kcna1a mutant zebrafish model episodic ataxia type 1 (EA1) with epilepsy and show response to first-line therapy carbamazepine

OBJECTIVE

KCNA1 mutations are associated with a rare neurological movement disorder known as episodic ataxia type 1 (EA1), and epilepsy is a common comorbidity. Current medications provide only partial relief for ataxia and/or seizures, making new drugs needed. Here, we characterized zebrafish kcna1a-/- as a model of EA1 with epilepsy and compared the efficacy of the first-line therapy carbamazepine in kcna1a-/- zebrafish to Kcna1-/- rodents.

METHODS

CRISPR/Cas9 mutagenesis was used to introduce a mutation in the sixth transmembrane segment of the zebrafish Kcna1 protein. Behavioral and electrophysiological assays were performed on kcna1a-/- larvae to assess ataxia- and epilepsy-related phenotypes. Real-time quantitative polymerase chain reaction (qPCR) was conducted to measure mRNA levels of brain hyperexcitability markers in kcna1a-/- larvae, followed by bioenergetics profiling to evaluate metabolic function. Drug efficacies were tested using behavioral and electrophysiological assessments, as well as seizure frequency in kcna1a-/- zebrafish and Kcna1-/- mice, respectively.

RESULTS

Zebrafish kcna1a-/- larvae showed uncoordinated movements and locomotor deficits, along with scoliosis and increased mortality. The mutants also exhibited impaired startle responses when exposed to light-dark flashes and acoustic stimulation as well as hyperexcitability as measured by extracellular field recordings and upregulated fosab transcripts. Neural vglut2a and gad1b transcript levels were disrupted in kcna1a-/- larvae, indicative of a neuronal excitatory/inhibitory imbalance, as well as a significant reduction in cellular respiration in kcna1a-/- , consistent with dysregulation of neurometabolism. Notably, carbamazepine suppressed the impaired startle response and brain hyperexcitability in kcna1a-/- zebrafish but had no effect on the seizure frequency in Kcna1-/- mice, suggesting that this EA1 zebrafish model might better translate to humans than rodents.

SIGNIFICANCE

We conclude that zebrafish kcna1a-/- show ataxia and epilepsy-related phenotypes and are responsive to carbamazepine treatment, consistent with EA1 patients. These findings suggest that kcna1-/- zebrafish are a useful model for drug screening as well as studying the underlying disease biology.

Impaired retinoic acid signaling in cerebral cavernous malformations

The capillary-venous pathology cerebral cavernous malformation (CCM) is caused by loss of CCM1/Krev interaction trapped protein 1 (KRIT1), CCM2/MGC4607, or CCM3/PDCD10 in some endothelial cells. Mutations of CCM genes within the brain vasculature can lead to recurrent cerebral hemorrhages. Pharmacological treatment options are urgently needed when lesions are located in deeply-seated and in-operable regions of the central nervous system. Previous pharmacological suppression screens in disease models of CCM led to the discovery that treatment with retinoic acid improved CCM phenotypes. This finding raised a need to investigate the involvement of retinoic acid in CCM and test whether it has a curative effect in preclinical mouse models. Here, we show that components of the retinoic acid synthesis and degradation pathway are transcriptionally misregulated across disease models of CCM. We complemented this analysis by pharmacologically modifying retinoic acid levels in zebrafish and human endothelial cell models of CCM, and in acute and chronic mouse models of CCM. Our pharmacological intervention studies in CCM2-depleted human umbilical vein endothelial cells (HUVECs) and krit1 mutant zebrafish showed positive effects when retinoic acid levels were increased. However, therapeutic approaches to prevent the development of vascular lesions in adult chronic murine models of CCM were drug regiment-sensitive, possibly due to adverse developmental effects of this hormone. A treatment with high doses of retinoic acid even worsened CCM lesions in an adult chronic murine model of CCM. This study provides evidence that retinoic acid signaling is impaired in the CCM pathophysiology and suggests that modification of retinoic acid levels can alleviate CCM phenotypes.

Myostatin is a negative regulator of adult neurogenesis after spinal cord injury in zebrafish

Intrinsic and extrinsic inhibition of neuronal regeneration obstruct spinal cord (SC) repair in mammals. In contrast, adult zebrafish achieve functional recovery after complete SC transection. While studies of innate SC regeneration have focused on axon regrowth as a primary repair mechanism, how local adult neurogenesis affects functional recovery is unknown. Here, we uncover dynamic expression of zebrafish myostatin b (mstnb) in a niche of dorsal SC progenitors after injury. mstnb mutants show impaired functional recovery, normal glial and axonal bridging across the lesion, and an increase in the profiles of newborn neurons. Molecularly, neuron differentiation genes are upregulated, while the neural stem cell maintenance gene fgf1b is downregulated in mstnb mutants. Finally, we show that human fibroblast growth factor 1 (FGF1) treatment rescues the molecular and cellular phenotypes of mstnb mutants. These studies uncover unanticipated neurogenic functions for mstnb and establish the importance of local adult neurogenesis for innate SC repair.

A conserved CCM complex promotes apoptosis non-autonomously by regulating zinc homeostasis

Apoptotic death of cells damaged by genotoxic stress requires regulatory input from surrounding tissues. The C. elegans scaffold protein KRI-1, ortholog of mammalian KRIT1/CCM1, permits DNA damage-induced apoptosis of cells in the germline by an unknown cell non-autonomous mechanism. We reveal that KRI-1 exists in a complex with CCM-2 in the intestine to negatively regulate the ERK-5/MAPK pathway. This allows the KLF-3 transcription factor to facilitate expression of the SLC39 zinc transporter gene zipt-2.3, which functions to sequester zinc in the intestine. Ablation of KRI-1 results in reduced zinc sequestration in the intestine, inhibition of IR-induced MPK-1/ERK1 activation, and apoptosis in the germline. Zinc localization is also perturbed in the vasculature of krit1-/- zebrafish, and SLC39 zinc transporters are mis-expressed in Cerebral Cavernous Malformations (CCM) patient tissues. This study provides new insights into the regulation of apoptosis by cross-tissue communication, and suggests a link between zinc localization and CCM disease.

In vivo analysis of cardiomyocyte proliferation during trabeculation

Cardiomyocyte proliferation is crucial for cardiac growth, patterning and regeneration; however, few studies have investigated the behavior of dividing cardiomyocytes in vivo Here, we use time-lapse imaging of beating hearts in combination with the FUCCI system to monitor the behavior of proliferating cardiomyocytes in developing zebrafish. Confirming in vitro observations, sarcomere disassembly, as well as changes in cell shape and volume, precede cardiomyocyte cytokinesis. Notably, cardiomyocytes in zebrafish embryos and young larvae mostly divide parallel to the myocardial wall in both the compact and trabecular layers, and cardiomyocyte proliferation is more frequent in the trabecular layer. While analyzing known regulators of cardiomyocyte proliferation, we observed that the Nrg/ErbB2 and TGFβ signaling pathways differentially affect compact and trabecular layer cardiomyocytes, indicating that distinct mechanisms drive proliferation in these two layers. In summary, our data indicate that, in zebrafish, cardiomyocyte proliferation is essential for trabecular growth, but not initiation, and set the stage to further investigate the cellular and molecular mechanisms driving cardiomyocyte proliferation in vivo.

Opposite effects of Activin type 2 receptor ligands on cardiomyocyte proliferation during development and repair

Zebrafish regenerate damaged myocardial tissue very effectively. Hence, insights into the molecular networks underlying zebrafish heart regeneration might help develop alternative strategies to restore human cardiac performance. While TGF-β signaling has been implicated in zebrafish cardiac regeneration, the role of its individual ligands remains unclear. Here, we report the opposing expression response during zebrafish heart regeneration of two genes, mstnb and inhbaa, which encode TGF-β family ligands. Using gain-of-function (GOF) and loss-of-function (LOF) approaches, we show that these ligands mediate inverse effects on cardiac regeneration and specifically on cardiomyocyte (CM) proliferation. Notably, we find that Inhbaa functions as a CM mitogen and that its overexpression leads to accelerated cardiac recovery and scar clearance after injury. In contrast, mstnb GOF and inhbaa LOF both lead to unresolved scarring after cardiac injury. We further show that Mstnb and Inhbaa inversely control Smad2 and Smad3 transcription factor activities through alternate Activin type 2 receptors.

Zebrafish can regenerate damaged myocardial tissue but it is unclear how this is regulated. Here, the authors show that two TGF-β family members, Mstnb and Inhbaa, have opposite effects in regeneration, with mstnb overexpression or inhbaa loss-of-function causing cardiac scarring after injury.

Id4 functions downstream of Bmp signaling to restrict TCF function in endocardial cells during atrioventricular valve development

The atrioventricular canal (AVC) connects the atrial and ventricular chambers of the heart and its formation is critical for the development of the cardiac valves, chamber septation and formation of the cardiac conduction system. Consequently, problems in AVC formation can lead to congenital defects ranging from cardiac arrhythmia to incomplete cardiac septation. While our knowledge about early heart tube formation is relatively comprehensive, much remains to be investigated about the genes that regulate AVC formation. Here we identify a new role for the basic helix-loop-helix factor Id4 in zebrafish AVC valve development and function. id4 is first expressed in the AVC endocardium and later becomes more highly expressed in the atrial chamber. TALEN induced inactivation of id4 causes retrograde blood flow at the AV canal under heat induced stress conditions, indicating defects in AV valve function. At the molecular level, we found that id4 inactivation causes misexpression of several genes important for AVC and AV valve formation including bmp4 and spp1. We further show that id4 appears to control the number of endocardial cells that contribute to the AV valves by regulating Wnt signaling in the developing AVC endocardium.

Curcumin: a potential therapeutic polyphenol, prevents noradrenaline-induced hypertrophy in rat cardiac myocytes

OBJECTIVES

This study was designed to evaluate the effect of curcumin on H9c2 cardiac cell line and primary rat cardiac myocytes, using purified noradrenaline as a hypertrophy-inducing agent.

METHODS

The concentration of curcumin at which cells were treated was determined by MTT (3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay. The effect of this safe dose in preventing noradrenaline-induced cardiac hypertrophy was assessed by biochemical analysis (estimating total protein content), molecular analysis (using RT-PCR to study the expression of fetal genes like ANF), immunological analysis (by determining the nuclear localization of GATA-4) and electrophoretic mobility shift assay (EMSA; to study DNA binding activity of GATA-4).

KEY FINDINGS

Curcumin at a concentration of 8 µm was found to suppress the increase in cell size, protein content and enhanced marker gene expression (ANF) caused by noradrenaline. Immunocytochemistry and Western blot analysis showed that curcumin suppressed the localization of transcription factor GATA-4 in the nucleus. It also showed a reduced DNA-binding activity in the presence of noradrenaline as confirmed by EMSA.

CONCLUSIONS

These findings suggest that curcumin reduces the hypertrophic marker gene expression by inhibiting nuclear localization and DNA binding activity of GATA-4. Thus it has a great anti-hypertrophic potential.

Congenital generalized cutis laxa in two sisters

Two sisters, aged 2 and 3 years, having generalized cutis laxa, presenting with progressive loose pendulous skin since birth are reported.

Hypopigmented mycosis fungoides treated successfully with puva

Hypopigmented lesions are rarely encountered in mycosis fungoides. We here report a 22-year old female patient who presented with a 5-year history of asymptomatic progressively increasing discrete and confluent hypopigmented macules and a 1-year history of a few itchy erythematous, scaly, indurated plaques. The histological features were consistent with a clinical diagnosis of mycosis fungoides. She was successfully treated with PUVA therapy.

Lepromatous leprosy presenting as a swelling in the neck

A 25-year-old electrician presented with gradually, asymptomatic swelling on left of the neck since 2 years. The swelling which was initially diagnosed as cervical lymphadenitis by the internist represented the enlarged left great auricular nerve. Cutaneous examination revealed an ill-defined, hypoaesthetic macule with minimal atrophy on the pinna of the left ear. The histopathology of the nerve showed a lepromatous neuritis with bacteriological index (BI) of 5+.

Olmsted syndrome with hypotrichosis

Olmsted syndrome is characterised by mutilating palmoplantar keratoderma with peri-orificial hyperkeratosis. We report the case of an 8-year old boy who presented with severe keratoderma of the soles since birth and of the palms from the age of 3 years. At 3 years of age hyperkeratotic plaques appeared on the elbows and knees. The child developed keratotic lesions at the angle of the mouth 1 year later. The child had sparse thin easily pluckable hair. Light and scanning electron microscopic examination of the hair revealed several hair shaft abnormalities. Though the psychomotor development of the child was normal till 1 year of age, thereafter the keratoderma had largely restricted the child's mobility. There was no history of hyperhidrosis and no dental abnormality was detected. The lesions had been unresponsive to keratolytics and had recurred after surgical removal. The patient was started on oral retinoids and topical keratolytics and had partially responded in 2 months.

Cutaneous focal mucinosis

A 26-year-old male presented with asymptomatic, flesh coloured nodules on right elbow, forehead and right retroauricular region. A skin biopsy form the nodule stained with hematoxylin and eosin and special stain (mucicarmine) showed focal deposition of mucin in the dermis.

Subungual malignant melanoma clinically resembling granuloma pyogenicum

A 37-year-old labourer developed longitudinally split dystrophic nail with blackish discolouration in the centre 5 months following blunt trauma to the right thumb nail. Six months later, a well defined exudative erythematous to violaceous nodule developed and this recurred inspite of repeated surgical interventions. Patient had large, firm to hard epitrochlear and axillary lymphadenopathy. Histopathological examination confirmed the diagnosis of malignant melanoma.