Defective Signal Transduction Research Articles

Endothelial Cell GATA2 Modulates the Cardiomyocyte Stress Response through the Regulation of Two Long Non-Coding RNAs.

Capillary endothelial cells modulate myocardial growth and function during pathological stress, but it is unknown how and whether this contributes to the development of heart failure. We found that the endothelial cell transcription factor GATA2 is downregulated in human failing myocardium. Endothelial GATA2 knock-out (G2-EC-KO) mice develop heart failure and defective myocardial signal transduction during pressure overload, indicating that the GATA2 downregulation is maladaptive. Heart failure and perturbed signaling in G2-EC-KO mice could be induced by strong upregulation of two unknown, endothelial cell-derived long non-coding (lnc) RNAs (AK037972, AK038629, termed here GADLOR1 and 2). Mechanistically, the GADLOR1/2 lncRNAs transfer from endothelial cells to cardiomyocytes, where they block stress-induced signalling. Thereby, lncRNAs can contribute to disease as paracrine effectors of signal transduction and therefore might serve as therapeutic targets in the future.

Cilia-localized GID/CTLH ubiquitin ligase complex regulates protein homeostasis of sonic hedgehog signaling components.

ABSTRACTCilia are evolutionarily conserved organelles that orchestrate a variety of signal transduction pathways, such as sonic hedgehog (SHH) signaling, during embryonic development. Our recent studies have shown that loss of GID ubiquitin ligase function results in aberrant AMP-activated protein kinase (AMPK) activation and elongated primary cilia, which suggests a functional connection to cilia. Here, we reveal that the GID complex is an integral part of the cilium required for primary cilia-dependent signal transduction and the maintenance of ciliary protein homeostasis. We show that GID complex subunits localize to cilia in both Xenopus laevis and NIH3T3 cells. Furthermore, we report SHH signaling pathway defects that are independent of AMPK and mechanistic target of rapamycin (MTOR) activation. Despite correct localization of SHH signaling components at the primary cilium and functional GLI3 processing, we find a prominent reduction of some SHH signaling components in the cilium and a significant decrease in SHH target gene expression. Since our data reveal a critical function of the GID complex at the primary cilium, and because suppression of GID function in X. laevis results in ciliopathy-like phenotypes, we suggest that GID subunits are candidate genes for human ciliopathies that coincide with defects in SHH signal transduction.

The altered osteocytic expression of connexin 43 and sclerostin in human cadaveric donors with alcoholic liver cirrhosis: Potential treatment targets.

Previous studies suggested that osteocyte lacunar network disruption could play a role in the complex pathophysiology of bone changes in aging and disease. Considering that particular research interest is lacking, we aimed to assess alcoholic liver cirrhosis (ALC)-induced changes in osteocyte lacunar network and bone marrow adiposity. Immunohistochemistry was conducted to assess changes in the micro-morphology of osteocyte lacunar network and bone marrow adiposity, and expression of connexin 43 and sclerostin in vertebral and femoral samples collected from 40 cadaveric men (age range between 44 and 70years) divided into ALC group (n=20) and control group (n=20). Furthermore, the assessment of the potential association between bone changes and the severity of the hepatic disorder (given by Knodell's pathohistologic scoring) was conducted. Our data revealed fewer connexin 43-positive osteocytes per vertebral and femoral bone area (p<0.01), suggesting defective signal transduction among osteocytes in ALC individuals. Moreover, we found an ALC-induced increase in the number of adipocytes in the vertebral bone marrow (p=0.038). Considering significant associations between the severity of liver tissue disturbances and impaired functionality of osteocyte lacunar network (Pearson's correlation analyses, p<0.05), we may assume that timely treatment of the liver disease may delay bone impairment. ALC induced an increase in osteocytic sclerostin expression (p<0.001), suggesting its role in mediating low bone formation among ALC individuals. Hence, medicaments targeting low bone formation may be beneficial to attenuate the bone changes among ALC patients. However, future clinical studies are required to verify the therapeutic utility of these findings.

Mechanisms for the development of heart failure and improvement of cardiac function by angiotensin-converting enzyme inhibitors

Angiotensin-converting enzyme (ACE) inhibitors, which prevent the conversion of angiotensin I to angiotensin II, are well-known for the treatments of cardiovascular diseases, such as heart failure, hypertension and acute coronary syndrome. Several of these inhibitors including captopril, enalapril, ramipril, zofenopril and imidapril attenuate vasoconstriction, cardiac hypertrophy and adverse cardiac remodeling, improve clinical outcomes in patients with cardiac dysfunction and decrease mortality. Extensive experimental and clinical research over the past 35 years has revealed that the beneficial effects of ACE inhibitors in heart failure are associated with full or partial prevention of adverse cardiac remodeling. Since cardiac function is mainly determined by coordinated activities of different subcellular organelles, including sarcolemma, sarcoplasmic reticulum, mitochondria and myofibrils, for regulating the intracellular concentration of Ca2+ and myocardial metabolism, there is ample evidence to suggest that adverse cardiac remodelling and cardiac dysfunction in the failing heart are the consequence of subcellular defects. In fact, the improvement of cardiac function by different ACE inhibitors has been demonstrated to be related to the attenuation of abnormalities in subcellular organelles for Ca2+-handling, metabolic alterations, signal transduction defects and gene expression changes in failing cardiomyocytes. Various ACE inhibitors have also been shown to delay the progression of heart failure by reducing the formation of angiotensin II, the development of oxidative stress, the level of inflammatory cytokines and the occurrence of subcellular defects. These observations support the view that ACE inhibitors improve cardiac function in the failing heart by multiple mechanisms including the reduction of oxidative stress, myocardial inflammation and Ca2+-handling abnormalities in cardiomyocytes.

Defective Signal Transduction in Osteoarthritic Chondrocytes and Synovial Fibroblasts Should Become a Target for Drug Intervention

Although it has been known for some time that pro-inflammatory cytokines are an essential driver of synovial joint inflammation in osteoarthritis (OA), drugs [e.g. Anakinra, Tocilizumab, Tofacitinib, Adalibumab] that target the signal transduction pathways activated by these cytokines

Hemorrhagic thrombocytopathy with defective signal transduction CalDAG-GEFI

Hemorrhagic thrombocytopathy with defective signal transduction CalDAG-GEFI is a rare disease associated with a mutation in the RASGRP2 gene. At the moment, this disease is described in 10 person in the world. We present clinical case report of this pathology of a 9-year-old child. We also offer a review of the available literature about pathogenetic features, clinical manifestations and prevalence of this rare disease. The patient’s parents gave their consent to the use of their child’s data, including photographs, for research purposes and in publications.

Evaluation of serum pancreatic enzymes in type 2 diabetes mellitus and its correlation with insulin resistance

Introduction: Type 2 diabetes mellitus is due to the decreased biological response to insulin or insulin resistance. Insulin resistance develops as a consequence of defects in signal transduction by insulin. These defects may also affect the exocrine pancreatic function. The aim of this study was to determine serum pancreatic enzyme levels in diabetic patients and to correlate them with insulin resistance. Materials and Methods: In this case control study we compared fasting blood sugar, serum insulin, lipase and amylase levels and insulin resistance in diabetic and normal healthy adults. The correlation of pancreatic enzymes with insulin resistance was also studied. Results: Diabetic group showed statistically significant increase in all the parameters compared to control group. Serum amylase showed a significant negative correlation with insulin resistance (p=0.007) and serum lipase a positive correlation with insulin resistance, but it was not significant (p =0.119). Conclusion: The study showed a significant alteration in the exocrine pancreatic function in diabetic patients. There is a negative correlation between serum amylase level and insulin resistance. Keywords: Amylase, Insulin Resistance, Islet-Acinar Axis, Lipase, Type 2 Diabetes Mellitus.

Primary familial brain calcification presenting as paroxysmal kinesigenic dyskinesia: Genetic and functional analyses

BackgroundPrimary familial brain calcification (PFBC) is a rare neurodegenerative disorder characterized by calcium deposition in bilateral and symmetric brain. Evidence suggested that PFBC might be associated with paroxysmal kinesigenic dyskinesia (PKD). We aim to investigate the genetic causes in PFBC patients manifested as PKD, and further to explore the pathogenic impact of the identified mutations. Methods4 PKD-mimic PFBC patients were investigated in the study. Clinical assessment including laboratory tests, head computed tomography (CT) were conducted and followed by exome sequencing. Variants of PFBC genes were screened, and Sanger sequencing, segregation analysis were applied to confirm the findings. Functional assessment of the identified mutations was further analyzed. ResultsAmong the 4 PKD-mimic PFBC patients, 3 presented with brain calcification, and 1 was identified carrying a PFBC mutation but without brain calcification. The clinical characteristics were summarized. Three heterozygous variants (2 novel, 1 documented) in PFBC genes were found. Further functional study showed abnormal accumulation and reduced uptake of Pi of the mutant protein, and the aggregated PDGFB failing to induce membrane ruffles compared with wild-type. ConclusionsPKD can be a manifestation of PFBC, and brain calcification may be a cause of secondary PKD. So thoroughly evaluation including head CT or genetic screening for paroxysmal dyskinesia and PFBC should be applied before the diagnosis of PKD or PFBC. Moreover, negative brain calcification may not exclude the possibility of PFBC. The possible pathogenesis of primary calcification lie in the dysfunction of the protein or defective signal transduction caused by the mutations.

Claudin7-dependent exosome-promoted reprogramming of nonmetastasizing tumor cells.

Claudin7 (cld7) is a cancer-initiating cell (CIC) marker in gastrointestinal tumors, a cld7-knockdown (kd) being accompanied by loss of tumor progression. Tumor exosomes (TEX) restoring CIC activities, we explored the contribution of cld7. This became particularly interesting, as tight junction (TJ)- and glycolipid-enriched membrane domain (GEM)-derived cld7 is recruited into distinct TEX. TEXs were derived from CIC or cld7kd cells of a rat pancreatic and a human colon cancer line. TEX derived from pancreatic cancer cld7kd cells rescued with palmitoylation site-deficient cld7 (cld7mP) allowed selectively evaluating the contribution of GEM-derived TEX, only palmitoylated cld7 being integrated into GEM. Cld7 CIC-TEX promoted tumor cell dissemination and metastatic growth without a major impact on proliferation, apoptosis resistance and epithelial-mesenchymal transition. Instead, migration, invasion and (lymph)angiogenesis were strongly supported, only migration being selectively fostered by GEM-derived cld7 TEX. CIC-TEX coculture of cld7kd cells uncovered significant changes in the cld7kd cell protein and miRNA profiles. However, changes did not correspond to the CIC-TEX profile, CIC-TEX rather initiating integrin, protease and RTK, particularly lymphangiogenic receptor activation. CIC-TEX preferentially rescuing cld7kd-associated defects in signal transduction was backed up by an RTK inhibitor neutralizing the impact of CIC-TEX on tumor progression. In conclusion, cld7 contributes to selective steps of the metastatic cascade. Defects of cld7kd and cld7mP cells in migration, invasion and (lymph)angiogenesis are effaced by CIC-TEX that act by signaling cascade activation. Accordingly, RTK inhibitors are an efficient therapeutic defeating CIC-TEX.

Androgens and Severe Insulin Resistance States: Basic and Clinical Aspects.

Hyperandrogenism with or without polycystic ovary syndrome can be sustained by an extreme form of insulin resistance (IR), and is thus a secondary form of hyperandrogenism, which may be due to a defect in insulin signal transduction or in the adipose tissue. Severe IR due to adipose tissue dysfunction is the most frequent form, which may be the result of a deficiency in the adipose tissue, that is, the lipodystrophies, or to the unrestrained accumulation of adipose tissue. These forms are in some cases produced by a single-gene defect. The diagnosis remains predominantly clinical by examining patients in their underwear and looking out for clinical hallmarks, supported by biochemical biomarkers. Gene screening is necessary to corroborate the diagnosis of some forms. Clinicians who deal with hyperandrogenic disorders should be alerted to the forms that are secondary to severe IR, as they are not as uncommon as often imagined and frequently respond to tailored therapies.

Dynamics of cell signaling and decoding

Signal Transduction Defects in cellular signaling pathways, like those in some cancer cells, are often thought to result in increased or decreased steady-state signals that promote or inhibit cell proliferation. But Bugaj et al. show that dynamic changes in the duration or frequency of a signal can also alter cellular responses (see the Perspective by Kolch and Kiel). They took precise control of signaling in cultured human or mouse cells with a light-controlled mechanism for activating and inactivating the guanosine triphosphate Ras. Known cancer mutations in components of the Ras-activated signaling pathway or inhibitors of particular pathway components altered signal timing and readouts. The modified dynamics changed transcriptional outcomes and could inappropriately support cell proliferation. The ability to probe responses of signaling networks in this way may enhance understanding of biological regulation and reveal new therapeutic targets. Science , this issue p. [eaao3048][1]; see also p. [844][2] [1]: /lookup/doi/10.1126/science.aao3048 [2]: /lookup/doi/10.1126/science.aau8059

Epidermal expression of a sterol biosynthesis gene regulates root growth by a non-cell-autonomous mechanism in Arabidopsis.

ABSTRACTThe epidermis is hypothesized to play a signalling role during plant development. One class of mutants showing defects in signal transduction and radial patterning are those in sterol biosynthesis. The expectation is that living cells require sterols, but it is not clear that all cell types express sterol biosynthesis genes. The HYDRA1 (HYD1) gene of Arabidopsis encodes sterol Δ8-Δ7 isomerase, and although hyd1 seedlings are defective in radial patterning across several tissues, we show that the HYD1 gene is expressed most strongly in the root epidermis. Transgenic activation of HYD1 transcription in the epidermis of hyd1 null mutants reveals a major role in root patterning and growth. HYD1 expression in the vascular tissues and root meristem, though not endodermis or pericycle, also leads to some phenotypic rescue. Phenotypic rescue is associated with rescued patterning of the PIN1 and PIN2 auxin efflux carriers. The importance of the epidermis in controlling root growth and development is proposed to be, in part, due to its role as a site for sterol biosynthesis, and auxin is a candidate for the non-cell-autonomous signal.

Effect of Hyperglycemia on Purinergic and Nitrergic Inhibitory Neuromuscular Transmission in the Antrum of the Stomach: Implications for Fast Gastric Emptying.

Hyperglycemia has been reported to enhance vagovagal reflex that causes the release of inhibitory neurotransmitter, nitric oxide (NO), at the neuromuscular junction in the antrum to relax the antrum and slow gastric emptying by stimulating glucose-sensitive afferent neurons. However, hyperglycemia has also been reported to cause fast gastric emptying that may be due to suppression of the inhibitory motor neurons. The purpose of the present study was to investigate changes in inhibitory neuromuscular transmission in the gastric antrum due to hyperglycemia. Inhibitory electrical junction potentials were recorded from gastric antral muscle strips, using intracellular electrodes under non-adrenergic, non-cholinergic conditions. Studies were performed in non-hyperglycemic NOD (NH-NOD), NOD mice as they develop hyperglycemia (H-NOD) and their age-matched controls. The purinergic inhibitory junction potential (pIJP) and nitrergic IJP (nIJP) were isolated pharmacologically. The control pIJP was large, around -18 mV and nIJP was small, around -9 mV. In NH-NOD the IJPs were not affected, but in H-NOD pIJP was nearly abolished and nIJP was significantly reduced. In H-NOD mice, membrane hyperpolarization caused by exogenous α,β-MeATP or diethylenetriamine NO adduct was similar to that in wild-type controls (P > 0.05). H-NOD smooth muscles were significantly depolarized as compared to NH-NOD smooth muscles. These observations show that hyperglycemia causes suppression of purinergic and nitrergic transmission by acting on the motor neurons that form the last neuron in the vagovagal circuit. Moreover, the loss the neurotransmission is due to a defect in neurotransmitter release rather than a defect in signal transduction. Hyperglycemia also causes depolarization of smooth muscles that may increase their excitability.

Type 1 diabetes alters lipid handling and metabolism in human fibroblasts and peripheral blood mononuclear cells.

Triggers of the autoimmune response that leads to type 1 diabetes (T1D) remain poorly understood. A possibility is that parallel changes in both T cells and target cells provoke autoimmune attack. We previously documented greater Ca2+ transients in fibroblasts from T1D subjects than non-T1D after exposure to fatty acids (FA) and tumor necrosis factor α (TNFα). These data indicate that metabolic and signal transduction defects present in T1D can be elicited ex vivo in isolated cells. Changes that precede T1D, including inflammation, may activate atypical responses in people that are genetically predisposed to T1D. To identify such cellular differences in T1D, we quantified a panel of metabolic responses in fibroblasts and peripheral blood cells (PBMCs) from age-matched T1D and non-T1D subjects, as models for non-immune and immune cells, respectively. Fibroblasts from T1D subjects accumulated more lipid, had higher LC-CoA levels and converted more FA to CO2, with less mitochondrial proton leak in response to oleate alone or with TNFα, using the latter as a model of inflammation. T1D-PBMCs contained and also accumulated more lipid following FA exposure. In addition, they formed more peroxidized lipid than controls following FA exposure. We conclude that both immune and non-immune cells in T1D subjects differ from controls in terms of responses to FA and TNFα. Our results suggest a differential sensitivity to inflammatory insults and FA that may precede and contribute to T1D by priming both immune cells and their targets for autoimmune reactions.

Ciliopathy Protein Tmem107 Plays Multiple Roles in Craniofacial Development

A broad spectrum of human diseases called ciliopathies is caused by defective primary cilia morphology or signal transduction. The primary cilium is a solitary organelle that responds to mechanical and chemical stimuli from extracellular and intracellular environments. Transmembrane protein 107 (TMEM107) is localized in the primary cilium and is enriched at the transition zone where it acts to regulate protein content of the cilium. Mutations in TMEM107 were previously connected with oral-facial-digital syndrome, Meckel-Gruber syndrome, and Joubert syndrome exhibiting a range of ciliopathic defects. Here, we analyze a role of Tmem107 in craniofacial development with special focus on palate formation, using mouse embryos with a complete knockout of Tmem107. Tmem107–/– mice were affected by a broad spectrum of craniofacial defects, including shorter snout, expansion of the facial midline, cleft lip, extensive exencephaly, and microphthalmia or anophthalmia. External abnormalities were accompanied by defects in skeletal structures, including ossification delay in several membranous bones and enlargement of the nasal septum or defects in vomeronasal cartilage. Alteration in palatal shelves growth resulted in clefting of the secondary palate. Palatal defects were caused by increased mesenchymal proliferation leading to early overgrowth of palatal shelves followed by defects in their horizontalization. Moreover, the expression of epithelial stemness marker SOX2 was altered in the palatal shelves of Tmem107–/– animals, and differences in mesenchymal SOX9 expression demonstrated the enhancement of neural crest migration. Detailed analysis of primary cilia revealed region-specific changes in ciliary morphology accompanied by alteration of acetylated tubulin and IFT88 expression. Moreover, Shh and Gli1 expression was increased in Tmem107–/– animals as shown by in situ hybridization. Thus, TMEM107 is essential for proper head development, and defective TMEM107 function leads to ciliary morphology disruptions in a region-specific manner, which may explain the complex mutant phenotype.

Metabolic disorders in polycystic ovary syndrome.

Polycystic ovary syndrome (PCOS) is a complex disease. Depending on the used criteria the prevalence of PCOS ranges from 6 to 20%. It is necessary to exclude diseases leading to androgen excess. The participation of genetic and environmental factors is considered in the etiology of PCOS development. The highest rate of incidence of PCOS is assessed in girls who were born SGA and developed premature adrenarche later in life.The free androgen index (FAI) is concerned as the most sensitive marker of hyperandrogenaemia in PCOS although insulin resistance, anti-Müllerian hormone (AMH),and deficiency of vitamin D may intensify metabolic disturbances. The ultrasound criteria used in adolescent patients prefer the estimation of the ovarian volume or the ratio of ovarian stroma to total ovary, rather than the number of ovarian follicles. PCOS is connected with different metabolic disorders. Post-binding defect in signal transduction is responsible for insulin resistance. This defect results from an impaired activity of the kinase receptor. Moreover, the adipose tissue of PCOS women differs substantially from the tissue of the others according to morphology and function. The adipocytes produce lower amounts of adiponectin, which is an insulin-sensitizing agent. Dyspidemia with high triglycerides and low high density lipoprotein cholesterol concentrations is frequently noticed. Cardio-metabolic risk factors, insulin resistance, and endothelial dysfunction accompany PCOS from the very beginning. Oxidative stress plays a role as a link among systemic inflammation and dysfunction of endothelial cells and abnormal thecal cell action. The treatment efforts in PCOS depend on the patient's main problems. Modification of diet and lifestyle is the most important recommended advice to each woman independent of age and weight.

Susceptibility genes for nontuberculous mycobacterial disease.

The number of patients with nontuberculous mycobacterial (NTM) disease is reportedly increasing both in Japan and worldwide. NTM diseases are classified into disseminated and pulmonary diseases based on their clinical characteristics. These two types of NTM diseases are thought to be controlled by different mechanisms. Disseminated NTM disease is caused by a defect in signal transduction of Th1 cellular immune responses, including the IFN-γ/IL-12 axis. The precise molecular mechanisms of disseminated NTM disease are understood in detail. Pulmonary NTM disease progression is associated with both bacterial factors as well as host factors. Furthermore, it is suggested that some susceptibility genes for NTM diseases may also exist. A previous study on the susceptibility genes for pulmonary NTM disease was performed using Single Nucleotide Polymorphism (SNP) analysis and microsatellite marker analysis. However, a number of challenges remain in terms of the reproducibility. The emergence of next generation sequencing enables genome-wide analysis, and further studies on the susceptibility genes for pulmonary NTM disease are expected in the future.

Defective Platelet Activation and Bleeding Complications upon Cholestasis in Mice

Background/Aims: Platelets are essential mediators of hemostasis to avoid excessive blood loss. Cirrhosis and chronic liver diseases are characterized by alterations in hemostasis. Alterations in the secondary hemostasis have been well studied, while defects in primary hemostasis, especially the consequences of cholestatic liver disease on platelet function are not well defined. Methods: After bile duct ligation (BDL) platelet activation and thrombus formation were analyzed in mice. Results: BDL in mice had a moderate effect on platelet counts; however, intrinsic platelet activation was strongly reduced upon activation of the collagen receptor GPVI at early time points. 7 days after bile duct ligation, platelets displayed an almost complete loss of activation with reduced agonist-triggered release of alpha and dense granules and expression of integrin α_IIbβ₃ on the platelet surface. This activation defects resulted in strongly reduced thrombus formation under flow, reduced platelet adhesion to fibrinogen and bleeding complications in BDL mice as measured by tail bleeding experiments. Mechanistically, elevated nitric oxide and prostacyclin levels induced phosphorylation of Vasodilator-stimulated phosphoprotein (VASP), an established inhibitor of platelet activation. Furthermore increased tissue plasminogen activator in plasma of BDL mice led to enhanced plasmin levels that might be responsible for reduced glycoprotein expression of BDL platelets. Besides, high amounts of bile acids contribute to defective signal transduction as shown in platelets from mice fed with a cholic acid diet. Conclusions: Cholestatic liver disease induces multiple platelet activation defects and impairs thrombus formation responsible for bleeding complications at least in mice.

Skeletal Muscle TRIB3 Mediates Glucose Toxicity in Diabetes and High- Fat Diet-Induced Insulin Resistance.

In the current study, we used muscle-specific TRIB3 overexpressing (MOE) and knockout (MKO) mice to determine whether TRIB3 mediates glucose-induced insulin resistance in diabetes and whether alterations in TRIB3 expression as a function of nutrient availability have a regulatory role in metabolism. In streptozotocin diabetic mice, TRIB3 MOE exacerbated, whereas MKO prevented, glucose-induced insulin resistance and impaired glucose oxidation and defects in insulin signal transduction compared with wild-type (WT) mice, indicating that glucose-induced insulin resistance was dependent on TRIB3. In response to a high-fat diet, TRIB3 MOE mice exhibited greater weight gain and worse insulin resistance in vivo compared with WT mice, coupled with decreased AKT phosphorylation, increased inflammation and oxidative stress, and upregulation of lipid metabolic genes coupled with downregulation of glucose metabolic genes in skeletal muscle. These effects were prevented in the TRIB3 MKO mice relative to WT mice. In conclusion, TRIB3 has a pathophysiological role in diabetes and a physiological role in metabolism. Glucose-induced insulin resistance and insulin resistance due to diet-induced obesity both depend on muscle TRIB3. Under physiological conditions, muscle TRIB3 also influences energy expenditure and substrate metabolism, indicating that the decrease and increase in muscle TRIB3 under fasting and nutrient excess, respectively, are critical for metabolic homeostasis.

Impaired TrkB Signaling Underlies Reduced BDNF-Mediated Trophic Support of Striatal Neurons in the R6/2 Mouse Model of Huntington's Disease.

The principal projection neurons of the striatum are critically dependent on an afferent supply of brain derived neurotrophic factor (BDNF) for neurotrophic support. These neurons express TrkB, the cognate receptor for BDNF, which activates signaling pathways associated with neuronal survival and phenotypic maintenance. Impairment of the BDNF-TrkB pathway is suspected to underlie the early dysfunction and prominent degeneration of striatal neurons in Huntington disease (HD). Some studies in HD models indicate that BDNF supply is reduced, while others suggest that TrkB signaling is impaired earlier in disease progression. It remains important to determine whether a primary defect in TrkB signaling underlies reduced neurotrophic support and the early vulnerability of striatal neurons in HD. Using the transgenic R6/2 mouse model of HD we found that prior to striatal degeneration there are early deficits in striatal protein levels of activated phospho-TrkB and the downstream-regulated protein DARPP-32. In contrast, total-TrkB and BDNF protein levels remained normal. Primary neurons cultured from R6/2 striatum exhibited reduced survival in response to exogenous BDNF applications. Moreover, BDNF activation of phospho-TrkB and downstream signal transduction was attenuated in R6/2 striatal cultures. These results suggest that neurotrophic support of striatal neurons is attenuated early in disease progression due to defects in TrkB signal transduction in the R6/2 model of HD.