Plural molecular and cellular mechanisms of pore domain KCNQ2 encephalopathy

KCNQ2 variants in children with neurodevelopmental impairment are difficult to assess due to their heterogeneity and unclear pathogenic mechanisms. We describe a child with neonatal-onset epilepsy, developmental impairment of intermediate severity, and KCNQ2 G256W heterozygosity. Analyzing prior KCNQ2 channel cryoelectron microscopy models revealed G256 as keystone of an arch-shaped non-covalent bond network linking S5, the pore turret, and the ion path. Co-expression with G256W dominantly suppressed conduction by wild-type subunits in heterologous cells. Ezogabine partly reversed this suppression. G256W/+ mice have epilepsy leading to premature deaths. Hippocampal CA1 pyramidal cells from G256W/+ brain slices showed hyperexcitability. G256W/+ pyramidal cell KCNQ2 and KCNQ3 immunolabeling was significantly shifted from axon initial segments to neuronal somata. Despite normal mRNA levels, G256W/+ mouse KCNQ2 protein levels were reduced by about 50%. Our findings indicate that G256W pathogenicity results from multiplicative effects, including reductions in intrinsic conduction, subcellular targeting, and protein stability. These studies reveal pore "turret arch" bonding as a KCNQ structural novelty and introduce a valid animal model of KCNQ2 encephalopathy. Our results, spanning structure to behavior, may be broadly applicable because the majority of KCNQ2 encephalopathy patients share variants near the selectivity filter.

KCNQ2/3 Gain-of-Function Variants and Cell Excitability: Differential Effects in CA1 versus L2/3 Pyramidal Neurons

Gain-of-function (GOF) pathogenic variants in the potassium channels KCNQ2 and KCNQ3 lead to hyperexcitability disorders such as epilepsy and autism spectrum disorders. However, the underlying cellular mechanisms of how these variants impair forebrain function are unclear. Here, we show that the R201C variant in KCNQ2 has opposite effects on the excitability of two types of mouse pyramidal neurons of either sex, causing hyperexcitability in layer 2/3 (L2/3) pyramidal neurons and hypoexcitability in CA1 pyramidal neurons. Similarly, the homologous R231C variant in KCNQ3 leads to hyperexcitability in L2/3 pyramidal neurons and hypoexcitability in CA1 pyramidal neurons. However, the effects of KCNQ3 gain-of-function on excitability are specific to superficial CA1 pyramidal neurons. These findings reveal a new level of complexity in the function of KCNQ2 and KCNQ3 channels in the forebrain and provide a framework for understanding the effects of gain-of-function variants and potassium channels in the brain.SIGNIFICANCE STATEMENT KCNQ2/3 gain-of-function (GOF) variants lead to severe forms of neurodevelopmental disorders, but the mechanisms by which these channels affect neuronal activity are poorly understood. In this study, using a series of transgenic mice we demonstrate that the same KCNQ2/3 GOF variants can lead to either hyperexcitability or hypoexcitability in different types of pyramidal neurons [CA1 vs layer (L)2/3]. Additionally, we show that expression of the recurrent KCNQ2 GOF variant R201C in forebrain pyramidal neurons could lead to seizures and SUDEP. Our data suggest that the effects of KCNQ2/3 GOF variants depend on specific cell types and brain regions, possibly accounting for the diverse range of phenotypes observed in individuals with KCNQ2/3 GOF variants.

AB1148 POST COVID-19 RHEUMATIC AND MUSCULOSKELETAL DISEASES

Background

Recent data suggests that SARS-Cov-2 can alter self-tolerance and trigger autoimmune responses through cross-reactivity with host cells; therefore it can lead to late autoimmune and inflammatory manifestations. With regard to rheumatic and musculoskeletal diseases (RMDs), medical literature displays sporadic case reports describing a variety of conditions diagnosed after COVID-19, but it remains still unclear what are the most common problems in patients presenting to rheumatology clinic following COVID-19 disease.

Objectives

To describe the pattern of post-COVID-19 RMDs in a consecutive group of patients from rheumatology outpatient clinic.

Methods

We have performed an observational descriptive study of a group of adult patients who received a new diagnosis of RMD within a timeframe of 12 weeks after the confirmation of COVID-19. Data was collected based on clinical presentation, paraclinical pattern and radiological examinations.

Results

The study included 23 patients who were consulted in rheumatology outpatient clinic and had post COVID-19 new onset joint, periarticular, bone or inflammatory syndrome manifestations. The general characteristics of the study group were as follows: mean age 45.5±11.3 (range 21-63) years and female to male ratio of 1.8:1. The majority of subjects consulted for joint symptoms (91.4%), in other cases reason for consultation was persistent low grade fever and fatigue (4.3%) and skin rash with dyspnea (4.3%). The mean duration of symptoms was 9.8±10.5 (range 1-42) weeks, and the time of onset after COVID-19 diagnosis was 4.9±4.1 (range 0-12) weeks. Concerning COVID-19 severity, it was established that in 60.9% it was mild, 17.4 % - moderate and 21.7% - severe. After clinical and paraclinical examination, the following diseases were diagnosed: ReA, lupus like syndromes, avascular necrosis, new onset RA and new onset PsA. In 69.7% of patients were diagnosed with ReA, the clinical pattern being joint or periarticular involvement of the hand, knee and feet. In 13.0% cases patients had multisystemic involvement (myocarditis, pericarditis, skin rash, inflammatory arthritis and/or low grade fever) and positive ANA and or dsDNA Ab, these cases were diagnosed as lupus like syndromes and followed a severe form of COVID-19. In 8.7% of patients who presented with non-inflammatory hip pain, avascular necrosis was diagnosed, in both cases femoral head being the affected part. No be noted that patients with avascular necrosis had a severe form of COVID-19 disease and joint pain started later after COVID-19 diagnosis (10-12 weeks). In 4.3% of cases each, new onset RA and PsA were identified.

Conclusion

In the present study we have found that COVID-19 can be followed by a variety of RMDs. The most common symptom of patients presenting with RMD was joint pain. The most common disease was post-COVID ReA (69.7%). Avascular necrosis (8.7%) and lupus like syndromes (13.0%) were found in patients who experienced a severe form of COVID-19. More rarely, patients had new onset of rheumatoid arthritis (4.3%) or psoriatic arthritis (4.3%). Our findings suggest that during the COVID-19 recovery period patients might experience onset of RDMs; therefore, in the presence of joint symptoms or other manifestations suggesting an autoimmune disease, patients should be referred to a rheumatologist for careful clinical examination.

References

[1]Kocyigit, B. F., & Akyol, A. (2021). Reactive arthritis after COVID-19: a case-based review. Rheumatology international, 41(11), 2031–2039.

[2]Liu, Y., Sawalha, A. H., & Lu, Q. (2021). COVID-19 and autoimmune diseases. Current opinion in rheumatology, 33(2), 155–162.

Disclosure of Interests

None declared

AB1141 THE PATTERN OF POST COVID-19 REACTIVE ARTHRITIS

Background

According to the recent medical literature, COVID-19 disease can lead to a constellation of clinical syndromes lasting well beyond the first 30 days of infection. The most common post COVID sequalae includes pulmonary, nervous system and neurocognitive, mental, metabolic, cardiovascular, gastrointestinal and several other clinical manifestations. Regarding joint involvement and particularly reactive arthritis (ReA), literature data is limited and describes case reports or series of cases of patients diagnosed with this condition following COVID-19 disease.

Objectives

To describe the pattern and the management of post-COVID reactive arthritis.

Methods

We have conducted a descriptive study of consecutive adult patients who presented to rheumatology outpatient clinic for joint or peri-articular pain/swelling/stiffness and received a diagnosis of post-COVID 19 reactive arthritis, by excluding other types of rheumatological conditions. The assessed clinical variables were: visual analogue scale (VAS) pain, swollen joint count (SJC), tender joint count (TJC), duration of morning stiffness, presence of enthesitis/tendinitis and axial involvement. Biochemistry and serology was performed: rheumatoid factor, ACPA, ANA, HLA B27, antiChlamydia Trachomatis, Ureaplasma Urealyticum and Mycoplasma Hominis Ab, anti HBs and HBc Ab, and anti HCV. COVID-19 disease prior to diagnosis of ReA was confirmed by PCR test.

Results

In the study were included 16 patients with confirmed post COVID-19 ReA. The mean age of the study group was 43.5±10.8 (range 21-60), the female: male ratio was 4:1 and the duration of joint symptoms was 10.4±11.8 (range 1-42) weeks. The severity of COVID-19 disease was mild in 68.7% cases, moderate in 18.7% and severe in only 6.2% of the cases. The duration between COVID-19 diagnosis and ReA varied between cases, with a mean value of 4.3±4.2 (range 1-12) weeks. In 43.7% of the cases patients had peripheral joint involvement (synovitis), in 37.5% - periarticular involvement (enthesitis), 6.25% - isolate axial involvement (sacroiliac joints), 6.25% enthesitis and axial involvement (cervical spine) and 6.25% synovitis and enthesitis. In patients with peripheral joint pattern, the distribution of pain was symmetric (71.4%). The pattern of synovitis was determined by a TJC of 6.25±5.2 (range 1-16) joints and SJC 1.6±2.4 (range 0-7) joints. Both TJC and SJC correlated positively with the duration of morning stiffness (r=0.9 and r=0.6), but did not correlate with the VAS pain scale. In most of the cases synovitis affected the hand (wrist, MCP and PIP) 62.5% and the knee, feet and ankles – 50%. Two patients presented with monoarthritis, 1 with oligoarthritis and 5 with polyarthritis, in the majority of cases, involvement being symmetric (75%). Periarticular pattern was determined by enthesitis, affecting the elbow and shoulder (50%), costo-sternal enthesitis (25%) and trochanteritis (25%). From the entire study group, 31.2% had elevated serum inflammatory markers (ESR and/or CRP). Patients responded well to NSAIDs alone in 68.7% cases, local (intra-articular or peri-articular infiltrations) or and systemic corticoids (5 mg Prednisolone equivalent) were administered in 5.3% and 12.5% cases respectively, in 12.5% cases (two patients) Methotrexate was administered.

Conclusion

Reactive arthritis represents a post COVID-19 sequelae. The time of onset of ReA varied between 1 and 12 weeks after COVID-19 diagnosis. The clinical pattern of the disease was expressed by joint or periarticular involvement, mainly affecting the hand, feet and knee symmetrically. Cases of axial manifestations were less common. Most of the patients responded well to NSAIDs, only in a few particular cases, low doses of corticoids and/or Methotrexate were recommended.

References

[1]Kocyigit, B. F., & Akyol, A. (2021). Reactive arthritis after COVID-19: a case-based review. Rheumatology international, 41(11), 2031–2039.

[2]Xie, Y., Bowe, B., & Al-Aly, Z. (2021). Burdens of post-acute sequelae of COVID-19 by severity of acute infection, demographics and health status. Nature communications, 12(1), 6571.

Disclosure of Interests

None declared

Flexible Stoichiometry: Implications for KCNQ2- and KCNQ3-Associated Neurodevelopmental Disorders

KCNQ2 and KCNQ3 pathogenic channel variants have been associated with a spectrum of developmentally regulated diseases that vary in age of onset, severity, and whether it is transient (i.e., benign familial neonatal seizures) or long-lasting (i.e., developmental and epileptic encephalopathy). KCNQ2 and KCNQ3 channels have also emerged as a target for novel antiepileptic drugs as their activation could reduce epileptic activity. Consequently, a great effort has taken place over the last 2 decades to understand the mechanisms that control the assembly, gating, and modulation of KCNQ2 and KCNQ3 channels. The current view that KCNQ2 and KCNQ3 channels assemble as heteromeric channels (KCNQ2/3) forms the basis of our understanding of KCNQ2 and KCNQ3 channelopathies and drug design. Here, we review the evidence that supports the formation of KCNQ2/3 heteromers in neurons. We also highlight functional and transcriptomic studies that suggest channel composition might not be necessarily fixed in the nervous system, but rather is dynamic and flexible, allowing some neurons to express KCNQ2 and KCNQ3 homomers. We propose that to fully understand KCNQ2 and KCNQ3 channelopathies, we need to adopt a more flexible view of KCNQ2 and KCNQ3 channel stoichiometry, which might differ across development, brain regions, cell types, and disease states.

KCNQ3 is the principal target of retigabine in CA1 and subicular excitatory neurons

Retigabine is a first-in-class potassium channel opener approved for patients with epilepsy. Unfortunately, several side effects have limited its use in clinical practice, overshadowing its beneficial effects. Multiple studies have shown that retigabine acts by enhancing the activity of members of the voltage-gated KCNQ (Kv7) potassium channel family, particularly the neuronal KCNQ channels KCNQ2-KCNQ5. However, it is currently unknown whether retigabine's action in neurons is mediated by all KCNQ neuronal channels or by only a subset. This knowledge is necessary to elucidate retigabine's mechanism of action in the central nervous system and its adverse effects and to design more effective and selective retigabine analogs. In this study, we show that the action of retigabine in excitatory neurons strongly depends on the presence of KCNQ3 channels. Deletion of Kcnq3 severely limited the ability of retigabine to reduce neuronal excitability in mouse CA1 and subiculum excitatory neurons. In addition, we report that in the absence of KCNQ3 channels, retigabine can enhance CA1 pyramidal neuron activity, leading to a greater number of action potentials and reduced spike frequency adaptation; this finding further supports a key role of KCNQ3 channels in mediating the action of retigabine. Our work provides new insight into the action of retigabine in forebrain neurons, clarifying retigabine's action in the nervous system.NEW & NOTEWORTHY Retigabine has risen to prominence as a first-in-class potassium channel opener approved by the Food and Drug Administration, with potential for treating multiple neurological disorders. Here, we demonstrate that KCNQ3 channels are the primary target of retigabine in excitatory neurons, as deleting these channels greatly diminishes the effect of retigabine in pyramidal neurons. Our data provide the first indication that retigabine controls neuronal firing properties primarily through KCNQ3 channels.

Quantitation of platelet adhesion to Ti and DLC-coated Ti in vitro using (125)I-labeled platelets

Measurement of platelet adhesion in vitro is a good indicator of its reactivity to implant devices in vivo. Platelets were labeled with I-125 without affecting its normal morphology and function and the labeled platelets were suspended in platelet poor plasma and exposed to Ti and diamond like carbon-coated (DLC) Ti discs, under dynamic conditions, using a parallel plate flow chamber. The test materials were washed, dried, exposed to a phosphor screen and scanned to get the images. The number of platelets that adhered to Ti was found to be higher than those that adhered to DLC coated Ti sample, irrespective of the shear stress which was varied between 2 and 16 dynes/cm(2).