COVID-19-Induced New-Onset Diabetes: Trends and Technologies.

The coronavirus disease 2019 (COVID-19) global pandemic continues to spread worldwide with approximately 216 million confirmed cases and 4.49 million deaths to date. Intensive efforts are ongoing to combat this disease by suppressing viral transmission, understanding its pathogenesis, developing vaccination strategies, and identifying effective therapeutic targets. Individuals with preexisting diabetes also show higher incidence of COVID-19 illness and poorer prognosis upon infection. Likewise, an increased frequency of diabetes onset and diabetes complications has been reported in patients following COVID-19 diagnosis. COVID-19 may elevate the risk of hyperglycemia and other complications in patients with and without prior diabetes history. It is unclear whether the virus induces type 1 or type 2 diabetes or instead causes a novel atypical form of diabetes. Moreover, it remains unknown if recovering COVID-19 patients exhibit a higher risk of developing new-onset diabetes or its complications going forward. The aim of this review is to summarize what is currently known about the epidemiology and mechanisms of this bidirectional relationship between COVID-19 and diabetes. We highlight major challenges that hinder the study of COVID-19-induced new-onset of diabetes and propose a potential framework for overcoming these obstacles. We also review state-of-the-art wearables and microsampling technologies that can further study diabetes management and progression in new-onset diabetes cases. We conclude by outlining current research initiatives investigating the bidirectional relationship between COVID-19 and diabetes, some with emphasis on wearable technology.

Long genes linked to autism spectrum disorders harbor broad enhancer-like chromatin domains.

Genetic variants associated with autism spectrum disorders (ASDs) are enriched in genes encoding synaptic proteins and chromatin regulators. Although the role of synaptic proteins in ASDs is widely studied, the mechanism by which chromatin regulators contribute to ASD risk remains poorly understood. Upon profiling and analyzing the transcriptional and epigenomic features of genes expressed in the cortex, we uncovered a unique set of long genes that contain broad enhancer-like chromatin domains (BELDs) spanning across their entire gene bodies. Analyses of these BELD genes show that they are highly transcribed with frequent RNA polymerase II (Pol II) initiation and low Pol II pausing, and they exhibit frequent chromatin-chromatin interactions within their gene bodies. These BELD features are conserved from rodents to humans, are enriched in genes involved in synaptic function, and appear post-natally concomitant with synapse development. Importantly, we find that BELD genes are highly implicated in neurodevelopmental disorders, particularly ASDs, and that their expression is preferentially down-regulated in individuals with idiopathic autism. Finally, we find that the transcription of BELD genes is particularly sensitive to alternations in ASD-associated chromatin regulators. These findings suggest that the epigenomic regulation of BELD genes is important for post-natal cortical development and lend support to a model by which mutations in chromatin regulators causally contribute to ASDs by preferentially impairing BELD gene transcription.

Biotin tagging of MeCP2 in mice reveals contextual insights into the Rett syndrome transcriptome.

Mutations in MECP2 cause Rett syndrome (RTT), an X-linked neurological disorder characterized by regressive loss of neurodevelopmental milestones and acquired psychomotor deficits. However, the cellular heterogeneity of the brain impedes an understanding of how MECP2 mutations contribute to RTT. Here we developed a Cre-inducible method for cell-type-specific biotin tagging of MeCP2 in mice. Combining this approach with an allelic series of knock-in mice carrying frequent RTT-associated mutations (encoding T158M and R106W) enabled the selective profiling of RTT-associated nuclear transcriptomes in excitatory and inhibitory cortical neurons. We found that most gene-expression changes were largely specific to each RTT-associated mutation and cell type. Lowly expressed cell-type-enriched genes were preferentially disrupted by MeCP2 mutations, with upregulated and downregulated genes reflecting distinct functional categories. Subcellular RNA analysis in MeCP2-mutant neurons further revealed reductions in the nascent transcription of long genes and uncovered widespread post-transcriptional compensation at the cellular level. Finally, we overcame X-linked cellular mosaicism in female RTT models and identified distinct gene-expression changes between neighboring wild-type and mutant neurons, providing contextual insights into RTT etiology that support personalized therapeutic interventions.

Elevating expression of MeCP2 T158M rescues DNA binding and Rett syndrome-like phenotypes.

Mutations in the X-linked gene encoding methyl-CpG-binding protein 2 (MeCP2) cause Rett syndrome (RTT), a neurological disorder affecting cognitive development, respiration, and motor function. Genetic restoration of MeCP2 expression reverses RTT-like phenotypes in mice, highlighting the need to search for therapeutic approaches. Here, we have developed knockin mice recapitulating the most common RTT-associated missense mutation, MeCP2 T158M. We found that the T158M mutation impaired MECP2 binding to methylated DNA and destabilized MeCP2 protein in an age-dependent manner, leading to the development of RTT-like phenotypes in these mice. Genetic elevation of MeCP2 T158M expression ameliorated multiple RTT-like features, including motor dysfunction and breathing irregularities, in both male and female mice. These improvements were accompanied by increased binding of MeCP2 T158M to DNA. Further, we found that the ubiquitin/proteasome pathway was responsible for MeCP2 T158M degradation and that proteasome inhibition increased MeCP2 T158M levels. Together, these findings demonstrate that increasing MeCP2 T158M protein expression is sufficient to mitigate RTT-like phenotypes and support the targeting of MeCP2 T158M expression or stability as an alternative therapeutic approach.

Tagging methyl-CpG-binding domain proteins reveals different spatiotemporal expression and supports distinct functions.

AIM: DNA methylation is recognized by methyl-CpG-binding domain (MBD) proteins. Multiple MBDs are linked to neurodevelopmental disorders in humans and mice. However, the functions of MBD2 are poorly understood. We characterized Mbd2 knockout mice and determined spatiotemporal expression of MBDs and MBD2-NuRD (nucleosome remodeling deacetylase) interactions. EXPERIMENTAL PROCEDURES: We analyzed behavioral phenotypes, generated biotin-tagged MBD1 and MBD2 knockin mice, and performed biochemical studies of MBD2-NuRD. RESULTS: Most behavioral measures are minimally affected in Mbd2 knockout mice. In contrast to other MBDs, MBD2 shows distinct expression patterns. CONCLUSION: Unlike most MBDs, MBD2 is ubiquitously expressed in all tissues examined and appears dispensable for brain functions measured in this study. We provide novel genetic tools and reveal new directions to investigate MBD2 functions in vivo.

Loss of MeCP2 function is associated with distinct gene expression changes in the striatum.

Rett syndrome (RTT) is a neurodevelopmental disorder characterized by developmental regression beginning 6-18months after birth, followed by a lifetime of intellectual disability, stereotyped behaviors, and motor deficits. RTT is caused by mutations in the gene encoding MeCP2, a methyl-CpG binding protein believed to modulate gene transcription. Gene expression studies of individual brain regions have reported that Mecp2 loss-of-function leads to both activation and repression of its gene targets in mice. Conditional deletion of MeCP2 from different brain regions has revealed unique insights into the role of these structures in mediating particular RTT-like phenotypes. However, the function of MeCP2 in the striatum, a major brain region involved in motor control and executive cognitive functions, has yet to be studied. Here, we characterized the gene expression changes in the striatum of Mecp2 mutant mice. We found a number of differentially expressed genes in the striatum of both constitutive Mecp2-null mice and mice lacking MeCP2 only from forebrain GABAergic neurons. These changes only occurred when MeCP2 expression levels had reached mature levels and RTT-like symptoms were manifest, supporting a role for MeCP2 in maintaining proper brain function. Many of the gene expression changes identified in the striatum have not previously been shown to change in the hypothalamus or cerebellum. Bioinformatic analysis of differentially expressed genes in striatum as well as hypothalamus and cerebellum revealed that loss of MeCP2 does not affect the global landscape of gene expression. Additionally, we uncovered a number of differentially expressed genes in the liver of Mecp2-null mice suggesting an important role for MeCP2 in non-neuronal tissues. Collectively, our data suggest that the differential expression of genes following loss of MeCP2 occurs in a tissue- or cell-type specific manner and thus MeCP2 function should be understood in a cellular context.

Ataxin-2 intermediate-length polyglutamine expansions are associated with increased risk for ALS.

The causes of amyotrophic lateral sclerosis (ALS), a devastating human neurodegenerative disease, are poorly understood, although the protein TDP-43 has been suggested to have a critical role in disease pathogenesis. Here we show that ataxin 2 (ATXN2), a polyglutamine (polyQ) protein mutated in spinocerebellar ataxia type 2, is a potent modifier of TDP-43 toxicity in animal and cellular models. ATXN2 and TDP-43 associate in a complex that depends on RNA. In spinal cord neurons of ALS patients, ATXN2 is abnormally localized; likewise, TDP-43 shows mislocalization in spinocerebellar ataxia type 2. To assess the involvement of ATXN2 in ALS, we analysed the length of the polyQ repeat in the ATXN2 gene in 915 ALS patients. We found that intermediate-length polyQ expansions (27-33 glutamines) in ATXN2 were significantly associated with ALS. These data establish ATXN2 as a relatively common ALS susceptibility gene. Furthermore, these findings indicate that the TDP-43-ATXN2 interaction may be a promising target for therapeutic intervention in ALS and other TDP-43 proteinopathies.

Prion-like disorders: blurring the divide between transmissibility and infectivity.

Prions are proteins that access self-templating amyloid forms, which confer phenotypic changes that can spread from individual to individual within or between species. These infectious phenotypes can be beneficial, as with yeast prions, or deleterious, as with mammalian prions that transmit spongiform encephalopathies. However, the ability to form self-templating amyloid is not unique to prion proteins. Diverse polypeptides that tend to populate intrinsically unfolded states also form self-templating amyloid conformers that are associated with devastating neurodegenerative disorders. Moreover, two RNA-binding proteins, FUS and TDP-43, which form cytoplasmic aggregates in amyotrophic lateral sclerosis, harbor a 'prion domain' similar to those found in several yeast prion proteins. Can these proteins and the neurodegenerative diseases to which they are linked become 'infectious' too? Here, we highlight advances that define the transmissibility of amyloid forms connected with Alzheimer's disease, Parkinson's disease and Huntington's disease. Collectively, these findings suggest that amyloid conformers can spread from cell to cell within the brains of afflicted individuals, thereby spreading the specific neurodegenerative phenotypes distinctive to the protein being converted to amyloid. Importantly, this transmissibility mandates a re-evaluation of emerging neuronal graft and stem-cell therapies. In this Commentary, we suggest how these treatments might be optimized to overcome the transmissible conformers that confer neurodegeneration.

TDP-43 is intrinsically aggregation-prone, and amyotrophic lateral sclerosis-linked mutations accelerate aggregation and increase toxicity.

Non-amyloid, ubiquitinated cytoplasmic inclusions containing TDP-43 and its C-terminal fragments are pathological hallmarks of amyotrophic lateral sclerosis (ALS), a fatal motor neuron disorder, and frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U). Importantly, TDP-43 mutations are linked to sporadic and non-SOD1 familial ALS. However, TDP-43 is not the only protein in disease-associated inclusions, and whether TDP-43 misfolds or is merely sequestered by other aggregated components is unclear. Here, we report that, in the absence of other components, TDP-43 spontaneously forms aggregates bearing remarkable ultrastructural similarities to TDP-43 deposits in degenerating neurons of ALS and FTLD-U patients [corrected] . The C-terminal domain of TDP-43 is critical for spontaneous aggregation. Several ALS-linked TDP-43 mutations within this domain (Q331K, M337V, Q343R, N345K, R361S, and N390D) increase the number of TDP-43 aggregates and promote toxicity in vivo. Importantly, mutations that promote toxicity in vivo accelerate aggregation of pure TDP-43 in vitro. Thus, TDP-43 is intrinsically aggregation-prone, and its propensity for toxic misfolding trajectories is accentuated by specific ALS-linked mutations.

A yeast TDP-43 proteinopathy model: Exploring the molecular determinants of TDP-43 aggregation and cellular toxicity.

Protein misfolding is intimately associated with devastating human neurodegenerative diseases, including Alzheimer's, Huntington's, and Parkinson's. Although disparate in their pathophysiology, many of these disorders share a common theme, manifested in the accumulation of insoluble protein aggregates in the brain. Recently, the major disease protein found in the pathological inclusions of two of these diseases, amyotrophic lateral sclerosis (ALS) and frontal temporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U), was identified as the 43-kDa TAR-DNA-binding protein (TDP-43), providing a molecular link between them. TDP-43 is a ubiquitously expressed nuclear protein that undergoes a pathological conversion to an aggregated cytoplasmic localization in affected regions of the nervous system. Whether TDP-43 itself can convey toxicity and whether its abnormal aggregation is a cause or consequence of pathogenesis remain unknown. We report a yeast model to define mechanisms governing TDP-43 subcellular localization and aggregation. Remarkably, this simple model recapitulates several salient features of human TDP-43 proteinopathies, including conversion from nuclear localization to cytoplasmic aggregation. We establish a connection between this aggregation and toxicity. The pathological features of TDP-43 are distinct from those of yeast models of other protein-misfolding diseases, such as polyglutamine. This suggests that the yeast model reveals specific aspects of the underlying biology of the disease protein rather than general cellular stresses associated with accumulating misfolded proteins. This work provides a mechanistic framework for investigating the toxicity of TDP-43 aggregation relevant to human disease and establishes a manipulable, high-throughput model for discovering potential therapeutic strategies.

Mitochondrial dysfunction precedes neurodegeneration in mahogunin (Mgrn1) mutant mice.

Oxidative stress, ubiquitination defects and mitochondrial dysfunction are commonly associated with neurodegeneration. Mice lacking mahogunin ring finger-1 (MGRN1) or attractin (ATRN) develop age-dependent spongiform neurodegeneration through an unknown mechanism. It has been suggested that they act in a common pathway. As MGRN1 is an E3 ubiquitin ligase, proteomic analysis of Mgrn1 mutant and control brains was performed to explore the hypothesis that loss of MGRN1 causes neurodegeneration via accumulation of its substrates. Many mitochondrial proteins were reduced in Mgrn1 mutants. Subsequent assays confirmed significantly reduced mitochondrial complex IV expression and activity as well as increased oxidative stress in mutant brains. Mitochondrial dysfunction was obvious many months before onset of vacuolation, implicating this as a causative factor. Compatible with the hypothesis that ATRN and MGRN1 act in the same pathway, mitochondrial dysfunction and increased oxidative stress were also observed in the brains of Atrn mutants. Our results suggest that the study of Mgrn1 and Atrn mutant mice will provide insight into a causative molecular mechanism common to many neurodegenerative disorders.

Tubulointerstitial nephritis and uveitis syndrome.

BACKGROUND: Uveitis in association with tubulointerstitial nephritis is a distinct clinical entity known as tubulointerstitial nephritis and uveitis(TINU) syndrome. The onset of uveitis most commonly follows the onset of the interstitial nephritis, but may also occur before or concurrently. The uveitis is usually bilateral, nongranulomatous, limited to the anterior segment, and generally responds well to topical or oral (when indicated) anti-inflammatory treatment. Interestingly, recurrent or chronic uveitis is common, in contrast to the tubulointerstitial nephritis, which typically resolves completely. CASE REPORT: Approximately 5 months after a biopsy confirmed the diagnosis of tubulointerstitial nephritis, a 13-year-old boy was brought to our clinic with symptoms of a red, photophobic right eye of 3 days duration. Examination revealed nongranulomatous anterior-segment inflammation in the right eye greater than the left. The uveitis responded very well to topical steroid and cycloplegic treatment. Follow-up examinations have shown a gradual decrease in the inflammation, with no ocular complications. CONCLUSION: TINU syndrome is an under-recognized disorder and may account for some cases of uveitis otherwise characterized as 'idiopathic." Since the uveitis may be the presenting sign in up to 36% of cases of TINU syndrome, it is important for eye care practitioners to consider this disorder when searching for systemic associations with uveitis. Prompt detection through referral or testing will allow speedy diagnosis and appropriate treatment for both the uveitis and the tubulointerstitial nephritis.