Conserved transcriptional activity and ligand responsiveness of avian PPARs: Potential role in regulating lipid metabolism in mirgratory birds.

Migratory birds undergo metabolic remodeling in tissues, including increased lipid storage in white adipose and fatty acid uptake and oxidation in skeletal muscle, to optimize energy substrate availability and utilization in preparation for long-distance flight. Different tissues undergo gene expression changes in keeping with their specialized functions and driven by tissue specific transcriptional pathways. Peroxisome proliferator-activated receptors (PPARs) are lipid-activated nuclear receptors that regulate metabolic pathways involved in lipid and glucose utilization or storage in mammals. To examine whether PPARs might mediate fatty acid activation of metabolic gene programs that would be relevant during pre-migratory fattening, we used gray catbird as the focal species. PPAR isoforms cloned from catbird share high amino acid identity with mammalian homologs (% vs human): gcPPARα (88.1%), gcPPARδ (87.3%), gcPPARγ (91.2%). We tested whether gcPPARs activated fatty acid (FA) utilization genes using Lpl and Cpt1b gene promoter-luciferase reporters in mammalian cell lines. In C2C12 mouse myocytes gcPPARα was broadly activated by the saturated and unsaturated FAs tested; while gcPPARδ showed highest activation by the mono-unsaturated FA, 18:1 oleic acid (+80%). In CV-1 monkey kidney cells gcPPARγ responded to the poly-unsaturated fatty acid, 20:5 eicosapentaenoic acid (+60%). Moreover, in agreement with their structural conservation, gcPPARs were activated by isoform selective synthetic agonists similar to the respective mammalian isoform. Adenoviral mediated over-expression of PPARα in C2C12 myocytes induced expression of genes involved in fatty acid transport, including Cd36/Fat, as well as Cpt1b, which mediates a key rate limiting step of mitochondrial ß-oxidation. These gene expression changes correlated with increased lipid droplet accumulation in C2C12 myoblasts and differentiated myotubes and enhanced ß-oxidation in myotubes. Collectively, the data predict that the PPARs play a conserved role in gray catbirds to regulate lipid metabolism in target tissues that undergo metabolic remodeling throughout the annual migratory cycle.

Intermediate filament dysregulation in astrocytes in the human disease model of KLHL16 mutation in giant axonal neuropathy (GAN).

Giant Axonal Neuropathy (GAN) is a pediatric neurodegenerative disease caused by KLHL16 mutations. KLHL16 encodes gigaxonin, which regulates intermediate filament (IF) turnover. Previous neuropathological studies and examination of postmortem brain tissue in the current study revealed involvement of astrocytes in GAN. To develop a clinically-relevant model, we reprogrammed skin fibroblasts from seven GAN patients to pluripotent stem cells (iPSCs), which were used to generate neural progenitor cells (NPCs), astrocytes, and brain organoids. Multiple isogenic control clones were derived via CRISPR/Cas9 gene editing of one patient line carrying the G332R gigaxonin mutation. All GAN iPSCs were deficient for gigaxonin and displayed patient-specific increased vimentin expression. GAN NPCs had lower nestin expression and fewer nestin-positive cells compared to isogenic controls, but nestin morphology was unaffected. GAN brain organoids were marked by the presence of neurofilament and GFAP aggregates. GAN iPSC-astrocytes displayed striking dense perinuclear vimentin and GFAP accumulations and abnormal nuclear morphology. In over-expression systems, GFAP oligomerization and perinuclear aggregation were augmented in the presence of vimentin. GAN patient cells with large perinuclear vimentin aggregates accumulated significantly more nuclear KLHL16 mRNA compared to cells without vimentin aggregates. As an early effector of KLHL16 mutations, vimentin may be a potential target in GAN.

Intermediate filament dysregulation and astrocytopathy in the human disease model of KLHL16 mutation in giant axonal neuropathy (GAN).

Giant Axonal Neuropathy (GAN) is a pediatric neurodegenerative disease caused by KLHL16 mutations. KLHL16 encodes gigaxonin, a regulator of intermediate filament (IF) protein turnover. Previous neuropathological studies and our own examination of postmortem GAN brain tissue in the current study revealed astrocyte involvement in GAN. To study the underlying mechanisms, we reprogrammed skin fibroblasts from seven GAN patients carrying different KLHL16 mutations to iPSCs. Isogenic controls with restored IF phenotypes were derived via CRISPR/Cas9 editing of one patient carrying a homozygous missense mutation (G332R). Neural progenitor cells (NPCs), astrocytes, and brain organoids were generated through directed differentiation. All GAN iPSC lines were deficient for gigaxonin, which was restored in the isogenic control. GAN iPSCs displayed patient-specific increased vimentin expression, while GAN NPCs had decreased nestin expression compared to isogenic control. The most striking phenotypes were observed in GAN iPSC-astrocytes and brain organoids, which exhibited dense perinuclear IF accumulations and abnormal nuclear morphology. GAN patient cells with large perinuclear vimentin aggregates accumulated nuclear KLHL16 mRNA. In over-expression studies, GFAP oligomerization and perinuclear aggregation were potentiated in the presence of vimentin. As an early effector of KLHL16 mutations, vimentin may serve as a potential therapeutic target in GAN.

Chronic kidney disease emerging trends in children and what to do about it.

Chronic Kidney disease (CKD) is a major public health problem associated with increased health costs, morbidity, and mortality. There is a 30-fold higher mortality rate and severely impaired quality of life in children with chronic kidney disease (CKD), requiring dialysis or kidney transplant compared to the aged-match general population. The early diagnosis and treatment of pediatric CKD can reverse, delay or prevent progression to advanced kidney disease. It is worth noting that CKD with rapid progression, which carries a poor prognosis, is more common in African American children. Thus, the development of a universal pediatric CKD screening program for high-risk children can be vital for social equity. The disparity in prevalence and severity of CKD is likely due to a complex interaction between biological and nonbiological risk factors that influence the development and progression of CKD in children of African descent. For example, high-risk alleles in the gene encoding for apolipoprotein L1 (APOL1) have been recognized as the most important factor in the high incidence of some chronic kidney diseases in African Americans. In this review, we will focus on the trends in the incidence of pediatric CKD and management strategies aimed at enhancing health outcomes and reducing disease progression.

Effects of the serotonin 5-HT1B receptor agonist CP 94253 on the locomotor activity and body temperature of preweanling and adult male and female rats.

Serotonin 5-HT1A receptor agonists increase locomotor activity of both preweanling and adult rodents. The part played by the 5-HT1B receptor in locomotion is less certain, with preliminary evidence suggesting that the actions of 5-HT1B receptor agonists are not uniform across ontogeny. To more fully examine the role of 5-HT1B receptors, locomotor activity and axillary temperatures of preweanling and adult male and female rats was assessed. In the first experiment, adult (PD 70) and preweanling (PD 10 and PD 15) male and female rats were injected with the 5-HT1B agonist CP 94253 (2.5-10 mg/kg) immediately before locomotor activity testing and 60 min before axillary temperatures were recorded. In the second experiment, specificity of drug action was determined in PD 10 rats by administering saline, WAY 100635 (a 5-HT1A antagonist), or GR 127935 (a 5-HT1B antagonist) 30 min before CP 94253 (10 mg/kg) treatment. CP 94253 significantly increased the locomotor activity of preweanling rats on PD 10, an effect that was fully attenuated by GR 127935. Conversely, CP 94253 significantly decreased the locomotor activity of male and female adult rats, while CP 94253 did not affect the locomotor activity of PD 15 rats. Regardless of age, CP 94253 (2.5-10 mg/kg) significantly reduced the axillary temperatures of preweanling and adult rats. When considered together, these results show that 5-HT1B receptor stimulation activates motor circuits in PD 10 rats; whereas, 5-HT1B receptor agonism reduces the overall locomotor activity of adult rats, perhaps by blunting exploratory tendencies.

Reciprocal cross-sensitization between cocaine and RU 24969 in male and female preweanling rats.

Neuronal adaptations involving dopaminergic, glutamatergic, and serotonergic neurotransmitter systems are responsible for behavioral sensitization. Because of common underlying mechanisms, cross-sensitization between compounds of different drug classes can be observed. The purpose of the present study was to determine whether a one- or four-day pretreatment regimen of RU 24969 (a 5-HT1A/1B receptor agonist) would reciprocally cross-sensitize with cocaine or methamphetamine in male and female preweanling rats. Rats were pretreated with RU 24969 (0 or 5 mg/kg) for 4 days (PD 17-20) and then challenged with cocaine (10 or 20 mg/kg) or methamphetamine (1 or 2 mg/kg) on PD 22. Reciprocal cross-sensitization was also assessed (i.e., rats were pretreated with psychostimulants and tested with RU 24969). In a follow-up experiment, the ability of RU 24969 and cocaine to reciprocally cross-sensitize was assessed using a one-day pretreatment regimen. Reciprocal cross-sensitization between cocaine and RU 24969 was evident in preweanling rats, whereas methamphetamine and RU 24969 did not cross-sensitize. When a one-trial pretreatment regimen was used, cross-sensitization was only detected when rats were pretreated with RU 24969 and tested with cocaine, but not the reverse. In sum, the present results show that the nonselective 5-HT1A/1B receptor agonist RU 24969 cross-sensitizes with cocaine, but not methamphetamine, in preweanling rats. This dichotomy may be a function of cocaine having a greater affinity for the serotonin transporter than methamphetamine.

Importance of dopaminergic neurotransmission for the RU 24969-induced locomotor activity of male and female rats during the preweanling period.

There is disagreement about whether the locomotor activity produced by serotonin (5-HT) 1A/1B receptor agonists is ultimately mediated through a dopaminergic mechanism or is independent of dopamine (DA) system functioning. Using a developing rat model, we examined whether DA neurotransmission is necessary for the locomotor activity produced by 5-HT1A/1B receptor stimulation. Depending on experiment, male and female preweanling rats were pretreated with vehicle, the monoamine-depleting agent reserpine, the 5-HT synthesis inhibitor 4-chloro-DL-phenylalanine methyl ester hydrochloride (PCPA), the DA synthesis inhibitor ∝-methyl-DL-p-tyrosine (AMPT), or the D1 and D2 receptor antagonists SCH 23390 and raclopride, respectively. After completing the pretreatment regimen, the behavioral effects of saline and the 5-HT1A/1B receptor agonist RU 24969 were assessed during a 2-h test session. Locomotor activity in the center and margin of the testing chamber was recorded. RU 24969's locomotor activating effects were sensitive to blockade of the D2 receptor, but not the D1 receptor. The DA synthesis inhibitor (AMPT) significantly attenuated the RU 24969-induced locomotor activity of preweanling rats, as did the 5-HT synthesis inhibitor PCPA. The latter result suggests that presynaptic 5-HT1A/1B receptors may have a role in mediating RU 24969-induced locomotion during the preweanling period. DA neurotransmission, especially involving D2 receptors, is necessary for the 5-HT1A/1B-mediated locomotor activity of preweanling rats. The actions of PCPA, reserpine, and SCH 23390 differ substantially between preweanling and adult rats, suggesting that the neural mechanisms underlying these DA/5-HT interactions vary across ontogeny.

Serotonin 5-HT1A and 5-HT1B receptors co-mediate the RU 24969-induced locomotor activity of male and female preweanling rats.

The serotonin (5-HT) 1A/1B agonist RU 24969 robustly increases the locomotor activity of adult male rats and mice; however, studies using selective antagonists alternately report that 5-HT1A, 5-HT1B, or both receptor types mediate RU 24969's locomotor activating effects. The purpose of the present study was to extend these past findings by administering a selective 5-HT1 agonist and/or antagonists to male and female preweanling rats. This age group was tested because younger rats often exhibit psychopharmacological responses that are quantitatively or qualitatively different from adult rats. In a series of experiments, male and female preweanling rats were pretreated with vehicle, the 5-HT1A antagonist WAY 100635 (0.5, 1, 5, or 10 mg/kg), or the 5-HT1B antagonists NAS-181 (5 or 10 mg/kg) or SB 216641 (5 or 10 mg/kg) 30 min before assessment of locomotor activity. Rats were injected with saline or RU 24969 immediately prior to testing. Results showed that RU 24969 (0.625, 1.25, 2.5, or 5 mg/kg) significantly increased the locomotor activity of both male and female preweanling rats (no sex differences were apparent). Antagonism of either the 5-HT1A or the 5-HT1B receptor was sufficient to significantly reduce the locomotor activity of RU 24969-treated preweanling rats. Unexpectedly, NAS-181 did not act as a silent receptor antagonist, as both doses of NAS-181 significantly increased the locomotor activity of saline-treated preweanling rats. In sum, the present results show that both the 5-HT1A and 5-HT1B receptor systems mediate locomotion during the late preweanling period, and this mediation does not vary according to sex.

Effects of dopamine and serotonin synthesis inhibitors on the ketamine-, d-amphetamine-, and cocaine-induced locomotor activity of preweanling and adolescent rats: sex differences.

The pattern of ketamine-induced locomotor activity varies substantially across ontogeny and according to sex. Although ketamine is classified as an NMDA channel blocker, it appears to stimulate the locomotor activity of both male and female rats via a monoaminergic mechanism. To more precisely determine the neural mechanisms underlying ketamine's actions, male and female preweanling and adolescent rats were pretreated with vehicle, the dopamine (DA) synthesis inhibitor ∝-methyl-DL-p-tyrosine (AMPT), or the serotonin (5-HT) synthesis inhibitor 4-chloro-DL-phenylalanine methyl ester hydrochloride (PCPA). After completion of the pretreatment regimen, the locomotor activating effects of saline, ketamine, d-amphetamine, and cocaine were assessed during a 2 h test session. In addition, the ability of AMPT and PCPA to reduce dorsal striatal DA and 5-HT content was measured in male and female preweanling, adolescent, and adult rats. Results showed that AMPT and PCPA reduced, but did not fully attenuate, the ketamine-induced locomotor activity of preweanling rats and female adolescent rats. Ketamine (20 and 40 mg/kg) caused a minimal amount of locomotor activity in male adolescent rats, and this effect was not significantly modified by AMPT or PCPA pretreatment. When compared to ketamine, d-amphetamine and cocaine produced different patterns of locomotor activity across ontogeny; moreover, AMPT and PCPA pretreatment affected psychostimulant- and ketamine-induced locomotion differently. When these results are considered together, it appears that both dopaminergic and serotonergic mechanisms mediate the ketamine-induced locomotor activity of preweanling and female adolescent rats. The dichotomous actions of ketamine relative to the psychostimulants in vehicle-, AMPT-, and PCPA-treated rats, suggests that ketamine modulates DA and 5-HT neurotransmission through an indirect mechanism.

Site-specific phosphorylation and caspase cleavage of GFAP are new markers of Alexander disease severity.

Alexander disease (AxD) is a fatal neurodegenerative disorder caused by mutations in glial fibrillary acidic protein (GFAP), which supports the structural integrity of astrocytes. Over 70 GFAP missense mutations cause AxD, but the mechanism linking different mutations to disease-relevant phenotypes remains unknown. We used AxD patient brain tissue and induced pluripotent stem cell (iPSC)-derived astrocytes to investigate the hypothesis that AxD-causing mutations perturb key post-translational modifications (PTMs) on GFAP. Our findings reveal selective phosphorylation of GFAP-Ser13 in patients who died young, independently of the mutation they carried. AxD iPSC-astrocytes accumulated pSer13-GFAP in cytoplasmic aggregates within deep nuclear invaginations, resembling the hallmark Rosenthal fibers observed in vivo. Ser13 phosphorylation facilitated GFAP aggregation and was associated with increased GFAP proteolysis by caspase-6. Furthermore, caspase-6 was selectively expressed in young AxD patients, and correlated with the presence of cleaved GFAP. We reveal a novel PTM signature linking different GFAP mutations in infantile AxD.