatments for Alzheimer's disease. However, the appearance of severe side effects during clinical trials has highlighted the need for improved safety and efficacy. Although antibodies directed against the amino (N)-termini of Abeta are highly effective for passive immunization, a substantial risk of inducing cerebral hemorrhage has been documented. OBJECTIVE: We investigated the effect of the administration of BC05, which was the first antibody developed against the carboxyl (C)-termini of Abeta42(43), on the clearance of brain Abeta42(43). METHOD: The BC05 antibody was injected into the peritoneal cavity of Tg2576 transgenic mice expressing betaAPP(KM670/671NL) once a week from 3 to 12 months of age. RESULTS: BC05 caused a selective 44-fold increase in plasma Abeta42(43) and a significant increase in brain soluble Abeta42(43), showing a 156% difference. Brain insoluble Abeta40 and Abeta42(43) levels were decreased by 27.3 and 31.5%, respectively. A reduction in the number of BAN50-labeled plaques was observed. CONCLUSIONS: BC05 might render Abeta42(43) soluble within the brain and inhibit the insoluble deposition of Abeta40 and Abeta42(43). By analyzing the mechanism of the elevation of soluble Abeta42(43) after passive immunization of BC05, safer and more effective methods of immunotherapy for Alzheimer's disease might be developed.

Decreased levels of BDNF protein in Alzheimer temporal cortex are independent of BDNF polymorphisms.

Levels of brain-derived neurotrophic factor (BDNF) are reduced in specific brain regions in Alzheimer's disease (AD) and BDNF gene polymorphisms have been suggested to influence AD risk, hippocampal function, and memory. We investigated whether the polymorphisms at the BDNF 196 and 270 loci were associated with AD in a clinical and neuropathological cohort of 116 AD cases and 77 control subjects. To determine how BDNF protein levels relate to BDNF polymorphisms and AD pathology, we also measured BDNF in temporal association cortex, frontal association cortex, and cerebellum in 57 of the AD and 21 control cases. BDNF protein levels in temporal neocortex of the AD brains were reduced by 33% compared to control brains, whereas levels were unchanged in frontal and cerebellar cortex. The BDNF genotypes were not significantly associated with a diagnosis of AD, although the BDNF 270 C allele was slightly overrepresented among carriers of the APOEepsilon4 allele. Moreover, BDNF protein levels did not differ between the various BDNF genotypes and alleles. Neuropathologically, the loss of BDNF in AD showed a weak correlation with accumulation of neuritic amyloid plaques and loss of the neuronal/synaptic marker synaptophysin. The results suggest that the investigated BDNF polymorphisms are neither robust genetic risk factors nor determinants of BDNF protein levels in AD.

Induction of the cholesterol transporter ABCA1 in central nervous system cells by liver X receptor agonists increases secreted Abeta levels.

The expression, function, and regulation of the cholesterol efflux molecule, ABCA1, has been extensively examined in peripheral tissues but only poorly studied in the brain. Brain cholesterol metabolism is of interest because several lines of evidence suggest that elevated cholesterol increases the risk of Alzheimer's disease. We found a largely neuronal expression of ABCA1 in normal rat brain by in situ hybridization. ABCA1 message was dramatically up-regulated in neurons and glia in areas of damage by hippocampal AMPA lesion after 3-7 days. Immunoblot analysis demonstrated ABCA1 protein in cultured neuronal and glial cells, and expression was induced by ligands of the nuclear hormone receptors of the retinoid X receptor and liver X receptor family. ABCA1 was induced by treatment with retinoic acid and several oxysterols, including 22(R)-hydroxycholesterol and 24-hydroxycholesterol. Expression of an ABCA1-green fluorescent protein construct in neuroblastoma cells demonstrated fluorescence in perinuclear compartments and on the plasma membrane. Because the Abeta peptide is important in Alzheimer's disease pathogenesis, we examined whether ABCA1 induction altered Abeta levels. Treatment of neuroblastoma cells with retinoic acid and 22(R)-hydroxycholesterol caused significant increases in secreted Abeta40 (29%) and Abeta42 (65%). Treatment with a nonsteroidal liver X receptor ligand, TO-901317, similarly increased levels of secreted Abeta40 (25%) and Abeta42 (126%). The increase in secreted Abeta levels was reduced by RNAi blocking of ABCA1 expression. These data suggest that the cholesterol efflux molecule ABCA1 may also be involved in the secretion of the membrane-associated molecule, Abeta.

Abeta species, including IsoAsp23 Abeta, in Iowa-type familial cerebral amyloid angiopathy.

Mutations within the Abeta sequence of the AbetaPP gene are associated with familial forms of cerebral amyloid angiopathy (CAA). One mutation, Abeta D23N, was identified in a family in Iowa with a clinical history of early-onset dementia. We analyzed the pattern of Abeta deposition in the hippocampus of an individual with Iowa CAA. In addition to strong amyloid angiopathy, we found unusual diffuse Abeta deposits in the CA4, and in the parenchyma near amyloid-laden vessels. ELISA of cortical brain extracts showed that Abeta40 was nearly 20-fold higher than Abeta42, in both soluble and insoluble fractions. We identified an Abeta antibody that recognized wild-type Abeta but not Iowa Abeta. With this antibody, we found that wild-type Abeta was present in the Abeta deposits, but limited to the strongest deposits in the cerebrovasculature. Previous in vitro studies suggested that the presence of an asparagine at position 23 of Abeta favored formation of an isoAsp residue, which was associated with increased Abeta fibrillogenesis. Using isoAsp-specific antibodies in immunohistochemical studies, we examined the distribution of isoAsp Abeta in the Iowa brain. IsoAsp7 Abeta was present in both the parenchymal and vascular deposits, whereas isoAsp23 Abeta was present only in vascular deposits. These data suggest that alteration of Abeta Asn23 to isoAsp may be an important determinant in the deposition of Abeta in cerebral blood vessels.

Beta-secretase activity increases with aging in human, monkey, and mouse brain.

Amyloid beta protein (A beta) accumulates in the brains of aging humans, amyloid precursor protein (APP) transgenic mouse lines, and rhesus monkeys. We tested the hypothesis that aging was associated with increased activity of the beta-site amyloid precursor protein cleaving enzyme (beta-secretase, BACE) in brain. We evaluated BACE activity, BACE protein, and formic acid-extractable A beta levels in cohorts of young (4 months old) and old (14 to 18 months old) nontransgenic mice (n = 16) and Tg2576 APP transgenic mice (n = 17), young (4.4 to 12.7 years old) and old (20.9 to 30.4 years old) rhesus monkeys (n = 17), and a wide age range (18 to 92 years old) of nondemented human brains (n = 25). Aging was associated with increased brain A beta levels in each cohort. Furthermore BACE activity increased significantly with age in mouse, monkey, and human brains, independent of brain region. BACE protein levels, however, were unchanged with age. BACE activity correlated with formic acid-extractable A beta levels in transgenic mouse, nontransgenic mouse, and human cortex, but not in monkey brain. These data suggest that an age-related increase of BACE activity contributes to the increased production and accumulation of brain A beta, and potentially predisposes to Alzheimer's disease in humans.

Notch1 competes with the amyloid precursor protein for gamma-secretase and down-regulates presenilin-1 gene expression.

Presenilin 1 (PS1) is a critical component of the gamma-secretase complex, which is involved in the cleavage of several substrates including the amyloid precursor protein (APP) and Notch1. Based on the fact that APP and Notch are processed by the same gamma-secretase, we postulated that APP and Notch compete for the enzyme activity. In this report, we examined the interactions between APP, Notch, and PS1 using the direct gamma-secretase substrates, Notch 1 Delta extracellular domain (N1DeltaEC) and APP carboxyl-terminal fragment of 99 amino acids, and measured the effects on amyloid-beta protein production and Notch signaling, respectively. Additionally, we tested the hypothesis that downstream effects on PS1 expression may coexist with the competition phenomenon. We observed significant competition between Notch and APP for gamma-secretase activity; transfection with either of two direct substrates of gamma-secretase led to a reduction in the gamma-cleaved products, Notch intracellular domain or amyloid-beta protein. In addition, however, we found that activation of the Notch signaling pathway, by either N1 Delta EC or Notch intracellular domain, induced down-regulation of PS1 gene expression. This finding suggests that Notch activation directly engages gamma-secretase and subsequently leads to diminished PS1 expression, suggesting a complex set of feedback interactions following Notch activation.

Demonstration by FRET of BACE interaction with the amyloid precursor protein at the cell surface and in early endosomes.

Amyloid-beta peptide, which accumulates in senile plaques in Alzheimer's disease, is derived from the amyloid precursor protein (APP) by proteolytic processing. beta-secretase (Asp2), which cleaves APP at the N-terminus of amyloid-beta, has recently been identified to be the protease BACE. In the present study, we examined the subcellular localization of interactions between APP and BACE by using both double immunofluorescence and a fluorescence resonance energy transfer (FRET) approach. Cell surface APP and BACE, studied by using antibodies directed against their ectodomains in living H4 neuroglioma cells co-transfected with APP and BACE, showed exquisite co-localization and demonstrated a very close interaction by FRET analysis. The majority of cell surface APP and BACE were internalized after 15 minutes, but they remained strongly co-localized together in the early endosomal compartment, where FRET analysis demonstrated a continued close interaction. By contrast, at later timepoints, almost no co-localization or FRET was observed in lysosomal compartments. To determine whether the APP-BACE interaction on cell surface and endosomes contributed to amyloid-beta synthesis, we labeled cell surface APP and demonstrated detectable levels of labeled amyloid-beta within 30 minutes. APP-Swedish mutant protein enhanced amyloid-beta synthesis from cell surface APP, consistent with the observation that it is a better BACE substrate than wild-type APP. Taken together, these data confirm a close APP-BACE interaction in early endosomes, and highlight the cell surface as an additional potential site of APP-BACE interaction.

APOE epsilon 3/ epsilon 4 heterozygotes have an elevated proportion of apolipoprotein E4 in cerebrospinal fluid relative to plasma, independent of Alzheimer's disease diagnosis.

Inheritance of the apolipoprotein E (APOE) epsilon 4 allele is associated with an increased risk of Alzheimer's disease (AD). However, the risk of AD in APOE epsilon 3/ epsilon 4 heterozygotes is variable. We tested the hypothesis that the risk of AD in APOE epsilon 3/ epsilon 4 heterozygotes was linked to the relative levels of expression of apoE4 versus apoE3 protein. We measured the apoE4 isoform and total apoE using two specific enzyme-linked immunosorbent assay (ELISA) kits in three cohorts of plasma samples and two cohorts of cerebrospinal fluid samples from AD, mild cognitive impairment, and control subjects. The apoE4 ELISAs were specific as they did not detect apoE in APOE epsilon 3/epsilon 3 homozygotes and were comparable to the total apoE ELISAs in APOE epsilon 4/ epsilon 4 homozygotes. In APOE epsilon 3/ epsilon 4 individuals, the ratio of apoE4 to total apoE levels was 30-40% in plasma, suggesting a decreased production or an increased metabolism of apoE4 compared to apoE3. Surprisingly, the ratio in the CSF was reversed, with apoE4 accounting for 60-70% of the total apoE. The proportion of apoE4 in these cases did not vary by diagnosis, age of onset, or duration of AD. We conclude that the proportion of apoE4 in plasma is not predictive of AD risk in APOE epsilon 3/epsilon 4 individuals. However, the greater proportion of apoE4 in the cerebrospinal fluid suggests differential production or metabolism of the protein in the central nervous system (CNS), with the apoE4 isoform dominating.