Osteoclast-mediated bone loss observed in a COVID-19 mouse model

Abstract

The consequences of SARS-CoV-2 infection on the musculoskeletal system represents a dangerous knowledge gap. Aging patients are at added risk for SARS-CoV-2 infection; therefore, a greater understanding of the resulting musculoskeletal sequelae of SARS-CoV-2 infection may help guide clinical strategies. This study examined fundamental bone parameters among mice treated with escalating viral loads. Male C57BL/6J (WT, n=17) and B6.Cg-Tg(K18-ACE2)2Prlmn/J mice (K18-hACE2 transgenic mice, n=21) expressing human ACE2 (TG) were divided into eight groups (n=4-6/group) and subjected to intranasal dosing of 0, 1x10 3 , 1x10 4 , and 1x10 5 PFU (plaque forming units) of human SARS-CoV-2. Animal health was assessed daily by veterinary staff using established and validated scoring criteria (activity, posture, body condition scores and body weight). We report here that mock and WT infected mice were healthy and completed the study, surviving until 12-14 days post infection (dpi). In contrast, the TG mice infected with 1x10 5 PFU all experienced severe health declines that necessitated early euthanasia (6-7 dpi). For TG mice infected with 1x10 4 PFU, 2 mice were also euthanized after 7 dpi, while 3 mice showed signs of moderate disease at day 6 dpi, but recovered fully by day 11 dpi. Four of the 5 TG mice that were infected with 1x10 3 PFU remained healthy throughout the study. This suggests that our study mimics what is seen during human disease, where some patients develop severe disease resulting in death, while others have moderate to severe disease but recover, and others are asymptomatic. At necropsy, femurs were extracted and analyzed by μCT. No difference was found in μCT determined bone parameters among the WT groups. There was, however, a significant 24.4% decrease in trabecular bone volume fraction (p=0.0009), 19.0% decrease in trabecular number (p=0.004), 6.2% decrease in trabecular thickness (p=0.04), and a 9.8% increase in trabecular separation (p=0.04) among surviving TG mice receiving any viral load compared to non-infected controls. No differences in cortical bone parameters were detected. TRAP staining revealed surviving infected mice had a significant 64% increase in osteoclast number, a 27% increase in osteoclast surface, and a 38% increase in osteoclasts per bone surface. While more studies are needed to investigate the long-term consequences of SARS-CoV-2 infection on skeletal health, this study demonstrates a significant reduction in several bone parameters and corresponding robust increases in osteoclast number observed within 2 weeks post-infection in surviving asymptomatic and moderately affected mice.

SARS-CoV-2 infection induces inflammatory bone loss in golden Syrian hamsters

“…In contrast, musculoskeletal sequelae have been increasingly reported in COVID-19 patients including those who have recovered from the acute phase of the infection 10 , 28 . During the revision of this work, it was also reported elsewhere that SARS-CoV-2 infection can induce bone loss in a lethal human ACE2-transgenic mouse model 30 – 32 . Nevertheless, it would be important to investigate the long-term bone changes not only in severe COVID-19 cases but also in mild to moderate ones, because most patients recover from the severe inflammation after proper treatment.…”

Extensive progressive heterotopic ossification post-Covid-19 in a man

“…On the other hand, this current patient also has diffuse osteopenia. Many cytokines that are increased due to COVID-19, including IL-1β, IL-6, IL-17, CXCL10, and TNF-α are known to regulate osteoclastogenesis and/or bone resorption suggesting these factors may contribute to the SARS-CoV-2 stimulated bone loss as was suggested using a COVID-19 mouse model (K18-hACE2 transgenic mice) even without changes in body weights, activity scores, and posture scores [22] .…”

Neuropilin‐1‐Mediated SARS‐CoV‐2 Infection in Bone Marrow‐Derived Macrophages Inhibits Osteoclast Differentiation

“…In a recent study, K18‐hACE2 transgenic mice were used to understand SARS‐CoV‐2 infection in macrophages. [ 39 ] Because we have clearly demonstrated that NRP1, rather than ACE2, mediates SARS‐CoV‐2 infection in BMMs, the use of hACE2 transgenic or transduction mouse model may be misleading in understanding the correlation between SARS‐CoV‐2 infection in BMMs and osteoclast differentiation. Therefore, in the present study use SARS‐CoV‐2 beta strain (B.1.351) that had been reported to be capable of infecting unmodified Balb/c mice.…”