Olig2 is an important transcription factor essential for the specification and differentiation of oligodendrocytes as well as astrocytes and neurons during developmental stages. However, Olig2 distribution pattern and its relationship among different types of glial cells in the adult central nervous system (CNS) are not well characterized. Here, we systematically examined Olig2 expression pattern in combination with major markers of neurons and glial cells throughout the brain and spinal cord in the adult mice. As expected, Olig2 is universally expressed in oligodendrocytes and oligodendrocyte precursor cells (OPCs), but not in neurons or microglia. Interestingly, we discover a subpopulation of Olig2+ astrocytes that are highly enriched in some specific regions including the olfactory bulb, thalamus, midbrain, medulla, and spinal cord in the adult mice. Moreover, OPCs have high expression level of Olig2, whereas oligodendrocytes and astrocytes have similar level of Olig2 expression. Our results suggest that a distinct population of Olig2+ astrocytes are highly concentrated in discrete regions in the adult CNS. Investigating the functional significance of these Olig2+ astrocytes in both resting state and pathological state of the brain and spinal cord may broaden our understanding on astrocytic heterogeneity and functions.

BACKGROUNDMechanisms underlying persistent cardiopulmonary symptoms following SARS-CoV-2 infection (post-acute sequelae of COVID-19 “PASC” or “Long COVID”) remain unclear. The purpose of this study was to elucidate the pathophysiology of cardiopulmonary PASC using multimodality cardiovascular imaging including cardiopulmonary exercise testing (CPET), cardiac magnetic resonance imaging (CMR) and ambulatory rhythm monitoring.METHODSIn the Long-Term Impact of Infection with Novel Coronavirus (LIINC) Cohort, we performed CMR, CPET, and ambulatory rhythm monitoring among adults > 1 year after PCR-confirmed SARS-CoV-2 infection. We used logistic and linear regression to compare those with and without cardiopulmonary symptoms (dyspnea, chest pain, palpitations) adjusting for confounders.RESULTSOne hundred twenty individuals were studied, among whom 46 participants (unselected for symptom status) had at least one advanced test performed at median 17 months (IQR 15-18). Median age was 52 (IQR 42-61), 18 (39%) were female, and 6 (13%) were hospitalized for severe acute infection. On CMR (n=39), smaller RV volume and stroke volume and higher extracellular volume were present among those with symptoms, but no evidence of late-gadolinium enhancement or differences in T1 or T2 mapping were demonstrated. We did not find arrhythmias on ambulatory monitoring. In contrast, on CPET (n=39), 13/15 (87%) participants with reduced exercise capacity (<85% predicted) reported cardiopulmonary symptoms or fatigue (p=0.008). Adjusted peak VO2 was 2.7 ml/kg/min lower among those with cardiopulmonary symptoms (95%CI −6.9 to 1.5; p=0.20) or −11% predicted (95%CI −27 to 5, p=0.17). Including fatigue along with cardiopulmonary symptoms, the adjusted difference in peak VO2 was −5.9 ml/kg/min (−9.6 to −2.3; p=0.002) or −21% predicted (−35 to −7; p=0.006). Chronotropic incompetence was the primary abnormality among 9/15 with reduced peak VO2. Adjusted heart rate reserve <80% was associated with reduced exercise capacity (OR 15.6, 95%CI 1.30-187; p=0.03). Those with chronotropic incompetence had higher hsCRP, lower heart rate recovery, and lower heart rate variability suggestive of autonomic dysfunction.CONCLUSIONSReduced exercise capacity and reduced heart rate response to exercise, and hsCRP are associated with persistent cardiopulmonary symptoms more than 1 year following COVID-19. Chronic inflammation and autonomic dysfunction may underlie cardiopulmonary PASC.Clinical PerspectiveWhat is New?Impaired chronotropic response to exercise is associated with reduced exercise capacity and cardiopulmonary symptoms more than 1 year after SARS-CoV-2 infection.Findings on ambulatory rhythm monitoring point to perturbed autonomic function, while cardiac MRIfindings argue against myocardial dysfunction and myocarditis.Clinical ImplicationsCardiopulmonary testing to identify etiologies of persistent symptoms in post-acute sequalae of COVID-19 or “Long COVID” should be performed in a manner that allows for assessment of heart rate response to exercise.Therapeutic trials of antiviral, anti-inflammatory, and exercise strategies in PASC are urgently needed and should include assessment of symptoms and objective testing with cardiopulmonary exercise testing.

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BACKGROUND Mechanisms underlying persistent cardiopulmonary symptoms following SARS-CoV-2 infection (post-acute sequelae of COVID-19 “PASC” or “Long COVID”) remain unclear. This study sought to elucidate mechanisms of cardiopulmonary symptoms and reduced exercise capacity. METHODS We conducted cardiopulmonary exercise testing (CPET), cardiac magnetic resonance imaging (CMR) and ambulatory rhythm monitoring among adults &gt; 1 year after confirmed SARS-CoV-2 infection in a post-COVID cohort, compared those with or without symptoms, and correlated findings with previously measured biomarkers. RESULTS Sixty participants (median age 53, 42% female, 87% non-hospitalized) were studied at median 17.6 months following SARS-CoV-2 infection. On CPET, 18/37 (49%) with symptoms had reduced exercise capacity (&lt;85% predicted) compared to 3/19 (16%) without symptoms (p = 0.02). Adjusted peak VO2 was 5.2 ml/kg/min lower (95%CI 2.1-8.3; p = 0.001) or 16.9% lower percent predicted (95%CI 4.3-29.6; p = 0.02) among those with symptoms. Chronotropic incompetence was common. Inflammatory markers and antibody levels early in PASC were negatively correlated with peak VO2 more than 1 year later. Late-gadolinium enhancement on CMR and arrhythmias were absent. CONCLUSIONS Cardiopulmonary symptoms &gt;1 year following COVID-19 were associated with reduced exercise capacity, which was associated with elevated inflammatory markers early in PASC. Chronotropic incompetence may explain exercise intolerance among some with cardiopulmonary Long COVID.