N-cadherin: A diagnostic marker to help discriminate primary liver carcinomas from extrahepatic carcinomas.

Distinguishing primary liver cancer (PLC), namely hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (iCCA), from liver metastases is of crucial clinical importance. Histopathology remains the gold standard, but differential diagnosis may be challenging. While absent in most epithelial, the expression of the adherens junction glycoprotein N-cadherin is commonly restricted to neural and mesenchymal cells, or carcinoma cells that undergo the phenomenon of epithelial-to-mesenchymal transition (EMT). However, we recently established N- and E-cadherin expression as hallmarks of normal hepatocytes and cholangiocytes, which are also preserved in HCC and iCCA. Therefore, we hypothesized that E- and/or N-cadherin may distinguish between carcinoma derived from the liver vs carcinoma of other origins. We comprehensively evaluated E- and N-cadherin in 3359 different tumors in a multicenter study using immunohistochemistry and compared our results with previously published 882 cases of PLC, including 570 HCC and 312 iCCA. Most carcinomas showed strong positivity for E-cadherin. Strong N-cadherin positivity was present in HCC and iCCA. However, except for clear cell renal cell carcinoma (23.6% of cases) and thyroid cancer (29.2%), N-cadherin was only in some instances faintly expressed in adenocarcinomas of the gastrointestinal tract (0%-0.5%), lung (7.1%), pancreas (3.9%), gynecological organs (0%-7.4%), breast (2.2%) as well as in urothelial (9.4%) and squamous cell carcinoma (0%-5.6%). As expected, N-cadherin was detected in neuroendocrine tumors (25%-75%), malignant melanoma (46.2%) and malignant mesothelioma (41%). In conclusion, N-cadherin is a useful marker for the distinction of PLC vs liver metastases of extrahepatic carcinomas (P < .01).

Etiology-independent activation of the LTß-LTßR-RELB axis drives aggressiveness and predicts poor prognosis in HCC.

BACKGROUND AND AIMS: HCC is the most common primary liver tumor, with an increasing incidence worldwide. HCC is a heterogeneous malignancy and usually develops in a chronically injured liver. The NF-κB signaling network consists of a canonical and a noncanonical branch. Activation of canonical NF-κB in HCC is documented. However, a functional and clinically relevant role of noncanonical NF-κB and its downstream effectors is not established. APPROACH AND RESULTS: Four human HCC cohorts (total n = 1462) and 4 mouse HCC models were assessed for expression and localization of NF-κB signaling components and activating ligands. In vitro , NF-κB signaling, proliferation, and cell death were measured, proving a pro-proliferative role of v-rel avian reticuloendotheliosis viral oncogene homolog B (RELB) activated by means of NF-κB-inducing kinase. In vivo , lymphotoxin beta was identified as the predominant inducer of RELB activation. Importantly, hepatocyte-specific RELB knockout in a murine HCC model led to a lower incidence compared to controls and lower maximal tumor diameters. In silico , RELB activity and RELB-directed transcriptomics were validated on the The Cancer Genome Atlas HCC cohort using inferred protein activity and Gene Set Enrichment Analysis. In RELB-active HCC, pathways mediating proliferation were significantly activated. In contrast to v-rel avian reticuloendotheliosis viral oncogene homolog A, nuclear enrichment of noncanonical RELB expression identified patients with a poor prognosis in an etiology-independent manner. Moreover, RELB activation was associated with malignant features metastasis and recurrence. CONCLUSIONS: This study demonstrates a prognostically relevant, etiology-independent, and cross-species consistent activation of a lymphotoxin beta/LTßR/RELB axis in hepatocarcinogenesis. These observations may harbor broad implications for HCC, including possible clinical exploitation.

Microvascular invasion of hepatocellular carcinoma predicts microvascular invasion of its recurrence: potential implications for salvage liver transplantation?

Background: Microvascular invasion (MVI) can only be assessed on a full surgical specimen. We aimed at evaluating, whether the histology of the primary tumor is predictive of MVI in a hepatocellular carcinoma (HCC) recurrence. Methods: Patients, who underwent liver resection or orthotopic liver transplantation (OLT) for recurrent HCC from January 2001 until June 2018 were eligible for this retrospective analysis. Resected specimens were evaluated for HCC subtype/morphology, vessels encapsulating tumor clusters (VETC)-pattern and MVI. Dichotomous parameters were analyzed using χ2-test and ϕ-values, with P values <0.05 being considered significant. Results: Of 230 HCC recurrences, 37 (16.1%) underwent repeated liver resection (n=22) or OLT (n=15). Of these, 67.6% initially exceeded the Milan criteria. MVI correlated Milan criteria (P=0.005), tumor size (P=0.015) and VETC-pattern (P=0.034) in the primary specimen. The recurrences shared many features of the primary HCC such as tumor grade (P=0.002), VETC-pattern (P=0.035), and MVI (P=0.046). In recurrences, however, only the concordance with the Milan criteria correlated with MVI (P=0.018). No patient without MVI in the primary HCC revealed MVI on early recurrence (<2 years) (P=0.035). Conclusions: HCC recurrences share many biological features of the primary tumor. Moreover, early recurrences of MVI-negative HCC never revealed MVI. This finding offers novel concepts, e.g., patient selection for salvage OLT.

N-Cadherin Distinguishes Intrahepatic Cholangiocarcinoma from Liver Metastases of Ductal Adenocarcinoma of the Pancreas.

Carcinomas of the pancreatobiliary system confer an especially unfavorable prognosis. The differential diagnosis of intrahepatic cholangiocarcinoma (iCCA) and its subtypes versus liver metastasis of ductal adenocarcinoma of the pancreas (PDAC) is clinically important to allow the best possible therapy. We could previously show that E-cadherin and N-cadherin, transmembrane glycoproteins of adherens junctions, are characteristic features of hepatocytes and cholangiocytes. We therefore analyzed E-cadherin and N-cadherin in the embryonally related epithelia of the bile duct and pancreas, as well as in 312 iCCAs, 513 carcinomas of the extrahepatic bile ducts, 228 gallbladder carcinomas, 131 PDACs, and precursor lesions, with immunohistochemistry combined with image analysis, fluorescence microscopy, and immunoblots. In the physiological liver, N-cadherin colocalizes with E-cadherin in small intrahepatic bile ducts, whereas larger bile ducts and pancreatic ducts are positive for E-cadherin but contain decreasing amounts of N-cadherin. N-cadherin was highly expressed in most iCCAs, whereas in PDACs, N-cadherin was negative or only faintly expressed. E- and N-cadherin expression in tumors of the pancreaticobiliary tract recapitulate their expression in their normal tissue counterparts. N-cadherin is a helpful marker for the differential diagnosis between iCCA and PDAC, with a specificity of 96% and a sensitivity of 67% for small duct iCCAs and 50% for large duct iCCAs.

Integrative Analysis of Intrahepatic Cholangiocarcinoma Subtypes for Improved Patient Stratification: Clinical, Pathological, and Radiological Considerations.

Intrahepatic cholangiocarcinomas (iCCAs) may be subdivided into large and small duct types that differ in etiology, molecular alterations, therapy, and prognosis. Therefore, the optimal iCCA subtyping is crucial for the best possible patient outcome. In our study, we analyzed 148 small and 84 large duct iCCAs regarding their clinical, radiological, histological, and immunohistochemical features. Only 8% of small duct iCCAs, but 27% of large duct iCCAs, presented with initial jaundice. Ductal tumor growth pattern and biliary obstruction were significant radiological findings in 33% and 48% of large duct iCCAs, respectively. Biliary epithelial neoplasia and intraductal papillary neoplasms of the bile duct were detected exclusively in large duct type iCCAs. Other distinctive histological features were mucin formation and periductal-infiltrating growth pattern. Immunohistochemical staining against CK20, CA19-9, EMA, CD56, N-cadherin, and CRP could help distinguish between the subtypes. To summarize, correct subtyping of iCCA requires an interplay of several factors. While the diagnosis of a precursor lesion, evidence of mucin, or a periductal-infiltrating growth pattern indicates the diagnosis of a large duct type, in their absence, several other criteria of diagnosis need to be combined.

Dual roles of B lymphocytes in mouse models of diet-induced nonalcoholic fatty liver disease.

BACKGROUND AND AIMS: Growing evidence suggests an important role of B cells in the development of NAFLD. However, a detailed functional analysis of B cell subsets in NAFLD pathogenesis is lacking. APPROACH AND RESULTS: In wild-type mice, 21 weeks of high fat diet (HFD) feeding resulted in NAFLD with massive macrovesicular steatosis, modest hepatic and adipose tissue inflammation, insulin resistance, and incipient fibrosis. Remarkably, Bnull (JHT) mice were partially protected whereas B cell harboring but antibody-deficient IgMi mice were completely protected from the development of hepatic steatosis, inflammation, and fibrosis. The common feature of JHT and IgMi mice is that they do not secrete antibodies, whereas HFD feeding in wild-type mice led to increased levels of serum IgG2c. Whereas JHT mice have no B cells at all, regulatory B cells were found in the liver of both wild-type and IgMi mice. HFD reduced the number of regulatory B cells and IL-10 production in the liver of wild-type mice, whereas these increased in IgMi mice. Livers of patients with advanced liver fibrosis showed abundant deposition of IgG and stromal B cells and low numbers of IL-10 expressing cells, compatible with our experimental data. CONCLUSIONS: B lymphocytes have both detrimental and protective effects in HFD-induced NAFLD. The lack of secreted pathogenic antibodies protects partially from NAFLD, whereas the presence of certain B cell subsets provides additional protection. IL-10-producing regulatory B cells may represent such a protective B cell subset.

Epigenetic modifications precede molecular alterations and drive human hepatocarcinogenesis.

Development of primary liver cancer is a multistage process. Detailed understanding of sequential epigenetic alterations is largely missing. Here, we performed Infinium Human Methylation 450k BeadChips and RNA-Seq analyses for genome-wide methylome and transcriptome profiling of cirrhotic liver (n = 7), low- (n = 4) and high-grade (n = 9) dysplastic lesions, and early (n = 5) and progressed (n = 3) hepatocellular carcinomas (HCC) synchronously detected in 8 patients with HCC with chronic hepatitis B infection. Integrative analyses of epigenetically driven molecular changes were identified and validated in 2 independent cohorts comprising 887 HCCs. Mitochondrial DNA sequencing was further employed for clonality analyses, indicating multiclonal origin in the majority of investigated HCCs. Alterations in DNA methylation progressively increased from liver cirrhosis (CL) to dysplastic lesions and reached a maximum in early HCCs. Associated early alterations identified by Ingenuity Pathway Analysis (IPA) involved apoptosis, immune regulation, and stemness pathways, while late changes centered on cell survival, proliferation, and invasion. We further validated 23 putative epidrivers with concomitant expression changes and associated with overall survival. Functionally, Striatin 4 (STRN4) was demonstrated to be epigenetically regulated, and inhibition of STRN4 significantly suppressed tumorigenicity of HCC cell lines. Overall, application of integrative genomic analyses defines epigenetic driver alterations and provides promising targets for potentially novel therapeutic approaches.

Cerebral angiogenesis ameliorates pathological disorders in Nemo-deficient mice with small-vessel disease.

Cerebral small-vessel diseases (SVDs) often follow a progressive course. Little is known about the function of angiogenesis, which potentially induces regression of SVDs. Here, we investigated angiogenesis in a mouse model of incontinentia pigmenti (IP), a genetic disease comprising features of SVD. IP is caused by inactivating mutations of Nemo, the essential component of NF-κB signaling. When deleting Nemo in the majority of brain endothelial cells (NemobeKO mice), the transcriptional profile of vessels indicated cell proliferation. Brain endothelial cells expressed Ki67 and showed signs of DNA synthesis. In addition to cell proliferation, we observed sprouting and intussusceptive angiogenesis in NemobeKO mice. Angiogenesis occurred in all segments of the vasculature and in proximity to vessel rarefaction and tissue hypoxia. Apparently, NEMO was required for productive angiogenesis because endothelial cells that had escaped Nemo inactivation showed a higher proliferation rate than Nemo-deficient cells. Therefore, newborn endothelial cells were particularly vulnerable to ongoing recombination. When we interfered with productive angiogenesis by inducing ongoing ablation of Nemo, mice did not recover from IP manifestations but rather showed severe functional deficits. In summary, the data demonstrate that angiogenesis is present in this model of SVD and suggest that it may counterbalance the loss of vessels.

Intra-arterial Injection of Lidocaine as a Cell Sensitizer during Irreversible Electroporation.

PURPOSE: To investigate whether intra-arterial injection of lidocaine enhances irreversible electroporation (IRE) in a liver model. MATERIALS AND METHODS: Conventional IRE (C-IRE) and lidocaine-enhanced IRE (L-IRE) were performed in 8 pig livers. Protocol 1 (tip exposure and electrode distance of 2.0 cm each) and protocol 2 (increased tip exposure and electrode distance 2.5 cm each) were used. Animals were sacrificed 3 hours after IRE. Study goals included electrical tissue properties (eg, current, conductivity) during IRE, geometry of IRE zones analyzed using computed tomography and magnetic resonance imaging (eg, volume and sphericity index), degree of acute liver damage, and irreversible cell death analyzed using microscopy (hematoxylin and eosin staining and terminal deoxynucleotidyl transferase deoxyuridine 5-triphosphate nick end labeling). Statistical comparisons were performed using the paired t test and Wilcoxon test. RESULTS: All treatments were performed without adverse events. Electrical tissue properties were not significantly different between C-IRE and L-IRE. For protocol 1, the diameter of the largest sphere within the IRE zone was significantly larger for L-IRE than for C-IRE (25.0 ± 4.7 mm vs 18.4 ± 3.1 mm [P = .013]). For protocol 2, the volume of IRE zone was significantly larger for L-IRE compared with C-IRE (46.0 ± 5.4 cm3 vs 22.6 ± 6.4 cm3 [P = .018]), as well as the diameter of the largest sphere within the IRE zone (27.1 ± 2.2 mm vs 19.8 ± 2.3 mm [P = .020]). For protocol 1, a significantly higher degree of irreversible cell death was noted for L-IRE than for C-IRE (1.8 ± 1.0 vs 0.8 ± 1.0 [P = .046]). CONCLUSIONS: Intra-arterial injection of lidocaine can enhance IRE in terms of larger IRE zones and an increase of irreversible cell death.

Gene therapy decreases seizures in a model of Incontinentia pigmenti.

OBJECTIVE: Incontinentia pigmenti (IP) is a genetic disease leading to severe neurological symptoms, such as epileptic seizures, but no specific treatment is available. IP is caused by pathogenic variants that inactivate the Nemo gene. Replacing Nemo through gene therapy might provide therapeutic benefits. METHODS: In a mouse model of IP, we administered a single intravenous dose of the adeno-associated virus (AAV) vector, AAV-BR1-CAG-NEMO, delivering the Nemo gene to the brain endothelium. Spontaneous epileptic seizures and the integrity of the blood-brain barrier (BBB) were monitored. RESULTS: The endothelium-targeted gene therapy improved the integrity of the BBB. In parallel, it reduced the incidence of seizures and delayed their occurrence. Neonate mice intravenously injected with the AAV-BR1-CAG-NEMO vector developed no hepatocellular carcinoma or other major adverse effects 11 months after vector injection, demonstrating that the vector has a favorable safety profile. INTERPRETATION: The data show that the BBB is a target of antiepileptic treatment and, more specifically, provide evidence for the therapeutic benefit of a brain endothelial-targeted gene therapy in IP. Ann Neurol 2017;82:93-104.

A brain microvasculature endothelial cell-specific viral vector with the potential to treat neurovascular and neurological diseases.

Gene therapy critically relies on vectors that combine high transduction efficiency with a high degree of target specificity and that can be administered through a safe intravenous route. The lack of suitable vectors, especially for gene therapy of brain disorders, represents a major obstacle. Therefore, we applied an in vivo screening system of random ligand libraries displayed on adeno-associated viral capsids to select brain-targeted vectors for the treatment of neurovascular diseases. We identified a capsid variant showing an unprecedented degree of specificity and long-lasting transduction efficiency for brain microvasculature endothelial cells as the primary target of selection. A therapeutic vector based on this selected viral capsid was used to markedly attenuate the severe cerebrovascular pathology of mice with incontinentia pigmenti after a single intravenous injection. Furthermore, the versatility of this selection system will make it possible to select ligands for additional in vivo targets without requiring previous identification of potential target-specific receptors.

Brain endothelial TAK1 and NEMO safeguard the neurovascular unit.

Inactivating mutations of the NF-κB essential modulator (NEMO), a key component of NF-κB signaling, cause the genetic disease incontinentia pigmenti (IP). This leads to severe neurological symptoms, but the mechanisms underlying brain involvement were unclear. Here, we show that selectively deleting Nemo or the upstream kinase Tak1 in brain endothelial cells resulted in death of endothelial cells, a rarefaction of brain microvessels, cerebral hypoperfusion, a disrupted blood-brain barrier (BBB), and epileptic seizures. TAK1 and NEMO protected the BBB by activating the transcription factor NF-κB and stabilizing the tight junction protein occludin. They also prevented brain endothelial cell death in a NF-κB-independent manner by reducing oxidative damage. Our data identify crucial functions of inflammatory TAK1-NEMO signaling in protecting the brain endothelium and maintaining normal brain function, thus explaining the neurological symptoms associated with IP.

Deletion of prostaglandin E2 synthesizing enzymes in brain endothelial cells attenuates inflammatory fever.

Fever is a hallmark of inflammatory and infectious diseases. The febrile response is triggered by prostaglandin E2 synthesis mediated by induced expression of the enzymes cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase 1 (mPGES-1). The cellular source for pyrogenic PGE2 remains a subject of debate; several hypotheses have been forwarded, including immune cells in the periphery and in the brain, as well as the brain endothelium. Here we generated mice with selective deletion of COX-2 and mPGES1 in brain endothelial cells. These mice displayed strongly attenuated febrile responses to peripheral immune challenge. In contrast, inflammation-induced hypoactivity was unaffected, demonstrating the physiological selectivity of the response to the targeted gene deletions. These findings demonstrate that PGE2 synthesis in brain endothelial cells is critical for inflammation-induced fever.

The ß-hydroxybutyrate receptor HCA2 activates a neuroprotective subset of macrophages.

The ketone body ß-hydroxybutyrate (BHB) is an endogenous factor protecting against stroke and neurodegenerative diseases, but its mode of action is unclear. Here we show in a stroke model that the hydroxy-carboxylic acid receptor 2 (HCA2, GPR109A) is required for the neuroprotective effect of BHB and a ketogenic diet, as this effect is lost in Hca2(-/-) mice. We further demonstrate that nicotinic acid, a clinically used HCA2 agonist, reduces infarct size via a HCA2-mediated mechanism, and that noninflammatory Ly-6C(Lo) monocytes and/or macrophages infiltrating the ischemic brain also express HCA2. Using cell ablation and chimeric mice, we demonstrate that HCA2 on monocytes and/or macrophages is required for the protective effect of nicotinic acid. The activation of HCA2 induces a neuroprotective phenotype of monocytes and/or macrophages that depends on PGD2 production by COX1 and the haematopoietic PGD2 synthase. Our data suggest that HCA2 activation by dietary or pharmacological means instructs Ly-6C(Lo) monocytes and/or macrophages to deliver a neuroprotective signal to the brain.

TAK1 inhibition for treatment of cerebral ischemia.

TGFß-activated kinase 1 (TAK1), a MAP3 kinase, is involved in at least five signaling cascades that modulate ischemic brain damage. Inhibition of TAK1 may therefore be an efficient way to interfere with multiple mechanisms in ischemic stroke. Indeed, a recent publication in Experimental Neurology confirmed that TAK1 inhibition by 5Z-7-oxozeaenol is neuroprotective. The beneficial effect of 5Z-7-oxozeaenol was associated with a reduced activation of Jun kinase that leads to inflammation and apoptosis. Recently, other TAK1 inhibitors were developed suggesting that TAK1 may prove as an efficient therapeutic target for neurodegenerative diseases if safety issues are not limiting.

In search of the neuroprotective mechanism of thiazolidinediones in Parkinson's disease.

The oral antidiabetic thiazolidinediones exert protective effects in models of Parkinson's disease and other neurological diseases. While the antidiabetic effect is due to activation of PPARγ, the mechanisms underlying the neuroprotection are more controversial. It may involve activation of PPARγ blocking inflammation and apoptosis. However, new evidence suggests an antioxidative PPARγ-independent action. Here we discuss recent data on the mode of action of TZDs in models of PD and their implication for the translation into the clinic.

TAK1 in brain endothelial cells mediates fever and lethargy.

Systemic inflammation affects the brain, resulting in fever, anorexia, lethargy, and activation of the hypothalamus-pituitary-adrenal axis. How peripheral inflammatory signals reach the brain is still a matter of debate. One possibility is that, in response to inflammatory stimuli, brain endothelial cells in proximity to the thermoregulatory centers produce cyclooxygenase 2 (COX-2) and release prostaglandin E2, causing fever and sickness behavior. We show that expression of the MAP kinase kinase kinase TAK1 in brain endothelial cells is needed for interleukin 1ß (IL-1ß)-induced COX-2 production. Exploiting the selective expression of the thyroxine transporter Slco1c1 in brain endothelial cells, we generated a mouse line allowing inducible deletion of Tak1 specifically in brain endothelium. Mice lacking the Tak1 gene in brain endothelial cells showed a blunted fever response and reduced lethargy upon intravenous injection of the endogenous pyrogen IL-1ß. In conclusion, we demonstrate that TAK1 in brain endothelial cells induces COX-2, most likely by activating p38 MAPK and c-Jun, and is necessary for fever and sickness behavior.

Pannexins in ischemia-induced neurodegeneration.

Pannexin 1 (Px1, Panx1) and pannexin 2 (Px2, Panx2) form large-pore nonselective channels in the plasma membrane of cells and were suggested to play a role in the pathophysiology of cerebral ischemia. To directly test a potential contribution of pannexins in ischemia-related mechanisms, we performed experiments in Px1(-/-), Px2(-/-), and Px1(-/-)Px2(-/-) knockout mice. IL-1ß release, channel function in astrocytes, and cortical spreading depolarization were not altered in Px1(-/-)Px2(-/-) mice, indicating that, in contrast to previous concepts, these processes occur normally in the absence of pannexin channels. However, ischemia-induced dye release from cortical neurons was lower, indicating that channel function in Px1(-/-)Px2(-/-) neurons was impaired. Furthermore, Px1(-/-)Px2(-/-) mice had a better functional outcome and smaller infarcts than wild-type mice when subjected to ischemic stroke. In conclusion, our data demonstrate that Px1 and Px2 underlie channel function in neurons and contribute to ischemic brain damage.

Influenza virus infection aggravates stroke outcome.

BACKGROUND AND PURPOSE: Stroke is triggered by several risk factors, including influenza and other respiratory tract infections. However, it is unknown how and in which way influenza infection affects stroke outcome. METHODS: We infected mice intranasally with human influenza A (H1N1) virus and occluded the middle cerebral artery to induce ischemic strokes. Infarct volume and intracerebral hemorrhage were determined by histology. To evaluate the integrity of the blood-brain barrier and inflammation, we measured various cytokines in vivo and in vitro and performed immunohistochemistry of leukocyte markers, collagen IV, immunoglobulins, and matrix metalloproteinase-9. RESULTS: Influenza virus infection increased infarct size. Whereas changes in cardiovascular parameters did not explain this effect, we found evidence for an inflammatory mechanism. In influenza virus infection, the respiratory tract released cytokines into the blood, such as RANTES that induced macrophage inflammatory protein-2 and other inflammatory mediators in the ischemic brain. In infected mice, there was an increased number of neutrophils expressing the matrix metalloproteinase-9 in the ischemic brain. This was accompanied by severe disruption of the blood-brain barrier and an increased rate of intracerebral hemorrhages after tissue plasminogen activator treatment. To investigate the role of cytokines, we blocked cytokine release by using GTS-21, a selective agonist of the α7 nicotinic acetylcholine receptor. GTS-21 ameliorated ischemic brain damage and improved survival. CONCLUSIONS: Influenza virus infection triggers a cytokine cascade that aggravates ischemic brain damage and increases the risk of intracerebral hemorrhage after tissue plasminogen activator treatment. Blockade of cytokine production by α7 nicotinic acetylcholine receptor agonists is a novel therapeutic option to treat stroke in a proinflammatory context.

Regulation of GDF-15, a distant TGF-ß superfamily member, in a mouse model of cerebral ischemia.

GDF-15 is a novel distant member of the TGF-ß superfamily and is widely distributed in the brain and peripheral nervous system. We have previously reported that GDF-15 is a potent neurotrophic factor for lesioned dopaminergic neurons in the substantia nigra, and that GDF-15-deficient mice show progressive postnatal losses of motor and sensory neurons. We have now investigated the regulation of GDF-15 mRNA and immunoreactivity in the murine hippocampal formation and selected cortical areas following an ischemic lesion by occlusion of the middle cerebral artery (MCAO). MCAO prominently upregulates GDF-15 mRNA in the hippocampus and parietal cortex at 3 h and 24 h after lesion. GDF-15 immunoreactivity, which is hardly detectable in the unlesioned brain, is drastically upregulated in neurons identified by double-staining with NeuN. NeuN staining reveals that most, if not all, neurons in the granular layer of the dentate gyrus and pyramidal layers of the cornu ammonis become GDF-15-immunoreactive. Moderate induction of GDF-15 immunoreactivity has been observed in a small number of microglial cells identified by labeling with tomato lectin, whereas astroglial cells remain GDF-15-negative after MCAO. Comparative analysis of the size of the infarcted area after MCAO in GDF-15 wild-type and knockout mice has failed to reveal significant differences. Together, our data substantiate the notion that GDF-15 is prominently upregulated in the lesioned brain and might be involved in orchestrating post-lesional responses other than the trophic support of neurons.